Thailand: Country Survey of Infectious Diseases
Chusana Suankratay, Henry Wilde, and Stephen Berger
a written and oral certification examination. The recent
Asian economic crisis started in Thailand in 1997/1998.
The country abounds with huge office and shopping
complexes, condominium projects, and some 150 private
hospitals (in Bangkok alone) that are mostly underused.
This led to unemployment due to collapse of some
industry segments that had overextended themselves.
Many workers migrated back home to their villages. The
currency (the Baht) was devalued from US$1 representing 25 Baht in 1997 to 40 in 1999. The former
government had virtually depleted its large foreign currency reserves by futile attempts to defend the Baht. Efforts
to repair the damage are now underway and are slowly
gaining control. Fortunately, and unlike Indonesia, there
was virtually no social unrest, and the crime rate increased
only moderately. City streets in Bangkok are relatively
safe during the day and night, and vehicular accidents,
particularly on highways, probably represent the greatest health and security risks to a traveler.
Historical and Socioeconomic Comments
Thailand has been an independent kingdom for
almost 2,000 years. It was never colonized successfully
by a foreign power, although this was attempted by the
Khmer during the 11th and 12th centuries, the Burmese
in the 18th century, the French in the late 19th century,
and the Japanese during World War II.
The absolute monarchy was terminated at the wish
of King Prajadhipok (Rama VII) in 1932. Thailand has
an effective system of public health built on a pyramid
of district health stations and small hospitals and a network of large well-equipped provincial medical centers
and tertiary care teaching hospitals in Bangkok, Chieng
Mai, Songklah, and Khon Khean, where there are well
established medical colleges. With a present population
of nearly 70 million, it is a vigorous democracy with many
political parties that quarrel loudly among themselves.
The press is completely free.Universities in Thailand graduate 650 physicians, 300 dentists, and 180 veterinarians
and have approximately 45,000 registered nurses, now
mostly trained by university programs. The literacy rate
is 93% for males and 91% for females, and the population growth rate is now 1.1%, one of the lowest for a
developing country. Life expectancy for males is 66 years
and for females 72 years. The medical education system
follows the Anglo-American model based on bedside
teaching and seminars. However, young graduates are
required to serve 3 years in district and provincial hospitals before being able to enter private practice or
specialist training. Graduate medical education is also
structured after the North American model and ends with
Common Disease Patterns
Viral Diseases
Human immunodeficiency virus infection and disease.
Human immunodeficiency virus (HIV) appeared first in
Thailand in 1984 and was brought there by homosexual tourists from Europe and the Americas. It first spread
in the male gay community, later to heterosexuals and
drug addicts.1 The incidence of acquired immunodeficiency syndrome (AIDS) patients was 5,632 in 1997. As
of August 1998, 88,403 cases of AIDS were officially
reported. Ninety-one percent were in the age group of
15 to 49, with a male to female ratio of 4.2:1.0. The estimated HIV seropositive rate in Thailand was 500,000,
700,000, and 780,000 in 1992, 1994, and 1997, respectively. Surprisingly, annual HIV serosurveillance has
shown a decrease of HIV infection, symptomatic HIV,
and AIDS. This was particularly pronounced among
commercial sex workers, the pregnant, and young military conscripts since 1997. This was most likely due to
a vigorous educational campaign, starting in grade school,
and condom promotion. In 1993, approximately 4% of
new recruits for the Royal Thai Army were found to be
HIV positive.2 This number is now down to 2%.The most
common opportunistic infections seen are tuberculosis,
cryptococcosis, histoplasmosis, penicilliosis, Pneumocystis
carinii, and toxoplasmosis. Every major medical center in
the Kingdom has specialists who deal with HIV-infected
Chusana Suankratay, MD, PhD: Infectious Disease Unit,
Department of Medicine, King Chulalongkorn Memorial
Hospital, Bangkok, Thailand; Henry Wilde, MD, FACP: Queen
Saovabha Memorial Institute, Bangkok, Thailand; Stephen
Berger, MD, FACP: Department of Geographic Medicine, Tel
Aviv Medical Center, Tel Aviv, Israel.
The authors had no financial or other conflicts of interest to
disclose.
Reprint requests: Professor Henry Wilde, Queen Saovabha
Memorial Institute, Bangkok 10330, Thailand.
J Travel Med 2001; 8:192–203.
192
Suankratay et al., Thailand: Country Survey
patients. General hospitals perform routine antibody
screening and most have access to Western blot testing
and viral load determination from reference laboratories.
All modern drugs, including protease inhibitors, are
available but too expensive for general use. Travelers
with HIV infection are more susceptible to many infectious diseases and often have a poor response to vaccines.
They should be made aware of an increased risk when
visiting a tropical developing region.
Dengue fever and dengue hemorrhagic fever. The dengue
virus belongs to the genus Flavivirus and comprises four
serotypes. The principal mosquito vector is Aedes aegypti
which breeds mainly indoors, in clean water, and within
artificial containers (large water jars, etc.). The vector feeds
on man during daytime. Dengue fever (DF) is an acute
febrile illness, not unlike influenza, and is usually associated
with myalgia, and arthralgia, and often, with a rash. It is
a mild disease in small children and more severe in older
children and adults. Mild to moderate thrombocytopenia
is usually observed.3
Dengue hemorrhagic fever (DHF) is characterized
by acute fever, a hemorrhagic diathesis, and a tendency
to develop a potentially fatal shock syndrome from capillary leak. Several epidemiological and serological studies have shown association between DHF and a
secondary-type antibody response that occurs in patients
with previous dengue virus infections. Thus, this syndrome is uncommon in visitors to dengue endemic
regions from the West. Dengue and dengue hemorrhagic
fever are major health problems in Southeast Asia and
are among the ten leading causes of hospitalization and
deaths in native children. The incidence has been increasing since 1992 in every age group. The highest risk is
between the ages of 5 and 9 years (540/100,000 population).4 Cases were mostly reported between June
and August (the rainy season) from every part of the
country, but particularly from northeastern Thailand. Prevention is by avoidance of mosquito bites during the day.
Treatment is symptomatic for DF and requires careful
attention to fluid replacement in DHF.
Viral hepatitis. All forms of viral hepatitis (A-G) have
been reported from Thailand. Hepatitis A virus (HAV)
infection usually occurs during childhood and is often
asymptomatic. This pattern is now changing, and outbreaks of hepatitis A in adults are being reported with
increasing frequency, as food and water hygiene have
improved. There are 1.27 /100,000 symptomatic cases
reported annually.5 Nevertheless, tourists leaving the
five-star hotel environment, are well advised to obtain
one of the new hepatitis A vaccines, prior to travel.6
Hepatitis B virus (HBV) infection is common, and
the carrier rate in Thailand is 5.2%, 9%, and 5.6%, in children, adults, and pregnant women, respectively.7,8 By the
193
age of 20, 40–60% of the population show serological evidence of infection (HBV serological markers). Infected
newborns have a carrier and chronic hepatitis rate that
approaches 100%. It eventually leads to cirrhosis and
hepatocellular carcinoma in the majority of long-term
carriers. Infection later in life usually occurs from contamination by blood products or body fluids. It carries
a much lower risk of the chronic carrier state. The usual
traveler without lifestyle problems is at virtually no risk
of acquiring hepatitis B. Modern recombinant hepatitis
B vaccines are readily available throughout Thailand. As
a matter of fact, Thailand was one of the first developing countries to inaugurate routine newborn hepatitis B
vaccination in 1988.
Hepatitis C virus (HCV), a flavivirus, can be transmitted by blood products and body fluids. In Thailand,
the prevalence of positive HCV-antibody and HCVRNA among healthy volunteer blood donors, is similar
to that in western countries, approximately 0.8–4%.9
Most of the infected are asymptomatic, but fulminant
hepatitis C has been observed. Chronic persistent infection develops in more than half of the patients. It eventually progresses to cirrhosis and hepatocellular carcinoma.
Alpha-interferon and ribavirin are available in Thailand.
Like HBV, hepatitis C carries no increased risk for travelers who have a normal lifestyle.
Hepatitis D virus (HDV), a defective RNA virus,
replicates only in the presence of HBV. A recent study
revealed a prevalence of HDV infection in Thailand of
65.48%, 11.1%, 8.3%, and 0% in intravenous drug users,
chronic active hepatitis patients, cirrhotic patients, and
asymptomatic HBV carriers, respectively.10
Hepatitis E virus (HEV) is an RNA calicivirus. The
infection is mostly transmitted by the fecal-oral route.
Outbreaks have been reported in South Asia. A recent
study showed that the prevalence of HEV infection
increased with age, from 1.8–6.2% in children and adolescents to 22% in adults.11 Clinical manifestations are similar to HAV, but in the pregnant there is a significantly
higher morbidity and mortality rate (15–20%). No vaccine is available. Preventive measures are the same as for
hepatitis A.
The hepatitis G virus (HGV) is a flavivirus. The significance of this virus as a cause of acute or chronic liver
disease remains unknown, but most studies have revealed
a benign course,either alone or as a co-infection with other
hepatotropic viruses such as HBV and HCV. The prevalence of HGV infection among various groups in Thailand has been investigated by the reverse transcriptase
polymerase chain reaction (PCR) method. It was found
to be 1-5%,18.2%,10%,and 1–5%,in healthy persons,intravenous drug users, prostitutes, and patients with chronic
liver disease,respectively.12 Routine diagnostic tests for HGV
infection are not available in most hospitals in Thailand.
Transmission is similar to that of hepatitis B and C.
194
The Japanese B encephalitis
(JE) virus is a flavivirus. It also is an arbovirus and the
infection is transmitted by a mosquito vector. The virus
multiplies in a reservoir host, mostly the pig. Other
vertebrates including cows, horses, and some birds may
also be infected. The mosquito vector, Culex
tritaeniorhyncus, breeds in close proximity to pig farms
and rice fields. The incidence of JE infection has
decreased, but morbidity and mortality rates have been
increasing, especially in children.13 JE has been reported
from the whole country, and every city in Thailand,
except Bangkok, where it is uncommon.14,15 The risk
of acquiring infection is relatively low for most travelers.
However, there have been cases among tourists during
the past 25 years, particularly among those who visited
r ural areas. Immunization with JE vaccine is
recommended for all nonimmune travelers to endemic
areas who plan to remain there for more than 2 weeks.
Travel plans and lifestyle should be considered on an
individual basis. Currently available vaccines are mouse
brain derived, inactivated products. The present
immunization schedule consists of 3 injections on day
0, 7, 14, or 28, with the second dose ideally given at least
1 month before entering an endemic area. Adverse side
effects are rare but do occur. They consist of local and
systemic reactions such as injection site tenderness, mild
fever, and headache. They should not prevent vaccination
where it is indicated. Measures to prevent mosquito
bites will reduce the risk of infection.
Japanese B encephalitis.
Rabies. Rabies has been endemic among Thailand’s
large stray and domestic canine populations, now
estimated at 10 million.16 Cases in other mammals and
wildlife have been reported (cattle, monkeys, gibbons,
bears, civets, bats, and large rats, etc.), but are considered
to have been incidental overflow infections from the
canine and feline reservoir. These should pose no usual
risk to travelers. However, any mammal bite should be
evaluated promptly. Between 300 and 400 human cases
used to be reported to the Thai Ministry of Public
Health (MPH) during the 1970s, and this number has
now decreased to less than 60 in 2000. The number of
rabid animals identified were 41,444 during 1985–1990
(95.4% dogs and 3.7% cats); 3,781 in 1994 (94.2% dogs);
1,857 in 1996 (95.3% dogs and 3.6% cats); and 1,111
in 1997.17 There are approximately 10 million dogs in
the country, of which fewer than 12% were vaccinated
as of 1990. Coverage increased to 53% in 1995, but this
is not enough to interrupt transmission. The reduction
in the number of human cases is largely due to an
intensive public education campaign, and the availability
of modern postexposure treatment. Human diploid cell
rabies vaccine is available, but inordinately expensive and
neither more effective nor reaction free than newer
J o u r n a l o f Tr a v e l M e d i c i n e , Vo l u m e 8 , N u m b e r 4
“second generation” tissue culture vaccines.These include
the Vero cell and purified chick and duck embryo
vaccines, which are less expensive and widely available
in Thailand. Human and equine rabies immune globulins
(HRIG and ERIG) are manufactured by the Thai Red
Cross in limited quantities for local use only. European
manufacturers of ERIG have now all discontinued
production of ERIG, and immune globulins are, thus,
in very short supply or not available at all in this region.
Nerve tissue derived vaccines (Semple and suckling
mouse products) have been discontinued in Thailand
since 1985. Rabies pre-exposure vaccination is
recommended for long-term residents, particularly
children, and for travelers who plan to venture off the
five-star hotel trail and expose themselves to the large
stray dog population. It is strongly recommended for
travelers who plan extensive touring to neighboring
countries including India, Cambodia, Laos, Burma, and
Vietnam, where tissue culture rabies vaccines and,
particularly, rabies immune globulins may not be available.
Travelers with HIV infection should know that they
might have a poor antibody response to pre- or
postexposure rabies vaccination and take extra
precautions not to come in contact with local mammals.
Bacterial Diseases
Tuberculosis. The incidence of clinical tuberculosis in
Thailand has been increasing since 1987 (from
33.6/100,000 in 1987, to 37.4/100,000 in 1995).18 This
is probably due to the high incidence of HIV infection.
However,the prevalence of TB infection (positive skin test)
has been decreasing (49% of the total population in 1962,
to 30% in 1991). This is probably due to universal BCG
vaccination of infants and improvement in living standards
and hygiene. The standard short course therapy using
four drugs (INH, rifampicin, pyrazinamide, and ethambutol) is widely used for pulmonary and extrapulmonary
tuberculosis.There is,however,an increasing treatment failure rate,partly due to an increasing rate of multidrug resistant TB (primary and secondary resistance to both INH
and rifampicin), which rose from 1.9% in 1991 to 8.8%
in 1996.19 Economic and logistic problems have prevented authorities from embarking on a case finding and
eradication program.
Nontuberculous
mycobacterium infection (NTM) was relatively rare in
Thailand in the pre-AIDS era. A study by the Central
Chest Hospital, Nonthaburi, from 1969 to 1978,
revealed pulmonary infection caused by NTM in only
24 cases, compared with 42 cases from 1979 to 1987.20,21
The organisms included Mycobacterium avium complex
(MAC) (50%), Mycobacterium scrofulaceum (16.6%),
Mycobacterium kansasii (14%), Mycobacterium gordonae
Nontuberculous mycobacterium.
Suankratay et al., Thailand: Country Survey
(9.5%), Mycobacterium simiae (1 case), Mycobacterium asiaticum (1 case), Mycobacterium szulgai (1 case), and
Mycobacterium fortuitum (1 case). Two other large reports
about NTM were from Siriraj Hospital and Khon
Kaen University.22,23 At present, due to the rising incidence of HIV infection, cases of NTM, particularly
MAC and M. kansasii, are quite common.24
Cholera. The incidence of cholera has decreased dur-
ing the past decades. Only rare cases and small clusters
have been reported and originate mostly in slums and
river estuaries. This is due to improvement of food and
water hygiene throughout the country. Both 01 and
non-01 cases are reported. Severe classic cholera is usually caused by 01 but can also be observed in non-01,
particularly in 0139 strains. Routine cholera vaccination
is not recommended for Thailand.
Enteric fever. Enteric fever is due to infection with Salmonella typhi or Salmonella paratyphi and is transmitted
via the fecal-oral route. The incidence has been slowly
decreasing in the past 10 years from 32/100,000 in
1984, to 28/100,000 population in 1993.25 However,
there were small outbreaks in 1986 (50/100,000), and
1990 (40/100,000). A seasonal variation has been
observed, with the peak incidence in summer, and
during the rainy seasons (between March and October). Enteric fever has been reported in every city of
the country, with the highest incidence in northern and
southern Thailand. Most patients live outside metropolitan areas (80–90%). However, there was an outbreak
of paratyphoid A in Bangkok in 1996.26 The high-risk
age group is between 10 and 14 years, and with equal
incidence in males and females. Oral and parenteral
typhoid vaccines are widely available in Thailand. The
older, crude, inactivated vaccine is rarely used now
due to a high rate of local and systemic side effects. The
Vi polysaccharide vaccine has a protection rate of
60–70% that lasts for fewer than 2 years. The oral
attenuated typhoid vaccine, containing a nonpathogenic
mutant of Salmonella typhi, Ty21a, has a protection
rate of approximately 70% for at least 3 years. Both current parenteral and oral typhoid vaccines offer no protection against parathyphoid fever, which is more
prevalent in Southeast Asia at this time. Sepsis and
solid organ abscess formation due to nontyphoidal
salmonellae are not uncommon. Abscesses localize
most often in spleen and liver and may cause aortitis,
particularly in the elderly.
Melioidosis. Burkholderia pseudomallei, a gram-negative
bacillus, is present in the soil of most of Southeast Asia. It
is an “iceberg disease” since only a small fraction of the
infected individuals will develop clinical signs and symp-
195
toms. A recent study among children in the northeastern
rural part of Thailand revealed that 12% of the 1–6-montholds had serological evidence of B. pseudomallei infection.
Numbers rose to 80% after the age of 40. Melioidosis is
most common in the northeastern part of the country but
has been reported from other parts, including Bangkok.27
Patients with diabetes,chronic renal failure,renal stone,thalassemia,alcoholism,but surprisingly not those with AIDS,
are known to be particularly susceptible to melioidosis.The
organism can manifest itself clinically in a wide variety of
syndromes ranging from rapidly progressive and fatal septicemia,acute as well as chronic granulomatous pneumonia,
localized abscess, meningitis, pericarditis, osteomyelitis,
and prolonged fever of undetermined origin.It is included
in the differential diagnosis of any case of obscure fever at
Thailand’s medical centers. Melioidosis has been seen in
both short and long term visitors,and expatriate residents.
It can remain a hidden asymptomatic infection for years
and decades, only to reactivate later as an acute or chronic
illness. This has been reported in Vietnam veterans. Early
diagnosis is crucial, and made by being aware of this disease, and knowing the travel history of the patient. The
organism can be easily isolated by conventional culture
methods.The isolation rates of B.pseudomallei in 1995 was
in 4.1/1,000 clinical specimens in northeastern hospitals,
as compared with 1.8,1.1,and 0.7/1,000 in central,northern,and southern hospitals,respectively.28 The current optimal treatment consists of ceftazidime with co-trimoxazole
during the acute phase,followed by amoxiclav (amoxicilin
plus clavulanic acid) during a maintenance period for
4–9 months.29 Imipenem or sulperazone (cefoperazone plus
sulbactam) have also been shown to be effective.
The incidence of travelers’ diarrhea has been decreasing in Thailand over the past two
decades. Yet, a recent study among expatriate soldiers participating in a rural military exercise showed that approximately 20% experienced diarrhea at some time during
their stay, that loose stools persisted for 6–24 hours, and
50% had nausea and vomiting and/or fever associated
with diarrhea. Only 13% of the affected had bloody or
mucous stools. Campylobacter spp and Escherichia coli
were the most common organisms identified, and there
were no cases of giardiasis or amoebiasis among this
group. Resistance to antibiotics of common bacilli causing travelers’ diarrhea in Thailand has been increasing. 3 0 Ninety percent of shigella and 40% of
enterotoxigenic E. coli (ETEC) are now resistant to
trimethoprim. One percent of ETEC and 84% of Campylobacter spp are resistant to ciprofloxacin, and 7–15% of
Campylobacter spp are also resistant to azithromycin.
Treatment of mild and moderate traveler’ diarrhea is now
best done by oral rehydration solution (ORS). Severe
cases with bloody diarrhea and fever should be evaluTravelers’ diarrhea.
196
ated by a local physician. Poorly cooked seafood and
chicken were thought to have been the most common
offending agents.
Leptospirosis. Several serotypes of Leptospira interrogans
complex have been reported from Thailand. These
include Leptospira bataviae, Leptospira javanica, Leptospira australis, Leptospira autumnalis, Leptospira icterohaemorrhagiae,
Leptospira pyrogenes, Leptospira pomona, Leptospira canicola,
Leptospira grippotyphosa, Leptospira hebdomadis, Leptospira
wolffi and Leptospira hyos.31 Human infections are more
common during the rainy season and from areas known
to flood. Many cases present as acute febrile illnesses and
may not be diagnosed unless they develop a fullblown
Weil’s syndrome. Treatment with penicillin has been
shown to be effective in shortening the course. The
Thai MPH reported 2,349 cases in 1997. Travelers do
not appear to be at significant risk.
Hansens disease. Hansens disease used to be a signifi-
cant public health problem in Thailand, and there are still
leprosaria near Bangkok, Chieng Mai, and southern
Thailand. Vigorous efforts by the MPH over the past
decades have made this a relatively rare disease. Only 586
cases were reported in 1997. However, old cases are still
seen, often as beggars on Bangkok’s streets.
Sexually transmitted diseases. The true incidence of
sexually transmitted diseases (STDs) is not known,
since they are not reportable, and self-medication with
antibiotics is relatively common in Thailand. However,
a rising incidence of Neisseria gonorrhoea, Mycoplasma
hominis, Chlamydia trachomatis, Ureaplasma urealyticum,
and Haemophilus ducreyi infection was observed during
1967 to 1987, in the pre-AIDS era.32,33 The annual incidence of syphilis lymphogranuloma venereum (LGV)
and granuloma inguinale (GI) are relatively stable, in
the range of 0.2–0.4/1,000 cases. Since 1984, when the
first case of AIDS was reported, the incidence of STDs
has slowly decreased. This is most likely due to a vigorous educational campaign, starting in grade school,
and condom promotion. There is now high-level resistance to tetracycline and fluoroquinolones. At the present, however, a single dose of ciprofloxacin 500 mg,
ofloxacin 400 mg, cefixime 400 mg, or ceftriaxone 125
mg is still effective in uncomplicated gonococcal urethritis. A single 1-g dose of azithromycin was found to
be more effective than the tetracyclines in nongonococcal urethritis.
Plague is an acute febrile zoonotic disease
caused by Yersinia pestis. The life cycle involves susceptible rodents and efficient flea vectors. Humans and other
nonrodent mammals are incidental hosts. The first case
Plague.
J o u r n a l o f Tr a v e l M e d i c i n e , Vo l u m e 8 , N u m b e r 4
in Thailand was reported in 1904,and plague subsequently
spread to major port cities through the country. Since
then, the spread of plague has been halted due to extensive surveillance, education, and environmental management. The last case was reported in 1952.34
Anthrax. Anthrax is an acute bacterial infection caused
by Bacillus anthracis. The most common clinical manifestation is cutaneous anthrax, which is characterized by
the development of a localized skin lesion with a central eschar surrounded by marked nonpitting edema.
Inhalation anthrax involves hemorrhagic mediastinitis,
rapidly progressive systemic infection, and a very high
mortality rate. Gastrointestinal anthrax, which is caused
by ingestion of inadequately cooked meat from animals
with anthrax, is also observed. In Thailand, the incidence has been decreasing since 1972. At present, the
annual incidence is approximately 0.15/100,000 population.35 Anthrax is most common in the northeastern
and northern parts of the country, but it has been reported
from other parts. The disease is an unlikely hazard for travelers who should not eat uncooked or poorly cooked
meat.
Rickettsial diseases. Rickettsial diseases are classified
into five general groups: (1) tick- and mite-borne spotted fever group (SFG) rickettsial diseases; (2) flea- and
louse-borne typhus group rickettsia; (3) chigger-borne
scrub typhus; (4) ehrlichioses; and (5) Q fever. In Thailand, all groups are present except ehrlichioses. One case
of Q fever was reported in Samutsakorn.36 Thai tick
typhus, an SFG rickettsial disease, was reported in northern Thailand.37 The species of rickettsia that causes the
disease is unknown. The patients presented with fever,
headache, lymphadenopathy, and petechial maculopapular
rash. Murine typhus is commonly reported in southern
Thailand.38 The disease is caused by Rickettsia typhi, with
rats as the reservoir and fleas as the vector. Most patients
live in metropolitan areas due to the natural habitat of
the vector. It manifests as acute febrile illness, with associated headache, myalgia, arthralgia, lymphadenopathy,
and nonpetechial maculopapular rash. Lastly, scrub typhus,
the most common group, was reported throughout the
country including Bangkok. The causative organism is
Orientia tsutsugamushi. In contrast to murine typhus,
most patients live outside metropolitan areas. Orientia tsutsugamushi is maintained in nature by transovarian transmission in trombiculid mites, mainly the genus
Leptotrombidium.39 The illness varies in severity from
mild and self-limiting to fatal. Usually, it is characterized
by acute fever, headache, myalgia, lymphadenopathy.
The classic case description includes an eschar at the site
of chigger feeding, which is more common in the groin
or axilla. Fewer than 30% of patients develop eschars.
Suankratay et al., Thailand: Country Survey
Severe cases include encephalitis, meningitis, myocarditis, and pneumonitis. Travelers do not appear to be at significant risk, even though a few cases were reported.
Parasitic Diseases
Protozoa. Malaria. All four forms of malaria have been
reported from Thailand. Falciparum malaria was the
most common form in 1994 (58%) and vivax came
second (41%), except in the southern part of the country
where vivax is more common than falciparum malaria.40
Ovale and malariae malaria make up the small remainder.
In the past two decades, malaria endemic regions have
been shrinking, now involving mostly land near the
borders with Myanmar and Cambodia. There are small
pockets on a few islands and along the Malaysian border
(Fig. ). This is due to the ample presence of the main
vectors (Anopheles dirus, Anopheles minimus, and Anopheles
maculatus, and others) in these regions. Even though the
overall malarious areas have become smaller, control of
the disease in these regions has not improved due to
socioeconomic and political reasons, warfare, and
migration of refugees across borders.
The central part of Thailand and the cities, usually
visited by tourists, have been free of malaria for over one
decade, with the exception of Kanchanaburi Province and
the River Kwai region (Fig.). The northern part contributes 44% of all malaria in Thailand, with Tak and Mae
Hongsorn heading the list. Northeastern Thailand contributes only 7% of malaria cases, with most coming from
Ubon Ratchathani and Srisaket. Southern Thailand has
an increasing incidence of malaria, in contrast to the rest
of the country, where it is decreasing. This is partly due
to migration of workers from nonimmune regions into
coffee-growing parts of the south (rural Yala, Ranong,
Ratchaburi, and Prachuab Kirikan Provinces).
Vivax malaria is still sensitive to chloroquine and primaquine. However, rare cases resistant to both of these
drugs are now emerging. Falciparum malaria is virtually
always resistant to chloroquine, the combination of sulfadoxine and pyrimethamine (Fansidar),and all of the other
old drugs except quinine. However, resistance to quinine
has now also been reported.The artesunate group of drugs,
when used with mefloquine, are nearly 100% effective in
nonsevere falciparum malaria.41,42 Purified and standardized oral and intravenous preparations of artesunate are
available in Thailand and now widely used.43
Malarone, a combination drug containing atovaquone (mepron) and proguanil, has recently been USFDA approved for the treatment and prevention of
multidrug-resistant falciparum malaria. It has to be taken
daily and is not available in Thailand.
The Thai Ministry of Health currently recommends
no chemoprophylaxis, since the risk of infection is low
197
and all of the presently available regimens are unreliable.
No drug for “true causal prophylaxis” is currently available. None have activity against sporozoites (the stage of
the parasite that is injected by the mosquito). Mefloquine,
halofantrine, and doxycycline, the currently prescribed
drugs for chemoprophylaxis, are at best only “suppressive.” They just kill schizonts and, after stopping the
medication, some nonimmune travelers may still develop
clinical malaria and late relapses. Standby treatment is an
alternative approach, but we have insufficient data regarding the available drugs to make recommendations with
confidence.44
Primary prevention consists of avoidance of mosquito bites by using netting, repellents, and not being in
malarious areas whenever possible, particularly after dusk.
Malaria is particularly dangerous, and can be rapidly
fatal, in the pregnant and in nonimmune children.
Leishmaniasis. Leishmaniasis is transmitted by the bite of
female phlebotomine sandflies (genus Phlebotomus [Old
World] or Lutzomyia [New World]). Visceral leishmaniasis (kala azar) is typically, but not exclusively, caused
by obligate intracellular flagellated protozoa, Leishmania
donovani. Thailand is not an endemic area, since the
sandfly vector is not present. However, the first 2 cases,
a person from Pakistan, and a child from Bangladesh, were
reported in 1960 and 1983. Since then, 6 Thai cases, in
people who came back from the Middle East, have
been reported.45
Amoebiasis. All forms of amoebiasis used to be common
in Thailand, but the incidence of intestinal and extraintestinal infestation have decreased dramatically over the
past two decades. The MPH reported only 1,525 cases
of amoebic dysentery, compared with 3,007 cases of
bacillary dysentery in 1995.Most cases of liver abscess seen
at Bangkok tertiary care hospitals are now pyogenic in origin,or are found in travelers or immigrants from the Indian
subcontinent. Usual treatment in intestinal amoebiasis is
metronidazole 750 mg tid for 10 days. If one decides to
treat asymptomatic cyst carriage, either paromomycin or
diiodohydroxyquinoline can be used.
Giardiasis. Infestation with Giardia lamblia is still seen and
is more common in rural regions, and among immigrants
or illegal workers from neighboring countries, or in
refugee camps. It is an uncommon infestation among
tourists. The standard treatment is metronidazole 250 mg
tid for 5 days.
Nematodes. Anisakiasis. Anisakiasis is caused by ingestion
of Anisakis simplex larvae present in infected raw seafood,
particularly in fish. The first case in Thailand was reported
in 1987.46 The patient from Phangnga Province presented
198
J o u r n a l o f Tr a v e l M e d i c i n e , Vo l u m e 8 , N u m b e r 4
•
Chiang Mai
Figure. Malaria transmission in Thailand. Note
that areas with serious risk of transmission are
mostly located at Myanmar, Lao, and Cambodian
borders.
ACTIVE TRANSMISSION REPORTED
(High risk areas after dusk)
VECTORS PRESENT BUT NO TRANSMISSION
(low risk but avoid mosquito bites)
VECTORS SUSPECTED TO BE STILL PRESENT
(virtually no risk)
NO VECTORS, NO TRANSMISSION
(malaria free areas)
Capillariasis. Most cases in Thailand are caused by Capillaria philippinensis. Chronic diarrhea with associated
malabsorption is the most common manifestation, and
this disease has led to fatalities when not recognized. Treatment consists of electrolyte replacement, administration
of an antidiarrheal agent, and mebendazole, or albendazole, or ivermectin. The first case was reported in 1973,47
and since then small outbreaks have been observed in central and northeast Thailand.48
becued pork sausages are the usual cause of infestation.
At least 3,000 cases have been reported in Thailand
since 1962 (annual rate is approximately 0.5/100,000).
There were 78 reported cases in 1997. An outbreak
involving more than a dozen cases, some in expatriate
residents, occurred in the north due to an embassy garden party that served poorly cooked sausages. Mild infections respond to analgesics and antipyretics. More severe
cases can be treated effectively with corticosteroids and
albendazole. A small cluster-outbreak of infestations (59
cases) by Trichinella pseudospiralis occurred in Chumporn
province in southern Thailand during 1994–1995.49
This rare form of trichinosis is characterized by a more
prolonged clinical course, as the parasite life span in
humans is longer, and encystment is delayed.
Trichinosis. Trichinosis (Trichinella spiralis) is not uncommon in northern Thailand, and poorly cooked or bar-
Gnathostomiasis. Gnathostoma spinigerum can cause one
form of larva migrans (dog hookworm is another)
with lower gut obstruction, and underwent laparotomy,
and was found to have a palpable mass in the ileum. No
specific drug for this nematode is available. This parasite
should present no significant risk to the traveler who is
unlikely to indulge much in raw fish.
Suankratay et al., Thailand: Country Survey
that is not uncommon among natives who may eat
improperly cooked fish, frogs, birds, and snakes. Humans
are an accidental host, and this rather large worm
(10–50 mm) can lodge in the central nervous system,
causing hemorrhage, and focal neurological signs.
Treatment is not very satisfactory, although both albendazole and praziquantel are usually used. Of stray dogs
in Bangkok, 2.8% were infested in 1980. G. spinigerum,
Gnathostoma vietnamicum, and Gnathostoma hispidum
are commonly present in swamp eels (Fluta alba), with
highest rates during October to December. Of these
eels, 10% are infested in Lop Buri province and 68.7%
in Nakhon Nayok province.50 The authors have not
seen any cases of neurognathostomiasis in visitors but
have seen several cases of peripheral larva migrans presumably due to this worm (diagnosis based on clinical picture and positive serology).
Angiostrongyliasis. Three species of angiostrongylus are
present in Thailand: Angiostrongylus cantonensis,
Angiostrongylus malaysiensis, and Angiostrongylus siamensis.51,52 A. cantonensis, the most common reported species,
is a filiform roundworm 15–30 mm in length that has
a complicated life cycle involving rodents and mollusks. Humans are accidental hosts who are infected by
eating raw or poorly cooked snails, crabs, prawns, or contaminated vegetables. When infecting humans, the worm
has a predilection for the central nervous system, where
it causes the syndrome of eosinophilic meningitis.
Angiostrongyliasis has been reported in Thailand since
the 1960s, and the highest prevalence is observed in the
north. The annual rate is approximately 2/100,000. A
survey of angiostrongylus infection in rats and snails in
the provinces of the northeast revealed an infection rate
among these animals in the range of 0.9–3.8%. Cases in
visitors and resident expatriates have been reported.
Treatment with corticosteroids and praziquantel has
been less than dramatic and a prolonged course followed
by recovery must be anticipated.
Filariasis. In Thailand, filariasis is caused by two types
of microfilaria: Brugia malayi and nocturnal subperiodic
Wuchereria bancrofti.53 Brugia timori was not reported in
Thailand. B. malayi exists in the south, whereas the
others are present in the area between the border of
Thailand and Myanmar, from Mae Hongsorn to
Ranong. Six species of Mansonia and 4 species of Aedes
are the main mosquito vectors for Brugia and Wuchereria filariasis, respectively. Culex mosquitos also transmit
Wuchereria in Myanmar.54 The incidence of positive
rate for microfilaria (MF) has decreased since 1961
from 6% to less than 1% in 1992. The prevalence in
endemic regions of positive MF by the use of thick
blood films ranged from 0.1% to 2.2% in 1994. A total
199
of 1,252 cases were reported in 1997, with a prevalence
of approximately 2/100,000. The standard treatment is
diethylcarbamazine for 21 days or a single dose of ivermectin 150 mg/kg. Filariasis should pose no risk for travelers to Thailand.
Trematodes. Opisthorchiasis. The native population along
the Mekong River has a tradition of eating raw pickled
fish. Infestation with Opisthorchis viverrini, a small fluke
that lives in the biliary tract, is almost universal in many
villages of the northeast. Heavy and prolonged carriage
can cause chronic cholangitis, calculi, and ultimately
cholangiocarcinoma. The reported incidence of
cholangiocarcinoma in an endemic province (Khon
Kaen) is 84.6 and 36.8/100,000 in males and females
respectively.55 The drug of choice, praziquantel, is readily
available in country. An opisthorchiasis control program
in northern Thailand has had an impact on the infection
rate, which has markedly decreased.56 This parasite should
present no significant risk to the traveler who is unlikely
to experiment with raw fresh water fish.
Fascioliasis. Fasciola gigantica, Fasciola hepatica, and Fascilopsis buski are the three main flukes which can cause
human fascioliasis.57 F. gigantica is the most common
reported species. Fascioliasis is caused by ingestion of water
vegetables contaminated with metacercaria. The patients
often present with prolonged fever with hepatomegaly
in the presence, or absence, of eosinophilia. The first case
in Thailand was reported in 1967, with the highest
prevalence in the northeast.58,59 To date, there have been
at least 30 cases reported to the MPH. Surgical removal
is the treatment of choice, since no specific drug for this
trematode is available. These flukes should not pose a risk
to the average traveler.
Lung Flukes (Paragonimiasis). Six species of Paragonimus
are present in Thailand, but only two (Paragonimus westermani and Paragonimus heterotremus) are able to cause
human disease.60,61 P. westermani is present in pockets in
Pittsanulok, Kampang Peth, SukhoThai, etc. It has a
complicated life cycle involving fresh water crabs and
humans. The clinical picture is characterized by hemoptysis, fleeting pulmonary infiltrations, and pleural effusions. Patients are often treated first for tuberculosis until
characteristic ova are found in sputum, pleural fluid, or
stool. Treatment with praziquantel is effective. Paragonimiasis was first reported in Thailand in 1928, but now
the incidence has markedly decreased. The disease is an
unlikely hazard for travelers who do not eat uncooked
or poorly cooked fresh water crustaceans.
Echinostomiasis. Echinostoma malayanum, Echinostoma revolutum, Echinostoma chinatum, Echinostoma ilocanum, and
200
J o u r n a l o f Tr a v e l M e d i c i n e , Vo l u m e 8 , N u m b e r 4
Hypoderaneum conoideum are present in Thailand, with
the most common species being E. malayanum.62,63 The
life cycle involves snails, fish, and tadpoles. The prevalence sometimes exceeds 50% in some areas of northern Thailand. Clinical symptoms of echinostomiasis
include abdominal pain, violent watery diarrhea, and
anorexia. Infections are associated with common sociocultural practices of eating raw or insufficiently cooked
mollusks, fish, crustaceans, and amphibians, promiscuous defecation, and using night soil (human excrement
collected from latrines) for fertilization of fish ponds. No
specific treatment is available.
cases, and 49 of 57 cases, reported in 1992, and 1993,
respectively, were in AIDS patients.
Histoplasmosis. Histoplasmosisis, caused by Histoplasma
capsulatum, is also common in AIDS patients. Most cases
were reported in central and northeast Thailand.
Penicilliosis. The disease is caused by Penicillium marneffei.
Disseminated penicilliosis is the third most common AIDSdefining infection in Thailand.66 The highest incidence is
observed in the north, since 19.4% of wild bamboo rats
(Cannomys badius),and 75% of hoary bamboo rats (Rhizomys
pruinosus) in the central plain, carry the fungus. The first
case was reported in 1984, and was in a normal host.67
Cestodes. Cysticercosis and Taeniasis. Cysticercosis is
Poisonous Animals and Fishes
acquired by ingesting Taenia solium eggs shed in human
feces, whereas taeniasis is caused by ingesting
undercooked pork contaminated with Taenia solium
larvae. Taeniasis is also caused by ingesting undercooked
beef contaminated with T. saginata larvae. After ingestion
of the eggs, the oncospheres are released, penetrate the
intestinal mucosa, and migrate throughout the body,
resulting in cysticercosis. Larval cysts are found in
nearly every tissue, but mature forms are fully developed
in the central nervous system, skeletal muscle,
subcutaneous tissue, and within eyes. Patients are
asymptomatic for several years before the onset of
symptoms, which usually manifest as seizures. Treatment
is praziquantel 50 mg/kg/day for 15 days, or
albendazole 15 mg/kg/day for 8 days. It is of no use
if the cyst is dead and calcified. Since neurocysticercosis
is not a reportable disease, the total number of cases
diagnosed is not known but the highest prevalence is
observed in northeastern Thailand.
In Thailand, 175 species of snakes have been identified, of which 85 are venomous.68,69 Only a few present a hazard to man. Important tissue and hematotoxic
vipers are: Russell’s viper, Malayan pit viper, and several
species of green pit vipers, of which Trimeresurus albolabris
is the cause of the majority of human bites. This snake
can be found in Bangkok’s gardens, as well as throughout most of the country. Among neurotoxic snakes,
there are 3 species of Siamese cobras: Naja kaouthia
(Monocled cobra), Naja siamensis (Siamese spitting cobra),
and Naja sumatrana, also known as the golden spitting or
southern spitting cobra. The giant king cobra (Ophiophagus hannah) belongs to a different genus and is now
an almost endangered species. Cobra bites cause respiratory paralysis and also inject a potent tissue toxin.
Kraits seen in Thailand are Bungarus fasciatus (Banded
krait), Bungarus candidus (Malayan krait), and Bungarus flaviceps (Red headed krait). They all have potent neurotoxins
but inflict almost painless bites, with little if any local reaction, in contrast to the cobras. There are also several species
of sea snakes that have potent neurotoxins and can cause
renal failure due to myoglobinuria. They only very rarely
attack humans. Antivenoms against important local snakes
are manufactured by the Thai Red Cross, and virtually
all private and government hospitals have experience in
dealing with snake bite cases. The most common cause
of snakebite is when the victim attempted to capture the
snake. Snakebite should not be a significant hazard to the
average traveler. The MPH reported 8,435 cases of
snakebites and less than 20 fatalities in 1995.
The tropical waters around Thailand contain a variety of venomous cone shells and spiny fish, which are difficult to identify for the layperson. Fatalities are, however,
uncommon. A large variety of jellyfish are also found,
and most can produce moderately severe skin eruptions.
There has been one report of a fatal contact with a box
jellyfish on Koh Samui in 1999, and it is certain that Chironex fleckeri is present in Thai waters. Box jellyfish do
not like sun and stay in deeper waters during the day, coming closer to the surface in the evening and at night. There
Sparganosis. The sparganum, or pleurocercoid, is a solid
larval tapeworm belonging to the genus Spirometra. Its first
and second intermediate hosts are Cyclops, and frogs or
snake. Humans acquire sparganosis by ingesting Cyclops
infested with procercoid larva, which penetrate the
intestinal wall and become encysted as sparganum in any
organ, particularly the orbit and subcutaneous tissue.
The incidence of this infection is as frequent as gnathostomiasis. The disease also is acquired by ingesting raw frogs
or snakes containing sparganum or by applying the flesh
of frogs to wounds and sore eyes as a form of indigenous
medicine. Surgical removal is the treatment of choice since
no specific drug for this cestode is available. The first
reported case in Thailand was in 1943, and there are now
at least 30 known cases.64,65
Fungal Diseases
Cryptococcosis. Cryptococcus neoformans is the causative
agent of cryptococcosis. Cryptococcosis is often
encountered in AIDS patients. As an example, 27 of 30
Suankratay et al., Thailand: Country Survey
have been two known fatal shark attacks in the Gulf of
Siam. One occurred some 40 years ago near Sriracha, and
the last one occurred 2 years ago off Koh Phangan, Sura
Thani Province south of Bangkok. Large sharks are common on the Andaman (Indian Ocean) side. There are no
salt-water crocodiles in Thailand, and the fresh water varieties are now confined to crocodile farms.
Migration and Immigration Problems
Thailand has had a model birth control program (present population growth rate 1.1%). This, and an improving living standard,have resulted in labor shortages in some
industries (construction, fisheries, servants, etc.). Both legal
and illegal foreign workers can be found throughout the
country. Most come from Myanmar, Laos, China,
Bangladesh, and Cambodia. This has resulted in the
occasional introduction of diseases that have been virtually eradicated in Thailand (schistosomiasis from Cambodia, kala azar from Bangladesh, etc.). The ethnic
conflicts and an aggressive government in Myanmar
have created refugee camps along the border. There is a
continuing struggle by authorities and humanitarian
organizations to suppress the thriving trade in young
females who are lured into the country for prostitution,
mostly from Myanmar, China, Laos, and Cambodia. The
indigenous, quite homogeneous Thai population has
not been subject to much religious or ethnic conflict.
However, there was a significant movement from rural
Thailand to the cities during the past economic boom
years. This was reversed when factory and construction
workers lost their jobs and moved back to their villages.
Since Thailand is a producer and major exporter of surplus food, the return to farm life was not overly traumatic.
List of Local Resources
Hospital Facilities
There are several fully equipped and well-staffed private hospitals in Bangkok that are recommended by foreign embassies and regularly used for primary, secondary,
and most tertiary care. They also act as medical referral
centers for patients from neighboring countries. Major
medical and surgical specialties are available at all of them
and so are good laboratory, x-ray, and scanning facilities (computed tomography and magnetic resonance
imaging). However, it is best if a traveler in need first
contacts his local hosts, embassy, or the International
Travel Clinic (BNH Hospital [622-632-0570]) for referrals, as some nationalities prefer one or the other hospital for better communication reasons (some have
Japanese-, German-, Chinese-, and French-speaking
staff). Chieng Mai, Khon Khean, Udorn, SogklahHadyai, Phuket, Pattaya, and Rayong also have very
201
adequate medical facilities that can handle primary and
most secondary care problems.
The American, French, Russian, and Japanese
embassies in Bangkok have medical officers on their
staff who can also provide referrals for their nationals.
Other embassies have appointed local medical advisors.
The United Nations (ESCAP) has a medical unit that
can provide services to UN employees.The US Army’s
Walter Reed Institute maintains a joint research facility
with the Thai Army in Bangkok. Oxford University,
jointly with the Wellcome Foundation, has several British
expatriate researchers based in Bangkok. Many European,
American, Japanese, and Australian universities have biomedical research and student exchange programs with
Thai medical colleges.
Pharmaceuticals and vaccines are readily available
throughout the country and of good quality. Cold chain
and potency of vaccines are being monitored by the MPH
using World Health Organization standards. Travelers in
need of medications are,nevertheless,advised to go to one
of the hospital pharmacies or one recommended by Thai
friends or your embassy. Drugs and vaccines are generally
less expensive than those in Europe or North America.
Other Resources
Queen Saovabha Memorial Institute (Thai Red Cross Society).
1871 Rama IV Road, Bangkok. This facility operates a
snake farm (with daily lectures and demonstrations in
English and Thai), an animal bite clinic, an anonymous
STD clinic, and HIV counseling center, as well as
immunization facilities for local residents and travelers.
There is a bulletin board “Travelers Advisory,” the lists
current health hazards and preventive medicine
recommendations for tourists.
International Travel Medicine Clinic. BNH Hospital,Convent
Road, Bangkok (Tel 632-0570). This clinic provides all
routine and tropical vaccinations, is connected to an
international travel medicine computer database, and
can provide referral advice and counseling regarding
health-related matters.
Acknowledgments
This essay was written at the request of the Journal
of Travel Medicine by Dr. Chusana Suankratay and Professor Henry Wilde. The Global Infectious Disease and
Epidemiology Network database of Professor Stephen
Berger was also used.
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