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DIFFERENTIAL SLIDES LEGEND
CYCLE 39 SLIDE 3
PARASITIC DISEASE
A parasitic disease is an infectious disease caused or transmitted by a parasite. A parasite is an organism
that lives on or in a host organism and gets its food from or at the expense of its host. Many parasites do
not cause disease. Parasitic diseases can affect practically all living organisms, including plants and mammals.
The study of parasitic diseases is called parasitology. Some parasites like Toxoplasma gondii and Malaria can
cause disease directly, while other organisms can cause disease by the toxins that they produce.
Although organisms such as bacteria function as parasites, the usage of the term “parasitic disease” is
usually more restricted. The three main types of organisms causing these conditions are protozoa (causing
protozoan infection), helminths (helminthiasis), and ectoparasites. Protozoa and helminths are usually
endoparasites (usually living inside the body of the host), while ectoparasites usually live on the surface of
the host. Occasionally the definition of “parasitic disease” is restricted to diseases due to endoparasites.
Protozoa
Protozoa are microscopic, one-celled organisms that can be free-living or parasitic in nature. They are able
to multiply in humans, which contributes to their survival and also permits serious infections to develop from
just a single organism. Transmission of protozoa that live in the human intestine to another human typically
occurs through the faecal-oral route. The protozoa that are infectious to humans can be classified into four
groups based on their mode of movement:
 Sarcodina – The amoeba, e.g. Entamoeba
 Mastigophora – The flagellates, e.g., Giardia, Leishmania
 Ciliophora – the ciliates, e.g., Balantidium
 Sporozoa – organisms whose adult stage is not motile e.g. Plasmodium, Cryptosporidium
Leishmaniasis
Leishmaniasis is a vector-borne disease that is transmitted by the bite of sand flies and caused by obligate
intracellular protozoa of the genus Leishmania. The distribution is world-wide, but 90% of cutaneous
Leishmaniasis cases occur in Afghanistan, Algeria, Iran, Saudi Arabia, Syria, Brazil, Columbia, Peru and
Bolivia. Many Leishmanial species infect animal as well as humans. Human infection is caused by about 21 of
30 species that infect mammals. Leishmaniasis includes two major diseases, cutaneous Leishmaniasis and
visceral Leishmaniasis, caused by more than 20 different Leishmanial species.
Thistle QA is a SANAS accredited organisation, No: PTS0001 Accredited to ISO guide 43 and ILAC G13 Certificate available on request or at www.sanas.co.za P.O. Box 131375, Bryanston, 2074 Ground Floor, Block 5 Bryanston Gate, 170 Curzon Road Bryanston, Johannesburg, South Africa 804 Flatrock, Buiten Street, Cape Town, 8001 www.thistle.co.za Tel: +27 (011) 463 3260 Fax: +27 (011) 463 3036 Fax to Email: + 27 (0) 86‐538‐4484 e‐mail : [email protected] The most common form of Leishmaniasis is localized cutaneous Leishmaniasis, which usually appears as one or
more painless ulcers. Visceral Leishmaniasis is a febrile illness with weight loss, enlargement of the spleen
and liver, and decreases in the production of blood cells that can lead to anaemia, bleeding and infections
with other microorganisms.
Without treatment, this form of the disease is nearly always fatal.
Mucocutaneous Leishmaniasis is a rare form of the disease that can occur months or years after the healing
of a cutaneous Leishmaniasis ulcer. This form of the disease can affect the nasal septum, palate and other
parts of the nasopharynx.
The diagnosis of cutaneous Leishmaniasis relies on the demonstration of Leishmania in tissue biopsy, scraping
or impression preparations by microscopy and/or culture in a specialized medium. Species identification is
recommended because management may vary depending on the infecting species. Recently, assays based on
the use of polymerase chain reaction (PCR), including multiplex assays that can distinguish among several
species simultaneously, have become more widely available.
Bone marrow biopsy specimen from a patient with visceral Leishmaniasis showing a
macrophage containing Leishmania amastigotes.
For visceral Leishmaniasis, definitive diagnosis requires the demonstration of the parasite by smear or
culture in tissue, usually bone marrow or spleen, and thus entails an invasive procedure. Splenic aspirate has
the highest sensitivity of available tissue sampling techniques, but carries a risk of serious hemorrhage. Bone
marrow aspirates are safer, but have substantially lower sensitivity. Parasites can be detected in tissue
samples by light microscopy of stained slides, culture in a specialized medium, or by specific PCR assays.
Serological tests (immunofluorescent antibody tests or enzyme linked immunosorbent assays) can be used to
demonstrate anti-Leishmanial antibodies. These assays have high sensitivity for visceral Leishmaniasis in
patients without HIV infection, but may show positive results due to subclinical infection or cross-reactions,
and are therefore less specific than tissue sampling. Among patients with HIV-visceral Leishmaniasis co
infection, the sensitivity of serology was low; parasitological diagnosis is advisable. The introduction of
point-of-use antibody-detection tests has improved prospects for diagnosis in remote settings, but the
sensitivity of available tests appears to vary by geographic region.
References
1. http://www.cdc.gov/parasites/leishmaniasis/disease.html
2. http://en.wikipedia.org/wiki/Parasitic_disease Questions
1. Discuss the term Parasitic Disease.
2. Discuss the Protozoa and its classification.
3. Discuss the diagnosis of Leishmaniasis.
Thistle QA is a SANAS accredited organisation, No: PTS0001 Accredited to ISO guide 43 and ILAC G13 Certificate available on request or at www.sanas.co.za