CAPSULES
The Kissing (Bug) Disease
Trypanosoma cruzi is a protozoan
parasite known to infect humans,
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wildlife, and dogs. Infection occurs
when hematophagous triatomines (kissing bugs) bite hosts and
bugs’ feces enter bite sites or mucous membranes. In humans,
this causes Chagas disease. Symptoms of T cruzi infection in
humans and dogs include acute myocarditis, chronic heart disease, and sudden death; infection can also be asymptomatic.
Study authors examined the seroprevalence of T cruzi in dogs
from 7 Texas shelters. There are enzootic cycles involving
infected wildlife reservoirs and domestic dogs across the southern United States; dogs in Texas are at high risk. A total of 205
blood samples were taken, and T cruzi exposure was determined using the Chagas STAT-PAK, a rapid immunochromatographic test. Of those, 18 dogs tested positive, which makes the
overall seroprevalence 8.8%. For individual shelters, prevalence ranged 6.7% –13.8%.
however, the importance of dogs as a reservoir host has not
been studied in the United States. Further research is needed
to evaluate the association between exposure of shelter dogs to
T cruzi and the risk for Chagas disease in humans.
Commentary
This study sought to detect the presence of anti-T cruzi antibodies in a population of shelter dogs from Texas. Blood samples were also examined for parasite DNA by 2 PCR methods.
No significant differences in seropositivity were noted with
regard to location, sex, age, breed, or adoption history. Shelter
dogs are a useful population to examine the occurrence of T
cruzi infection as an indication of potential risk to humans and
owned dogs. Local exposure was likely in these cases as seropositivity was not biased by location or age of the animal, and
some of the shelters were in regions where kissing bug vectors
are well-established.—John J. Schaefer, DVM, MS, PhD, DACVM
Source
Because of shelter dogs’ widespread exposure to T cruzi, these
dogs could act as sentinels for assessing transmission risk;
Shelter dogs as sentinels for Trypanosoma cruzi transmission across Texas,
USA. Tenney TD, Curtis-Robles R, Snowden KF, Hamer SA. EMERG INFECT DIS
20:1323–1326, 2014.
Diagnostic Value of Lymph Node FNA
Lymph node (LN) cytology is an accessible,
inexpensive test with good sensitivity and
specificity, albeit with intrinsic limitations. This retrospective
study aimed to describe common indications for LN fine needle
aspirates (FNA) and reported cytological diagnoses as well as
frequency and explanations for nondiagnostic samples from
dogs and cats. FNA sample records were evaluated for sampling, sample quality, diagnosis achieved, and reason for
nondiagnostic samples. It was hypothesized that samples
with clinical history provided and greater number of slides
submitted would increase likelihood of diagnosis.
In the 1473 records reviewed, the most common reasons for
aspirate submission were investigation of lymphadenopathy or
tumor staging. In dogs, 72.8% of samples were diagnostic; in
cats, 85.9%. In dogs, the most common diagnosis was lymphoma, followed by reactive hyperplasia. In cats, most common
was reactive hyperplasia, followed by lymphoma; however, only
50% of these lymphoma cases were confidently diagnosed,
compared with 73% in dogs. The most common causes of nondiagnostic samples were absence of nucleated cells, cell disruption, and low cell yield. Submission of clinical history did not
correlate with likelihood of reaching diagnosis. In dogs, submission of a higher number of slides was correlated with a
higher likelihood of a diagnostic sample and cytological diagnosis. Educating practitioners on improved sample collection,
smearing technique, and in-house sample examination before
submission may increase diagnostic value of LN FNA.
Global Commentary
This study, which involved submission of nonstained samples
with the standard staining in the laboratory, clearly demonstrates that LN cytology is highly diagnostic. Nondiagnostic
samples were the result of either sampling or smear-preparation
technique. In most clinical settings, slightly more nondiagnostic
samples may be expected because of poor staining. There is no
reason, however, to consider that the LN cytology is of low
diagnostic yield. If the result is nondiagnostic because of the
sample preparation, a clinician can repeat the procedure for
better sampling. If it is nondiagnostic because of the nature of
the lesion, the clinician can turn to surgical resection and histopathology. This is a low-risk, high-return procedure.—Takuo
Ishida, DVM, PhD, DJCVP (Japan)
Source
The diagnostic utility of lymph node cytology samples in dogs and cats.
Amores-Fuster I, Cripps P, Graham P, et al. J SMALL ANIM PRACT 56:125–129,
2015.
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May 2015 • Clinician’s Brief 53