8: Diagnostic Dilemmas


CHAPTER 8
Diagnostic Dilemmas


Presented below are seven challenging cases in diagnostic parasitology. Case scenarios are based on information and specimens provided to the veterinary diagnostician. The answers to these diagnostic dilemmas are available on the accompanying website www.wiley.com/go/zajac/parasitology to this volume.


Diagnostic Dilemma 1


A 2.5‐year‐old neutered male, indoor/outdoor American bulldog family pet presented in Scranton, PA for an annual wellness exam. The dog had been dewormed monthly and was currently on prevention for heartworm, intestinal helminths, fleas, and ticks. During preparation of the fecal flotation, the veterinary technician noted a small (~5 mm) organism in the fecal material and suspected it might be a worm of some kind. What is the identification of this specimen?

Photo depicts the specimen observed in the fecal material of a dog. The specimen was approximately 5 mm in length.

Fig. 8.1 Specimen observed in the fecal material of a dog. The specimen was approximately 5 mm in length.


Photo courtesy of Dr. Manigandan Lejeune, Animal Health Diagnostic Center, Cornell University, Ithaca, NY.


Diagnostic Dilemma 2


A 4‐year‐old mixed breed neutered male dog was presented in Jonesboro, Arkansas for annual physical examination and vaccination. The dog was not on heartworm preventive and had an intermittent cough. A blood sample was negative for heartworm antigen on a well‐validated commercial test. Numerous microfilariae were found on microscopic examination of a saline wet mount. Whole blood was submitted for Knott’s test, which confirmed the presence of Dirofilaria immitis microfilariae based on morphologic appearance, size, and nuclear staining (Figs. 8.2, 8.3).


What is the most likely explanation for a negative heartworm antigen test in the face of numerous Dirofilaria immitis microfilariae in this dog?

Photo depicts Dirofilaria immitis microfilariae recovered on Knott’s test from an infected dog. The identification of D. immitis is supported by the presence of numerous microfilariae in the sample.

Fig. 8.2 Dirofilaria immitis microfilariae recovered on Knott’s test from an infected dog. The identification of D. immitis is supported by the presence of numerous microfilariae in the sample (see Table 3.2).

Photo depicts the higher magnification view of a single Dirofilaria immitis microfilaria. Although individual microfilaria will shrink in formalin over time, when first prepared, D. immitis microfilaria recovered on a Knott’s test usually measure 295–325 μm long by 5–7.5 μm wide.

Fig. 8.3 Higher magnification view of a single Dirofilaria immitis microfilaria. Although individual microfilaria will shrink in formalin over time, when first prepared, D. immitis microfilaria recovered on a Knott’s test usually measure 295–325 μm long by 5–7.5 μm wide.

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Sep 19, 2022 | Posted by in GENERAL | Comments Off on 8: Diagnostic Dilemmas
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