Abstract
BackgroundDetection of D. immitis microfilaria (mf) is an important diagnostic skill in veterinary medicine and is critical to Day 1 veterinarians and technicians. Finding a supply of blood containing mf to teach the technique and formalin’s adverse environmental effects used in the diagnostic microscopic tests present a challenge.ResultsThis study evaluated the use of cryopreserved and recently drawn mf-infected blood along with two fixative reagents, acetic acid or formalin for mf detection. The specific aims included determining if veterinary students could 1) detect cryopreserved mf added to fresh blood using routine diagnostic testing and 2) detect morphological differences in the mf. The 236 students were kept blind from the sample status. The ability of the students to identify mf and the mf morphology were compared for the samples and fixatives evaluated. The results demonstrate using a combination of cryopreservation and acetic acid for teaching microfilaria diagnostic techniques is fleasible; however, the quality of the mf morphology is less than optimal when compared to freshly acquired mf containing blood. Compared to reference values, the mf demonstrated a decrease in size with each additional variable evaluated.ConclusionA majority (98.3%) of the 236 students correctly identified the presence of mf. Teaching laboratories could utilize cryopreserved mf-spiked donor blood in lieu of freshly collected mf-containing blood from a naturally or experimentally infected dog. Substitution of less hazardous chemicals for the fixative can be used. Finally, the change in size measurements provides a mechanism to ensure students can correctly measure mf as students are required to do verifiable measurements and cannot copy reference values from a text book since the cryopreservation and fixation methods cause the mf to measure smaller than textbook reference values.
Highlights
Detection of D. immitis microfilaria is an important diagnostic skill in veterinary medicine and is critical to Day 1 veterinarians and technicians
Year 1 evaluating fleasibility of cryopreservation and spiking donor blood The mf that were recovered on days 0, 7, 21, and 70 day remained above 897 mf per 50 ul of Modified Knott’s test (Table 1)
It must be considered that the students are inexperienced with viewing the distinctive morphology of the D. immitis mf, and this was the first time the students performed these techniques in the teaching laboratory to view the mf microscopically
Summary
Detection of D. immitis microfilaria (mf) is an important diagnostic skill in veterinary medicine and is critical to Day 1 veterinarians and technicians. In 2018, the Companion Animal Parasite Council compiled 143,492 cases of heartworm disease in dogs. The competency of veterinarians and technicians to perform these tests and recognize mf is reliant on the teaching of the techniques during their clinical laboratory skills education. Often a supply of D. immitis mf infected blood can be difficult to obtain when scheduled to teach these diagnostic skills. Successful cryopreservation of D. immits mf would allow instructors to have a stock of mf in the laboratory freezer for teaching purposes, without having to obtain recently drawn “fresh” mf containing blood in sufficient volume when students want to practice diagnostic techniques
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