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Veterinarians and Emerging Competencies with Hemoparasite Testing

January 23, 2023

Your canine patient from the northeast United States presents febrile, limping, and on no tick preventatives. You think, “I am going to do a blood smear for this patient.” (along with the rest of the work up). You swear you see the glimmer of a small circular morulae in a neutrophil, and so does your colleague. As soon as you think, ”Oh man, this is it, I think I found a hemoparasite,” 

Your world is crushed, when you find out that in fact it wasn’t what you thought. However, you wait patiently for the next case where maybe that time you will reach your goal of finally locating a hemoparasite. 

Obtaining a definitive diagnosis via microscopic identification of a hemoparasite is on the bucket list of most veterinarians and technicians. However, locating one is a rare occurrence as significant limitations exist during the day to day of clinical practice. 

If this hemoparasite treasure-finding story seems all too familiar, it is because hemoparasite detection is difficult for a variety of reasons. 

Is case selection an issue? No ruler on the microscope? Negative amounts of time to do a direct smear? What if two different disease hemoparasites look very similar? Many factors can get in the way of a positive hemoparasite detection, including the variables below.

Minimal Guidance

Information is spread amongst multiple textbooks with maybe one perfect photo of the hemoparasite. That perfect photo is beautiful to observe, however this single reference does not always reflect the appearance in every patient. Inclusion body disease (IBD) in snakes is unfortunately common. Although PCR tests are available to identify this pathogen, a presumptive diagnosis of IBD is based on the identification of intracytoplasmic inclusions in one or more cell lines. 

An example of a perfect image veterinarians might see in a textbook versus what can be seen elsewhere captured at a lab is displayed below. Both photos show evidence of inclusion body disease in boa constrictors; the first is clear, whereas the second isn’t as obvious. The first photo also uses a different stain versus what is classically used elsewhere.

Boa constrictor. IBD. Peripheral blood film with an erythrocyte (arrow) and lymphocyte (arrowhead) containing eosinophilic-staining inclusions. H&E stain. Chang, Li-Wen & Jacobson, Elliott. (2010). Inclusion Body Disease, A Worldwide Infectious Disease of Boid Snakes: A Review. Journal of Exotic Pet Medicine. 19. 216-225. 10.1053/j.jepm.2010.07.014
Boa constrictor. IBD. Peripheral blood film with an erythrocyte (arrow) containing an IBD inclusion. Wright-Giemsa stain. Image taken from Moichor laboratory.

Just when you think you have all the information you need, you realize that there are some hemoparasites that look, act, and stain differently at different points in their life stage. Not only are examples of these not efficient to locate, but a single hemoparasite may even vary in appearance based on its individual species. Leukocytozoan is a commonly encountered hemoparasite in birds of prey. Depending on the species infecting the animal and its life stages, it can look very different microscopically. 

Leukocytozooan Mature macrogrametocyte (arrow) and microgametocyte (arrowhead) of L. californicus; Nardoni S, Parisi F, Rocchigiani G, Ceccherelli R, Mancianti F, Poli A. Haemoproteus spp. and Leucocytozoon californicus Coinfection in a Merlin (Falco colombarius). Pathogens. 2020 Apr 4;9(4):263. doi: 10.3390/pathogens9040263. PMID: 32260378; PMCID: PMC7238121.

Lack of appropriate technology

Whether it’s funding or awareness, the veterinary technology on hand can play a role in locating hemoparasites. Microscopes in particular are an important consideration as microscope technology varies greatly, and often in-clinic microscopes are not as advanced or maintained as they would be in a clinical pathology lab. Additionally, core knowledge regarding microscopy is poor for most veterinarians. A common way pathologists will start their day is by setting up their microscope. Kholer illumination is a method that requires properly adjusting the light path to achieve ideal image contrast and resolution.

https://www.olympus-lifescience.com/en/discovery/how-to-align-khler-illumination-in-6-simple-steps/

Where to look

Limited exposure to the finer details of sample assessment in veterinary school results in vets and technicians alike employing a less optimal staining technique or picking the wrong part of the sample to assess.

  • Spinning the blood and examining the serum just above the buffy coat can improve the identification of diseases like Trypanosoma and microfilariae
  • Examining a smear of the buffy coat can improve the ability to identify haemoproteus and leukoocytozoon

Artifact staining (maybe is real, maybe it’s maybelline)

What is real, and what isn’t? Being able to tell the difference between a hemoparasite and an artifact requires specialty level knowledge and a high case exposure. For example, the age-old problem of identifying the difference between Mycoplasma felis and staining artifact can cause confusion.

Picture of staining artifact with blue arrows. Mycoplasma felis outlined by black arrows. (From the university of kansas vet lab).

Often, seeing stain precipitate in the background will alert the reader that staining artifacts may be present, but what if there is disease in that sample too? Proper stain maintenance and following in-hospital staining protocols can help reduce precipitates that can complicate detection.

Working in partnership with animal reference laboratories

Identifying hemoparasites can be directly beneficial to clinical decision making even though it can be challenging and possibly time consuming. The more time spent refining and building a knowledge base around hemoparasite identification, the more successful attempts at identification will be. 

However, working with a laboratory that offers free veterinary pathology reviews can help veterinarians confirm findings. For example,  all CBC results at Moichor include cell count and cell morphology along with comments on hemoparasite presence by a board-certified clinical pathologist. Additionally, images of all cells and associated morphology are available on the Moichor portal for all CBC results. This offers both an opportunity for knowledge advancement while knowing that a full hematology profile is available for every patient. 

Wondering what kind of hemoparasite testing Moichor can offer? Download our test menu to see pricing, diagnostics turnaround times, requirements, and more.

References: 

  1. Nardoni S, Parisi F, Rocchigiani G, Ceccherelli R, Mancianti F, Poli A. Haemoproteus spp. and Leucocytozoon californicus Coinfection in a Merlin (Falco colombarius). Pathogens. 2020 Apr 4;9(4):263. doi: 10.3390/pathogens9040263. PMID: 32260378; PMCID: PMC7238121.
  2. Chang, Li-Wen & Jacobson, Elliott. (2010). Inclusion Body Disease, A Worldwide Infectious Disease of Boid Snakes: A Review. Journal of Exotic Pet Medicine. 19. 216-225. 10.1053/j.jepm.2010.07.014.
  3. Kastl, Brandy, and Nora Springer. “Fake out! Hemoparasite or Blood Smear Artifact.” FAKE OUT! Hemoparasite or Blood Smear Artifact?, https://www.ksvdl.org/resources/news/diagnostic_insights_for_technicians/october2020/hemoparasite-or-blood-smear-artifact.html. 
  4. Alvarenga, Lauren. “How to Align Köhler Illumination in 6 Simple Steps.” How to Align Köhler Illumination in 6 Simple Steps | Olympus LS, 3 Feb. 2022, https://www.olympus-lifescience.com/en/discovery/how-to-align-khler-illumination-in-6-simple-steps/. 

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Veterinarians and Emerging Competencies with Hemoparasite Testing

Developing competency with hemoparasite testing is important for veterinarians. Learn what gaps in knowledge emerging veterinarians may face when it comes to accurately spotting and identifying relevant hemoparasites.

January 23, 2023
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