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Did you know? Pregnancy-associated IMHA in dogs and cats.

Immune-mediated hemolytic anemia (IMHA) represents one of the most common immune-mediated diseases encountered in dogs. As suggested by the more limited literature on the topic of feline IMHA, cats (originally at least), appeared to have a lower prevalence of the disease when compared with dogs. However, more recent studies have suggested higher numbers of cats with IMHA in populations investigated further for their anemia.


Regardless of the prevalence of IMHA in the different species, it remains a potentially life-threatening disease. Also, like with most immune-mediated diseases, the exact trigger remains to be determined or is poorly understood. In this blog post, we'll talk a bit about another potential mechanism or associated cause for this disease, pregnancy-associated IMHA.



Below are a list of the currently recognized causes for IMHA in dogs and cats, respectively.


Potential causes for IMHA in dogs include:


Primary/idiopathic

Secondary:

Infectious diseases (piroplasms - particulary Babesia gibsoni; Anaplasma species

Inflammatory diseases

Neoplasia

Drugs/toxins

Vaccination


Potential causes for IMHA in cats include:


Primary/idiopathic

Secondary:

Infectious diseases (Mycoplasma haemofelis, coronavirus, retroviral infections, Babesia felis)

Inflammatory diseases (pancreatitis)

Neoplasia (lymphoma)

Drugs/toxins (acetaminophen, propylthiouracil, methimazole, famotidine)

In humans, pregnancy-associated IMHA has been well-described, with an estimated prevalence of one in 50,000 pregnancies (ranging from 5.4% to >80% depending on geographical distribution). In fact, pregnancy-associated IMHA is considered more common than IMHA in the non-pregnant population. Disease severity can vary from gradual, compensated disease to rapid-onset, life-threatening anemia. Typically, human patients present in the third trimester and show improvement in the degree of anemia following delivery (+/- some steroid use).


The exact mechanism as to why pregnancy-associated IMHA happens in humans is poorly understood. Feto-maternal microtransfusion has been proposed, however, this is speculative. It is believed that fetal cells possessing paternal antigens are at fault, and elicit an immunologic response in the mother following microtransfusion.


Potential mechanisms that were discussed in the case reports below include:


Feline case: fetuses were of either feline blood group/type A or AB, and the queen was of type B with naturally occurring anti-A alloantibodies. Exposure to type A blood (from the fetus) in the queen would have led to significant hemolysis and hemagglutination.




Take-home message:


If you have a dog or a cat present to you in late-term pregnancy demonstrating signs and blood work findings consistent with a diagnosis of IMHA, don't forget to consider the possibility of pregnancy-associated IMHA, before jumping for those miraculous steroids.


References:


Fernandez Y, Sharman MJ, Seth M. (2020) Pregnancy-associated immune-mediated hemolytic anemia in a dog. J Vet Emerg Crit Care, 30(3):308-311.


Garden OA, Kidd L, Mexas AM, et al. (2019) ACVIM consensus statement on the diagnosis of immune-mediated hemolytic anemia. J Vet Intern Med, 30(2):313-334. Available online:

https://onlinelibrary.wiley.com/doi/full/10.1111/jvim.15441


Kohn B, Weingart C, Eckmann V, et al. (2006) Primary Immune-Mediated Hemolytic Anemia in 19 Cats: Diagnosis, Therapy, and Outcome (1998-2004). J Vet Intern Med, 20:159-166. Available online: https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1939-1676.2006.tb02836.x?sid=nlm%3Apubmed


Kopke MA, Pemberton S, Ruaux CG. (2019) Presumed immune-mediated haemolytic anaemia associated with pregnancy in a cat. JFMS Open Rep, 2019;5(1):2055116919841689. Available online: https://journals.sagepub.com/doi/full/10.1177/2055116919841689

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