Myocarditis is a relatively rare disease of dogs and cats. In myocarditis, the muscle tissue (myocardium) of the heart develops inflammation and starts to degenerate. The amount of connective tissue in the heart increases and pumping blood to the body becomes more difficult. The animal’s ability to conduct vital functions is impaired.
The signs of myocarditis are similar to cardiomyopathy: the animal is weak, depressed, and possibly febrile. Fluid accumulation in the lungs and abdomen is possible. Other signs include cough, difficulties in breathing, as well as arrhythmias, and heart murmurs.
The etiology of myocarditis is diverse. Possible causes are certain viruses, bacteria, fungi, and protozoa, as well as some toxins, traumas, and autoimmune diseases. The canine parvovirus and the West-Nile virus are known to be able to cause myocarditis. Borrelia burgdorferi, a bacterium causing Lyme disease, and Trypanosoma cruzi -protozoa, causing Chaga’s disease, may also lead to the inflammation of the heart muscle. Deficiencies in certain minerals and vitamins, such as selenium and vitamin E, can lead to the degeneration of the myocardium.
In 2019, M.A. Ernandes with her colleagues published a report, where coronavirus was found to be the cause of myocarditis in a longhaired, domestic cat. With the COVID-19-pandemic, the number of myocarditis reports has increased in SARS-CoV-2-positive dogs and cats. The link between coronavirus infection and myocarditis is still under investigation. SARS-CoV-2 infections between people and animals are rare, and the ability of animals to spread the virus is not yet considered to be significant.
Myocarditis is usually diagnosed with ultrasonography, as well as possible blood tests. However, myocarditis can only be confirmed via histopathological inspection, which is done post mortem - after the animal has passed. Degeneration of the cells of the myocardium, increased amount of connective tissue, and an inflammatory infiltration - increased number of white blood cells - are visible in the heart biopsy. Because myocarditis mimics the signs and symptoms of many other diseases, diagnosing is often difficult.
The severity and the cause of the inflammation are first examined. If the inflammation has spread widely and the heart has already weakened significantly, the prognosis of the animal is often poor. Usually, an inflammation noticed and treated early on is possible to heal. Myocarditis is most often treated with medication, depending on the cause: bacterial infections are treated with antibiotics, fungal infections are treated with antifungals. Supplements and changes in the animal’s diet may be necessary if nutritional deficiencies are found. If the inflammation is caused by a virus, the animal is monitored and treated with fluid therapy. Pain medication is administered, if necessary. Additionally, patients with myocarditis are prescribed medications that support the heart's function, strengthen the contractions, and ease arrhythmias. The animal is kept at the clinic, under surveillance, until the signs of myocarditis decrease significantly.
Sources:
Animals and COVID-19. (2021). Centers for Disease Control and Prevention. 2021 Nov 18. Available at: https://www.cdc.gov/coronavirus/2019-ncov/daily-life-coping/animals.html.
Chetboul, V., Foulex, P., Kartout, K., Klein, A.M., Sailleau, C., Dumarest, M., Delaplace, M., Gouilh, M.A., Mortier, J., and Le Poder, S. (2021). Frontiers in Veterinary Science. 8:748869. Published online 2021 Oct 21. doi: https://doi.org/10.3389/fvets.2021.748869
Ernandes, M.A., Cantoni, A.M., Armando, F., Corradi, A., Ressel, L., and Tamborini, A. (2019). Feline coronavirus-associated myocarditis in a domestic longhair cat. Journal of Feline Medicine and Surgery Open Reports. Jul-Dec; 5(2): 2055116919879256. Published online 2019 Oct 10. doi: 10.1177/2055116919879256
Janus, I., Noszczyk-Nowak, A., Nowak, M., Cepiel, A., Ciaputa, R., Pasławska, U., Dzięgiel, P., and Jabłońska K. (2014). Myocarditis in dogs: etiology, clinical and histopathological features (11 cases: 2007–2013). Irish Veterinary Journal. 67(1): 28. Published online 2014 Dec 24. doi: 10.1186/s13620-014-0028-8
Kittleson, M.D. (2018). Acquired Heart and Blood Vessel Disorders in Dogs. The Merck veterinary manual. Whitehouse Station, NJ, Merck & Co., Inc.
Lakhdhir, S., Viall, A., Alloway, E., Keene, B., Baumgartner, K., and Ward, J. (2020). Clinical presentation, cardiovascular findings, etiology, and outcome of myocarditis in dogs: 64 cases with presumptive antemortem diagnosis (26 confirmed postmortem) and 137 cases with postmortem diagnosis only (2004–2017). Journal of Veterinary Cardiology. 30, pp. 44-56. Aug 2020. doi: https://doi.org/10.1016/j.jvc.2020.05.003
Rolim, V.M., Casagrande, R.A., Wouters, A.T.B., Driemeier, D., and Pavarini, S.P. (2016). Myocarditis caused by Feline Immunodeficiency Virus in Five Cats with Hypertrophic Cardiomyopathy. Journal of Comparative Pathology. 154(1), pp. 3-8. Jan 2016. doi: https://doi.org/10.1016/j.jcpa.2015.10.180