Assessment Differential diagnoses for Sadie’s cough include feline asthma or allergic bronchitis, bacterial infection, fungal infection, congestive heart failure, lungworms, neoplasia, and heartworm disease. Diagnostic testing A complete blood cell count, serum biochemistry, fecal exam, and thoracic radiographs were performed. The results were as follows: ● Fecal flotation : No parasites seen. ● Complete blood cell count : Eosinophilia (eosinophil count of 2.6, reference range 0.1-0.79), thrombocytopenia (platelet count of 88, reference range 175-600). Based on these abnormalities, a blood smear was reviewed. The blood smear showed adequate platelet numbers with clumping, but confirmed the presence of eosinophilia. ● Serum biochemistry : Within normal limits. ● Thoracic radiographs : On the ventrodorsal view, an enlarged, truncated right caudal pulmonary artery was observed, along with infiltrates surrounding the pulmonary artery. The lateral view revealed mild cardiomegaly with peribronchial infiltrates. Based on the findings above, Sadie was tested for heartworm disease and pulmonary parasites. A heartworm antigen test, heartworm antibody test, and Baermann test (for lungworms) were performed. The results were as follows: ● Heartworm antigen test : Negative. ● Heartworm antibody test : Positive. ● Baermann test (for lungworms) : Negative. Diagnosis Based on the above results, Sadie likely has heartworm- associated respiratory disease (HARD). While a positive heartworm antibody test does not definitively diagnose heartworm disease, a positive antibody test in conjunction with supportive radiographic findings is strongly suggestive of infection with larval heartworms. In addition, Sadie’s Conclusion Many clients (and members of the veterinary team) fall into the trap of thinking that heartworms are only a significant issue in dogs. Unfortunately, recent research has shown that this is not the case. Feline heartworm infections are even more common than feline leukemia and feline immunodeficiency virus infections; heartworms should be discussed and prevented with a similar level of urgency. The clinical signs of feline heartworm disease are varied, leading this syndrome to be underrecognized and underappreciated. Signs in affected cats may range from mild respiratory signs and intermittent vomiting to severe dyspnea and upper respiratory signs. Some cats will remain completely asymptomatic throughout infection, while other cats experience sudden death as their first clinical sign of heartworm disease. Any time that a practitioner sees a cat for suspected feline asthma or other respiratory signs, feline heartworm disease should be on the list of differential diagnoses. A roundtable discussion. Feline heartworm disease: understanding the role of heartworm infection in respiratory disease in cats. (2008). Compendium: Continuing Education for Veterinarians, 30 (8A). Retrieved from https://www.idexx.com/files/feline-heartworm- roundtable.pdf American Heartworm Society. (2016). Bringing the 15th Triennial Heartworm Symposium to you . Retrieved from: https://d3ft8sckhnqim2.cloudfront.net/images/2016_AHS_ SymposiumCB.pdf?1481660692 American Heartworm Society. (2018). Heartworm life cycle . Retrieved from https:// d3ft8sckhnqim2.cloudfront.net/images/pdf/AHS_New_HW_Life_Cycle_VET_CLR_2018. pdf?1534706546 American Heartworm Society, Executive Board of the American Heartworm Society. (2014). Current feline guidelines for the prevention, diagnosis, and management of heartworm (Dirofilaria immitis) infection in cats . Retrieved from https://d3ft8sckhnqim2.cloudfront. net/images/pdf/2014_AHS_Feline_Guidelines.pdf?1461261297 Atkins, C. (2015, June). Feline heartworm disease: basics to breakthroughs . Presented at the ACVIM Forum, Indianapolis, IN. Retrieved from https://www.vin.com/members/cms/ project/defaultadv1.aspx?id=6790522&pid=11719& Atkins, C. E., DeFrancesco, T.C., Coats, J.R., Sidley, J.A., & Keene, B.W. (2000). Heartworm infection in cats: 50 cases (1985-1997). Journal of the American Veterinary Medical Association, 217 (3), 355-358. https://doi.org/10.2460/javma.2000.217.355 References
eosinophilia and lack of heartworm prevention also support a diagnosis of heartworm disease. Treatment Sadie was treated with prednisolone at 5 mg twice daily for three days, then 5 mg once daily for 3 days, then 5 mg every other day until her recheck visit. Additionally, she was started on selamectin for heartworm prevention, in order to prevent the introduction of new heartworm larvae that could further contribute to pulmonary inflammation. Sadie’s owner was also warned that while the medication would hopefully alleviate Sadie’s cough, Sadie would remain at an elevated risk of significant lung complications. Sadie’s owner was instructed to monitor Sadie closely, bringing her to her regular veterinarian or an emergency clinic if respiratory issues were noted. One month later, Sadie returned for a recheck. Her owner reported that her coughing had markedly decreased in frequency, although it had not fully resolved, and she seemed to be doing well at home. Repeat thoracic radiographs were performed. These radiographs revealed a decrease in the pulmonary infiltrates seen one month earlier, though the infiltrates were still visible. Because Sadie’s clinical and radiographic signs had not fully resolved, she was maintained on 5 mg prednisolone every other day indefinitely. Sadie’s owner was given instructions to return every six months for a recheck examination and recheck of thoracic radiographs. Prognosis Over time, most cats with larval heartworm infections will clear the infection. The clinical signs of HARD can often be controlled with prednisolone, though some cats may require long-term or lifelong therapy for permanent changes associated with heartworm disease. It is important to caution owners that some cats with larval heartworms will go on to develop adult worms. If this occurs, adult worms can cause sudden respiratory compromise even in previously asymptomatic cats. While feline heartworm disease can be a challenge to diagnose, combining a number of tests (microfilariae testing, antigen testing, antibody testing, thoracic radiographs, and echocardiography) can increase the likelihood of detecting infection in high-risk cats. Treatment of feline heartworm disease, if diagnosed, presents its own unique challenges. There is no research to suggest an optimal treatment approach. The adulticide that is used in dogs has severe side effects in cats and adult worm extraction is typically impractical in most cases. Therefore, infection is often symptomatic in nature, hoping that the cat will clear the infection before experiencing any severe complications. The prognosis for feline heartworm disease is guarded, and even “recovered” cats will often experience irreversible pulmonary damage. Therefore, the best course of action with feline heartworm disease is to focus on consistent monthly heartworm prevention. Blagburn, B.L., Dillon, A.R., Arther, R.G., Butler, J.M., & Newton, J.C. (2011). Comparative efficacy of four commercially available heartworm preventive products against the MP3 laboratory strain of Dirofilaria immitis . Veterinary Parasitology, 176 (2-3), 189-194. doi: 10.1016/j.vetpar.2010.12.049. Colleran, E. (2017, October). Update on Feline Heartworm and Other Parasites . Presented at Wild West Veterinary Conference, Reno, NV. Retrieved from https://www.vin.com/ members/cms/project/defaultadv1.aspx?id=8216488&pid=19026& European Society of Dirofilariosis and Angiostrongylosis (ESDA). (2017). Guidelines for Clinical Management of Feline Heartworm Diseas e. Retrieved from https://www.esda.vet/ wp-content/uploads/2017/11/GUIDELINES-FOR-CLINICAL-MANAGEMENT-OF-FELINE- HEARTWORM-DISEASE.pdf Guerrero, J., McCall, J.W., Genchi, C., Bazzocchi, C., Kramer, L., Simòn, F., & Martarino, M. (2004). Recent advances in heartworm disease. V eterinary Parasitology, 125 (1-2), 105- 130. Kittleson, M. D., & Kienle, R. D. (2015 revision). Treatment to Kill Adult Heartworms . Small Animal Cardiovascular Medicine, 2nd edition. Retrieved from https://www.vin.com/ members/cms/project/defaultadv1.aspx?id=5496416&pid=5928& Lee, I. T., Levy, J.K., Gorman, S.P., Crawford, P.C., & Slater, M.R. (2002). Prevalence of feline leukemia virus infection and serum antibodies against feline immunodeficiency virus in unowned free-roaming cats. Journal of the American Veterinary Medical Association, 220 (5), 620-2. https://doi.org/10.2460/javma.2002.220.620
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