When Anaemia and Respiratory Distress Point to Canine Heartworm Disease: A Case Study

Canine heartworm disease caused by Dirofilaria immitis can present with nonspecific systemic and respiratory signs, making early recognition clinically important. The disease is distributed worldwide and is more common in tropical and subtropical climates where temperature and humidity favor both the nematode and its mosquito vectors^1,2. In Nepal, its presence has been documented, highlighting the need to consider dirofilariasis when dogs present with unexplained weakness, respiratory abnormalities, anaemia, or other compatible clinical findings. 

A four-year-old male Japanese Spitz weighing 5.5 kg was presented with anorexia, vomiting, diarrhoea, weakness, reluctance to move, respiratory difficulty, and abdominal discomfort. The history indicated that symptomatic treatment for anaemia, lethargy, and anorexia had already been provided for several months³. 

Clinical Presentation and Initial Assessment³ 

On examination, the dog's temperature was 101.7°F. Respiratory rate was moderately increased at 44/min, while heart rate was 138/min. Pale mucous membranes and dehydration were evident, with a capillary refill time of 2 seconds. Peripheral lymph nodes were within normal limits. 

The combination of chronic nonspecific illness, respiratory difficulty, marked weakness, and pale mucous membranes warranted further investigation rather than continued symptomatic management alone. 

Two blood samples were collected in EDTA vials from the radial vein. Haematological analysis demonstrated severe abnormalities: 

• Haemoglobin: 3 g/dl 

• Platelets: 140,000/mm³ 

• Total WBC count: 3,750/mm³ 

• Neutrophils: 3,260/mm³ 

• Lymphocytes: 300/mm³ 

• Monocytes: 95/mm³ 

• Eosinophils: 95/mm³ 

• Basophils: 0/mm³ 

These findings indicated severe anaemia accompanied by thrombocytopenia, leukopenia, lymphocytopenia, monocytopenia, and eosinopenia. 

Diagnostic Finding³ 

A peripheral blood smear provided the critical diagnostic clue. One drop of peripheral blood was placed on a clean glass slide and examined under a compound microscope using a 40X objective. Undulating movement of larvae consistent with Dirofilaria immitis was observed. 

Based on the clinical history, physical findings, haematological profile, and detection of D. immitis larvae in peripheral blood, the case was diagnosed as dirofilariasis. 

For practitioners, this case demonstrates the value of direct microscopic examination when heartworm infection is clinically suspected. The disease may remain chronic and asymptomatic during its earlier development, and dogs carrying circulating microfilariae can contribute to infection of local mosquito populations. 

Supportive Management and Outcome³ 

Because the dog was dehydrated and anorectic, supportive management was initiated. It received 400 ml of normal saline, including 300 ml intravenously and 100 ml subcutaneously, along with 200 ml of dextrose saline. Pantoprazole and ondansetron were administered intravenously, while an oral haematinic preparation containing iron, vitamin B12, folic acid, zinc, and L-lysine was given at 5 ml twice daily. 

Despite these measures, the dog was found dead the following day. The post-mortem examination was not performed because the owner was unwilling. 

Practical Clinical Insights 

The marked anaemia may have been associated with trauma caused by parasite movement affecting red blood cells and vascular walls. Thrombocytopenia may be associated with immune-mediated platelet destruction or increased thrombocyte activity during heartworm infection. Respiratory abnormalities may occur in association with pulmonary vascular and inflammatory changes. 

The case reinforces the importance of including D. immitis among differential diagnoses in dogs with compatible clinical signs, particularly in areas where mosquito exposure and environmental conditions may support transmission. Early consideration of the disease, appropriate screening, and strategic vector control may help reduce its clinical and epidemiological impact. 

References 

1. Taweethavonsawat P, Rattanapinyopituk K, Tachampa K, Kiertkrittikhoon S, Jitsamai W, Klomkleaw W, Choisunirachon N, Komin K. Case report: Thromboembolic heartworm induced lower limb necrosis in a dog. Frontiers in Veterinary Science. 2022 Aug 3;9:868115. https://www.frontiersin.org/journals/veterinary-science/articles/10.3389/fvets.2022.868115/pdf 

2. Rimal S, Adhikari A, Acharya R, Singh DK, Joshi NP, Shrestha B, Kaphle K, El-Dakhly KM, Giannelli A. Occurrence of Dirofilaria immitis in stray dogs from Nepal. Acta Parasitologica. 2021 Dec;66(4):1222-8. https://www.researchgate.net/profile/Khaled-El-Dakhly/publication/351024610 

3. Pandey K, Paudel S. A Case Study on Canine Heartworm (Dirofilaria immitis). NPI Journal of Science and Technology. 2024 Aug 20:115-21. https://nepjol.info/index.php/npijst/article/download/68947/52685