ABSTRACT
Dog heartworm. Transmitted by mosquitoes. PPP= 7 months. Dx: Microfilariae in blood or by antigen detection test. Antigen tests on rare occasions negative in dogs with adult worms and high microfilarial counts, but usually correspond very well to tests for microfilariae. Habitat: Pulmonary arteries and right heart. Similar Species: Microfilariae (300 µm long) can be confused with those of Dipetalonema reconditum. Dirofilaria immitis microfilariae are wider at midbody than RBCs and the head tapers gradually to tip. Range: World, wherever dogs and mosquitoes are prevalent and temperatures are warm enough to support growth within the mosquito vector. Clinical Signs: Usually respiratory signs of cough, tachypnea, exercise intolerance, syncope, rarely hemoptysis. Usually divided into 3 classes: Class I-asymptomatic, no radiographic signs or anemia; Class II-cough, exercise intolerance, anemia (between 20 and 30%), radiographic signs pulmonary artery enlargement; Class III-cardiac cachexia, severe cough at rest, signs of right heart failure (ascites), severe radiographic signs RSHF, enlarged pulmonary arteries, lung infiltrates from thromboembolism and severe anemia (<20%). Potential Zoonosis: Rare lung nodules in humans who have been infected by bite of mosquito. Tx: Immiticide® (melarsomine dihydrochloride; Class I and II: 2.5 mg/kg, IM deep in lumbar muscle, q24h for 2 doses repeated 4 to 6 months later if antigen test still positive. Class III: stabilize heart failure first with aspirin, glucocorticoids, furosemide, use 2.5 mg/kg, IM deep in lumbar muscle, once, then in 1 month, give 2.5 mg/kg, IM deep in lumbar muscle, q24h for 2 doses).
