Heartworm Disease

Chapter 10 Heartworm Disease



Clay A. Calvert, Justin David Thomason




HEARTWORM DISEASE



Etiology and Life Cycle


Heartworm infection is produced by the parasite Dirofilaria immitis and is transmitted to dogs mostly by 10 to 15 species of mosquitoes. Mosquitoes can transmit infective larvae (L3) 2 to 3 weeks after ingesting a blood meal. Infection rates vary among cats in endemic regions but are usually 10% to 20% of that of dogs within the same enzootic region. Being male, a large breed, and outdoors increases the risk of infection in dogs.



Canine Infection Life Cycle

















Pathogenesis


Disease onset and severity largely reflect the number of adult heartworms. In infected cats, the average number of adult worms is 3 to 6, depending on the concentration of infected mosquitoes and the ambient temperature in any given region.








Clinical Signs


The clinical signs associated with heartworm infection reflect the adult worm burden, duration of infection, and host-parasite interaction. Respiratory signs are most prominent.




Cats






Diagnosis


The diagnosis of heartworm infection in dogs is based on immunodiagnostic antigen testing. Microfilaria in the peripheral blood can be detected by a direct smear or a concentration test (modified Knott test or millipore filter test) in dogs with or without clinical or radiographic findings consistent with the disease. Testing puppies younger than 6 months of age is not indicated.


Affected cats usually lack circulating microfilaria, may have suggestive radiographic abnormalities, and echocardiography is very useful. A positive enzyme-linked immunosorbent assay (ELISA) test for heartworm antigen, antibody or both may be present.




Clinical Pathology


No abnormal test results are pathognomonic for heartworm infection.





Aug 15, 2016 | Posted by in SMALL ANIMAL | Comments Off on Heartworm Disease

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