1.1 Background of Study
Dirofilaria is a nematode parasite that is widely enzootic in carnivores especially dog. Itis of the family filariidae (Soulsby, 1982). There are two known species of importance in dogs: Dirofilaria repens (D. repens) and Dirofilaria immitis (D. immitis), of which D. immitis is more important and is commonly called the dog heart worm. The adult wormsare found in the right ventricle and pulmonary arteries of dogs and mammals (Gerald and Larry, 1989; Urguhart et al., 2003) and are responsible for delabitating condition known as canine heart worm (CHW) disease or dirofilarosis. Dirofilarosis cause by D. immitis is zoonotic and is transmitted by the mosquito vector (Urguhar et al., 2003).
Heartworms go through several live stages before they become adults to infect the pulmonary artery of the host animal. The worms require the mosquito as an intermediate host in order to complete their life cycle. The rate of development in the mosquito is temperature dependent, requiring approximately two weeks of temperature at above 27oC (80oF). Below a threshold temperature of 14oC, development cannot occur, and the cycle will be halted (Knight, 2000). As a result, transmission is limited to warm months and duration of the transmission season varies geographically. The period between the initial infection when the dog is bitten by a mosquito and the maturation of the worms into adults living in the heart takes six(6) to seven(7) months and its known as the “prepatent period”.
Clinically, the signs of D. immitis infection in dogs are laziness, exercise intolerance, and chronic soft cough with haemophisis. In later stage there are dyspnoe, sometimes edema of the lower limbs and escites, haemoglobnuria, icterus, and collapse of the host usually due to venacaual syndrome (Urguhart et al., 2003).