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).
Canine heartworm infection can be diagnosed based on the clinical signs of cardiovascular dysfunction; demonstration of microfilaria in the blood; thoracic radiography showing thickening pulmonary artery and/ or a positive enzyme linked immunosurbent Assay (E.L.I.S.A) immunochromatography test system. At postmortem, presence of worms in the right ventricle and pulmonary artery are diagnostic.
Dirofilariasis manifests either as subcutaneous nodules or asymptomatic parenchymadisease in human. These lesions are often misdiagnosed as malignant tumors, requiring invasive investigation and surgery (Bionote, 2010).
Heartworm has now spread to nearly all locations where the mosquito vector is found. Transmission of the parasite occurs in all of the United States (cases has been reported in Alaska and the warmer regions of Canada). The highest infection rates are found within 150 miles of the coast from Texas to New Jersey, and along the Mississippi river and its major tributaries. It has also been found in South America, Southern Europe, Southern Asia, The Middle East, Australia, Korea and Japan. ( Edward, 2003).
PREVALENCE OF DIROFILARIA IMMITIS IN DOGS IN ZARIA