Prevalence of Dirofilaria Immitis in Dogs

1.0 Introduction
1.1 Background of Study
Dirofilaria is a nematode parasite that is widely enzootic in carnivores especially dog. It is 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 worms are 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 parenchyma disease 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). In Nigeria, (Oduye et al, 2002) stated that heartworms (D. immitis) have been reported in southern Nigeria but not in the northern Nigeria. However, Anyanwu et al. (1996), reported the isolation of D. immitis-like microfilaria in four Nigerian dogs in Zaria. The four cases were mixed infection with D. repens. In a later study, he reported the abundance of mosquito in the study area namely; culex papeins spp. Aedes aegypti and Aedes vitatus (Anyanwu, 2000). Virtually, all these species of mosquitoes are potential vector of D. immitis. In recent past, parasites invasion have been on the increase and constitute a threat to public health.
The increasing association between man and dogs and the recent general insecurity in the country has necessitated the importation of exotic breeds of dogs from Dirofilariasis endemic area particularly to the homes of wealthy Nigerians(Benjamin Edward, 2003). The dog heartworm is of negligible public health risk, because it is unusual for humans to become infected. In addition, human infections are usually of little or no consequences, although rarely, an infected human may show signs of respiratory disease. In most cases, however the heartworm dies shortly after arriving in the human lungs and a nodule known as a granuloma, forms around the dead worm as it is being killed and absorbed. This may well be the most significant medical consequence of human infection by the dog heartworm (Benjamin and Edward, 2003).
The goal of this study is to estimate the prevalence status of Dirofilaria immitis in dogs in Zaria, Kaduna state, Nigeria. Apart from the work done in Southern Nigeria by Oduye and Dipeolu, 2002 and the reported cases of abundances of mosquitoes in Zaria by Anyanwu, 2000 to the best of our knowledge, there is no report on the prevalence of Dirofilaria immitis in Zaria, Kaduna State. As reported by WHO (1995), such a comprehensive study is necessary because it is important to know whether an organism causing disease in a given area is of the biotype as in the local sand fly vectors or in putative animal reservoirs. Furthermore, In developed countries, Dirofilaria immitis infection has long been recognized as a health hazard to dogs and cats and is been controlled vigorously because of its zoonotic significance to human (McCall et al., 2004). According to Idowu (2002), control strategies require information on prevalence, incidence, and health status of the disease. These facts explained the need to undertake this research.

1.2 Statement of the Problem
Since D. immitis was first reported in the South by Oduye and Dipeolu (1976) and the report of suspected cases by Anyanwu et al. (1996; 2000). The disease prevalence especially in dogs has remained poorly researched and reported. Therefore, the extent of the significance of the disease remain unknown in many parts of Nigeria including Zaria.

1.3 Justification
The Dirofilaria immitis of dogs are of public health importance, as their burden can cause much morbidity not only to dogs, but also to human. The finding of this research will therefore, provide useful data to the pool of information needed for effective intervention programmes and subsequent control of the Dirofilaria immitis infection in Zaria and Nigeria generally. It is hoped that the results of this study will further provide reliable data for the determination of the prevalence, and public health significance of the disease towards meaningful planning of appropriate control measures against the disease in the study area and beyond.

1.4 Aim
The aim of this study is to evaluate the prevalence of Dirofilaria immitis infection in dogs in Zaria, Kaduna State.

1.5 Objectives
The major objectives of the study are to:

1. Determine the prevalence of Dirofilaria immitis (heartworm) in dogs in Zaria, Kaduna State.
2. Determine D. Immitis infection in relation to the sex, age and breed in dogs in Zaria.
3. Determine the factors that predisposing dogs to Dirofilaria immitis in Zaria.

1.6 Hypotheses

1. There is no heartworm infection in dogs in Zaria.
2. D.immitis infection is not significantly influenced by the sex, age and the breed of dogs in Zaria.
3. There are no risk factors to heartworm disease in Zaria.

1.7 Limitations of the Study
The variation in the sample sizes across the various sites in Zaria was caused by a number of unforeseen circumstances. Such factors include differences in population sizes of dogs in the sites, denial of access to selected available dogs by dog owners, absence of dogs owners at home at the time of visit, absence of dogs at home at the time of visitation, some dogs are violent, even to the dog owners and to the point that they have to be left aside and lack of time, finance and research logistic problems .The problems could possibly introduce some bias in the sampling but Theis (2005) attributed such bias to non-compensating errors because increasing the size of the sample cannot reduce them.