Prevalence Of Dirofilaria Immitis In Dogs

Project and Seminar Material for Biology

Prevalence Of Dirofilaria Immitis In Dogs


The study on prevalence of Dirofilaria immitis was conducted in Zaria. A total of three hundred and seventeen dogs were examined from seven sampling sites; Samaru, Sabon Gari, Tudun Wada, Wusasa, Basawa, Kongo and Gyellesu from April to December 2012. 5mls of blood from the branchiocephalic vein was aseptically collected from each dog and was stored in sample bottle containing ethylene diamine tetra acetic acid (EDTA, 1mg/ml) and were transported to the laboratory in a cold box and analyze immediately on arrival, using modified knotts method.

The overall prevalence of confirmed cases of Dirofilaria immitis infection in the dog population in Zaria was (48) 15.1%. Age specific prevalence showed that, infection was detected throughout the age 1 – 2 years old to 9 years above. Although the 1 – 2 years showed a high rate of infection in 66 dogs (21.2%) than the other ages respectively. The male dogs were relatively more infected than the females, 40 (81.9%) and 8 (8.3%) respectively. The disease was detected in all the sites.

The foreign breeds were found to be free from the infection, these is probably due to the fact that special care are given to them. Prevalence was higher in un-caged and caged dogs. 34 (15.2%) and 14 (14.9%) respectively. There was not significant difference (p>0.05) in prevalence. A higher percentage of the positive cases showed low haemoglobin level 8 (21.6%), The reason could be that the infection causes anemia which in turn affects the level of hemoglobin likewise the total protein count 16 (13.2%). WBC count increased in positive cases which is indicative of Dirofilaria infection while the RBC is low in positive cases 7(14.8%).

These indicates that the presence of the parasite does not affect the RBC. It not significant (p > 0.05) in blood counts. Differential count of the WBC showed that the presence of the infection led to the release of a greater number of white blood cells such as Eosinophils, Lymphocytes, Monocytes and Neutrophils. Analysis of the blood parameters showed positive correlation between the packed cell volume and haemoglobin, packed cell volume and red blood cell, haemoglobin and red blood cells, while the Neutrophil and lymphocytes showed negative correlation. The result of the study shows that Dirofilaria immitis infection is prevalent among dogs in Zaria, and indicates that D. immitis infection may be of public health concern then wither to envisaged.

Chapter One


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 Research Proble

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 Limitation 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.

Chapter Five

Summary, Conclusion and Recommendation

5.1 Summary

A total of 317 dogs were examined, the prevalence of 15.1% were confirmed cases of Dirofilaria immitis in Zaria. 1 – 2 years old dogs has the highest infection rate. The male dogs shows high rate of infection based on sex. Dogs uncaged are highly infected.

Infection was recorded in all site/location in Zaria.

The age, sex, breed, home, location, packed cell volume, Neutrophil, Monocyte and Eosinophil showed no significant differences (P>0.05).

Furthermore, when white blood cell, lymphocytes, total protein count and haemoglobin concentration in the dogs are low it shows high rate of infection and shows highly significant difference (P<0.01) while the red blood cell shows a significant difference (<0.05).

The packed cell volume and haemoglobin, packed cell volume and red blood cell shows positive correlation while Neutrophil and lymphocytes showed negative correlation.

The presence of potential vectors (mosquitoes) Culex papiens, Aedes aegypti and Aedes vitatus of Dirofilaria immitis in Zaria, and a favorable climates that aids its vast breeding coupled with the wandering habit of the dogs (male), exposing it to a mosquito bite which aids the fast spread of Dirofilaria immitis in Zaria.

The presence of the vector (mosquito) in Zaria aid the spread of Dirofilaria immitis in dogs in Zaria.

5.2 Conclusion

  1. The prevalence rate of 15.1% was found in Zaria from a population of 317 dogs.
  2. The prevalence of Dirofilaria immitis was higher in male than in female, higher in 1-2 years age group than the other age group and higher in local breeds than exotic and mixed breeds.
  3. Uncaged dogs showed more positive cases of the Dirofilaria infection than caged/restricted dogs.

5.3 Recommendations

It is therefore recommended that preventive measures have to be taken in order to reduce the high infection rate of the disease in our local pets – the dogs. Such measures include;

  1. Control through screening of dogs and therapeutic intervention.
  2. Proper enlightenment and education about the disease through health education.
  3. People should be encouraged to take their dogs to veterinary clinics for routine examination and possible treatment.
  4. Control of known vectors is necessary
  5. Early treatment of human cases if detected.

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