CHAPTER ONE

INTRODUCTION

1.1       Background of the Study

Toxoplasmosis is a zoonotic parasitic infection caused by Toxoplasma gondii and is

estimated to have infected about a third of the world’s population (Montoya, 2004).

Toxoplasma gondii is a protozoan parasite which belongs to the phylum Apicomplexa,

subclass Coccidiasina and family Sarcocystidae (Hill et al., 2007; Pereira et al., 2010).

This coccidian parasite infects mostly species of warm-blooded animals including man and

birds. There are three (3) strains of Toxoplasma gondii (type I, type II and type III), of

which type I is extremely virulent for mice and type II has been associated with the

majority of toxoplasmosis cases in AIDS patients (Boothroyd and Grigg, 2002; Klaren and

Kijlstra, 2004). Type III is present in animals and has been detected in AIDS patients, but

does not seem to be associated with ocular toxoplasmosis (Boothroyd and Grigg, 2002).

Toxoplasmosis is generally transmitted to humans either congenitally, or via ingestion of

undercooked or raw meat from infected animals, or ingestion of food or water contaminated

with oocysts excreted by infected felids (Montoya, 2004). Ingestion of infected chicken

meat can be a source of infection for Toxoplasma gondii infection in humans and other

animals (Dubey, 2010b). Chickens are considered resistant to clinical toxoplasmosis. There

are only a few reports of clinical toxoplasmosis in chickens worldwide (Dubey, 2008).

There are several reports indicating that both chickens raised in backyard and commercial

free-range systems harbour viable Toxoplasma gondii (Dubey et al., 2004. 2005b).

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Chickens play an important role in the epidemiology of Toxoplasma gondii in the rural

environment, perhaps more than rodents, because they are clinically resistant to

Toxoplasma gondii and     live longer than rodents (Dubey, 2008). Chickens can harbour

mouse-virulent Toxoplasma gondii without showing any clinical signs (Dubey et al., 2002).

Most chickens raised under free range and backyard operations in developing countries are

usually slaughtered at home without supervision. This can allow the transmission of

Toxoplasma gondii infection to humans if care is not taken to wash hands thoroughly after

cutting meat and during cooking of meat. Furthermore, the viscera of such chicken are

usually not properly disposed but left for scavengers thereby encouraging the transmission

of Toxoplasma gondii to reservoirs like rodents or even cats which are the final host

(Ayinmode, 2012). The probability of humans getting infected from ingesting eggs from

infected chicken is not yet substantiated, although Toxoplasma. gondii has been shown to

survived in egg yolk and albumin of boiled egg and yolk of egg fried for 3 minutes, but

there are evidences that showed that raw eggs are not likely to be a source of infection for

humans (Dubey, 2010b). The detection of chronic infection with Toxoplasma gondii in

animals relies primarily on serological assays. There is no gold standard test for the

screening of the large diversity of Toxoplasma host species. The sensitivity and specificity

of the techniques depend on the animal species. Several serological tests have been reported

to be used in the diagnosis of chicken toxoplasmosis, they include Sabin-Feldman dye test,

Indirect fluorescent antibody assay (IFA), Complement fixation test (CFT) and the

Enzyme-linked immunosorbent assay (ELISA) (Hill and Dubey, 2002). Specific enzyme-

linked immunosorbent assays (ELISA) have been developed for some domestic animal

species such as goats and chickens (Dubey, 2011).

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1.2       Statement of Research Problem

There is a high prevalence of toxoplasmosis throughout the world (20%–90%), as well as a

high resistance and persistence of the parasite in a broad spectrum of biological matrixes

(Vaz et al., 2010). Serological studies have indicated incidence of Toxoplasma infections

ranging from less than 1% in young adults in some areas, to 90% among older persons in

other places (Montoya and Remington, 1995). Toxoplasmosis is widespread biologically

and geographically because of its simple mode of contraction. Infection can occur simply

by ingestion of oocysts following the handling of contaminated soil with cat litter or the

consumption of contaminated water or food. However, no direct association has been found

between cat ownership and the risk of toxoplasmosis in people (Walker et al., 2008).

Toxoplasmosis has long been reported to be widespread in West Africa (UNAIDS, 2004).

In sub-Saharan Africa, toxoplasmosis often remains undetected and untreated due to

insufficient diagnostic procedures (Lindstrom et al., 2006). Several studies have shown a

consistently high Toxoplasma gondii seroprevalence for this region, ranging from 35% to

84% in different African countries south of Sahara (Tenter et al., 2000). Considering that

around 30–50% of those coinfected with HIV and Toxoplasma gondii are expected to