Toxoplasmosis caused by an obligate intracellular protozoan parasite, Toxoplasma gondii, is a widely distributed infection that affects humans, pets and livestock in both developing and developed countries including Ghana . However, in Ghana studies that have been conducted are mainly in the southern part of the country. This has necessitated the current study in the middle belt of Ghana.
The seroprevalences of 78.1% and 75.0% recorded among the pregnant women from the Asunafo North District in the Ahafo and the Bosomtwe District from the Ashanti Region respectively are high compared to 30%–65% reported as the global population infection status by Ayeh-Kumi in 2010 . However, it was lower when compared to previously recorded seroprevalence of 92.5 % in the Greater Accra Region of Ghana by Ayi et. al., in 2009 .
The transmission and the subsequent seropositivity to the parasite is reported to be relatively higher in hot and humid areas such as Africa and as such prevalences are higher in some parts of the world as compared to others [23–24]. This is because the longevity of the viability of the T. gondii oocysts are enhanced in hot and humid conditions. In Brazil, approximately one in two people have the infection (51%) and this shows a high seropositivity . On the contrary, a moderately low prevalence of 18.9% was recorded for Finland, 28% for Denmark and 39% for the United States where the temperature and humidity is relatively low. It is therefore not surprising that Ghana, a tropical country with hot and humid climatic conditions, has high seroprevalence as reported in this study for the two Districts and other studies [5, 18, 21].
There was no association (P>0.05) between seroprevalence and the various risk factors as well as demographic properties assessed in this study in both Districts. Thus, the study supported previous and recent epidemiological studies which showed that cat ownership and other risk factors of the T. gondii infection were less predictive in determining the acquisition of theinfection . It has been reported that one does not necessarily have to come into contact with cat or its faeces to acquire the infection, but rather a higher risk for toxoplasmosisinfection is generally imposed on human communities with high exposure to cats, its faeces and/or the extensive art of lambing since free oocysts will constantly be circulating in the environment . Nevertheless, the high seroprevalences reported in this study could be due to other notable risk factors such as the carrying of oocysts from faecal matter to food by flies and the drinking of contaminated water as observed in some outbreaks [27–29]. In an environment such as where the studies were conducted, one does not have to own a cat to get the infection since cat faeces are all over the environment.
Seropositivity and antibody concentration were found to increase with age until after 30 years where there was a decline. This is because as one ages, he becomes increasingly exposed to the infection as has also been reported in other studies, that the rate of the infection acquisition increased by 0.5% to 1.0% per year of age, with the total prevalent antibody level gradually increasing with age, reaching a peak of 23.7% in the active life years [30–32].
Even though higher number of participants from Asunafo North District had previously been exposed compared with Bosomtwe District, the number of ongoing infections were not different. Probably because the two districts have the similar climatic conditions even though Ghana Statistical Service in their 2010 Population and Housing Census reported that the average humid and temperature conditions in Ahafo Region is higher than that of the Ashanti Region .
The study also showed that there were significant differences (P<0.001) in the seropositivity of anti- T. gondii IgGs relative to their respective anti-T. gondii IgMs in both Districts (Table 2). This showed that a high proportion of these pregnant women (99/146 in Asunafo North, 72/120 in Bosomtwe) have had previous or past exposures compared to those with recent exposures (34/146 in Asunafo North, 36/120 in Bosomtwe). The tendency of this past infection being in latency with persisting tissue cysts (bradyzoites) especially those who were seropositive for both IgG and IgM poses a high risk to the foetuses of these pregnant women since vertical transmission of the infection can occur if the mother acquires an acute infection duringpregnancy. However, an acute infection may result from either a primary (recent) infection or re-activation/re-occurrence oflatent (chronic) infection in any case of immuno-suppression. Since latency can be established in the nerve ganglia of the brain, eye and the striated muscles of the heart (tissue tropisms varies in persons) and resurface later when the immuno-competent person becomes immuno-suppressed later in life, the development of the foetuses are then at risk [5, 34–35].
From this study, all the IgG seropositive pregnant women could probably have their foetuses contract congenital toxoplasmosis in case of parasitic re-activation from the nerve ganglia of the tropic tissue where chronic stage Toxoplasma gondii tissue cysts (bradyzoites) will be released into the blood stream and be transformed into tachyzoites, which is the acute stage T. gondii tissue cysts to cause the infection.
It has been reported in other studies that an acute maternal infection in the first trimester of the human gestation period results in a foetal transmission rate of 10–15%, rising to about 68% in the third trimester of the gestation period [14–16, 36]. In this study, the total number of IgG and IgM seropositivity increased from the first trimester to the third trimester (Table 2). Although, there was no statistical difference (P>0.05) in the mean antibody concentration levels from trimesters one to three (Figure 1B), the babies that would be born to the anti-T. gondii IgM seropositive pregnant women are at a greater risk of contracting congenital toxoplasmosis, especially those in their first trimester. This is because the IgM seropositive pregnant women would have carried the acute infection together with the foetus in the uterus for at last 6 months before delivery and that prolongs the time span for probable foetal contraction of the infection [7, 11]. What is not clear is whether this high seroprevalence observed would translate into clinical manifestations or not in the new borne babies. There is therefore the need for a follow up study to follow the babies to assess whether they will exhibit any clinical manifestation of the infection.
In 2008, Afonso et al., in their study that assessed the spatial distribution of soil contamination by T. gondii in relation to cat defaecation behaviour in urban areas reported that the extensive lambing and the improper keeping of cats as pets without sand boxes continually contaminate the soil. It was also established that the risk of infection was not related to the owning of a cat but rather being exposed to the faeces of a cat with shed oocysts .
Contrary to Dubey’s (2004) and Afonso’s (2008) studies [8, 37], all the risk factors analysed in this study showed no correlation and significance (OR<1) with the T. gondii infection status of the participating pregnant women. The difference between the T. gondii seropositive pregnant mothers who had been exposed to the risk factors assessed and that of the mothers unexposed in this study was statistically not significant (P>0.05).
This study supported previous and recent epidemiological studies which showed that cat ownership, a high risk factor for T. gondii infection, was less predictive in the acquisition of the T. gondii infection . Thus, it can be deduced that one may not necessarily have to come into contact with cat or its faeces to be infected, rather a high risk for toxoplasmosis infection is imposed on human communities with high exposure to cats and/or the extensive lambing since free oocysts will constantly be circulating in the environment .
Meat and vegetable consumption as well as general eating habits have also been widely reported as risk factors for T. gondii infection . In Ghana and other countries, it has been reported that the infection is found in most farm animals especially in pigs, sheep and goats and thus their ingestion could lead to the infection [39–40]. However in this study, no relationship was found between meat and vegetable consumption and T. gondii infection.