Toxoplasma gondii, an obligate intracellular protozoan parasite, is a common intestinal coccidian of the cat. Infected cats shed oocysts in feces and contaminating environment (Etinger, 1983; Jackson, 1989; Soulsby, 1996).
Animals like carnivores and herbivores ingest oocysts and become infected. T. gondii encysts in intermediate hosts, cysts can be found in the CNS and muscles of intermediate hosts. Indeed, the zoites of parasite can transfer via placenta and cause abortions and stillbirth in sheep (Levine, 1985; Robert, 1991).
In humans, infection with T. gondii may be acquired or congenital, infection is generally acquired from consuming insufficiently cooked meat containing cysts, or by ingesting sporulated oocysts in food, water, or from contaminated environment.
T. gondii infection is one of the most widespread parasitic infections among humans throughout the world. Approximately 30% or more of adult human populations in the world have serum antibodies against T. gondii (Dubey and Battic, 1988, Ghorbani, 1981).
Public health concerns associated with T. gondii clearly indicate the need for epidemiological investigation of toxoplasmosis. This study was conducted to determine the seroprevalence of antibodies to T. gondii in populations of sheep in Chaharmahal and Bakhtiari in the center of Iran.
MATERIALS AND METHODS
Sample collection: One thousands blood samples were collected from the populations of sheep (Female 600 and Male 400) of five counties of the province (200 for each of them) in the first of summer (2002), by cluster random sampling method.
All the blood samples were collected in serum separator tubes and then centrifuged at 1200x for 10 min. Serum samples were decanted into storage tubes and stored at -30°C until analysis.
Serological examination: All sera from sheep were assayed for antibodies against T. gondii by using of Indirect Fluorescent Antibody Test (IFAT). T. gondii antigen was prepared by Pasture Institute of Iran, from tachizoit of parasite that killed by formaldehyde 10%. Conjugated serum with Fluorescein Isothiocyanate prepared by Razi Institute of Iran.
After screening the serum samples with dilution of 1:20, for titration of positive
serum, dilution of 1:40, 1:80, 1:160, 1:320 were prepared from serums and examined
by the same method. The last titer with positive fluorescent reaction was chosen
as titer of serum samples.
A titer more than 1:20 was considered as positive for serum antibodies to T. gondii in sheep.
Statistical analyses: A titer more than 1:20 was considered as positive for serum antibodies to T. gondii. Seroprevalence was defined as the percentage of positive samples for antibodies to T. gondii.
The Chi-Square statistical test (χ2) was used to determine the difference among different counties and between sexes. A value of p<0.05 was considered significant.
RESULTS AND DISCUSSION
Serum samples from 1000 sheep were collected and checked for antibodies to T. gondii by IFAT method. The total population of sheep with serum antibodies to T. gondii in the Chaharmahal province was 29.1% (291/1000) (Table 1).
The seroprevalence rate in 5 counties: Shahrekord 38% (76/200), Borujen 22.5% (45/200), Lordegan 18% (36/200), Farsan 32% (64/200) and Ardal 35% (70/200) (Table 1).
The results showed a significant difference (p<0.05), between the counties located in east (Borujen and Lordegan) and west (Shahrekord, Farsan and Ardal) parts of the province, but no significant difference was observed among counties in each of those area.
The number of seropositive sheep did not differ between male (27.8%, 111/400) and female (30%, 180/600), (Table 2).
The titration of positive samples were with the following titers: 11% with 1/20, 9.3% with 1/40, 15.1% with 1/80, 28.9% with/160 and 35.7% with/320 or more (Table 3).
||Seroprevalence of antibodies to T. gondii in sheep
in Chaharmahal and Bakhtiari-Iran
|a, b, numbers with different superscript in the some column
differ significantly, (p<0.05)
||Seroprevalence of antibodies to T. gondii in sheep
between tow sex in Chaharmahal and Bakhtiary-Iran
||Serum titration of seropositive sheep to T. gondii in
Chaharmahal and Bakhtiari-Iran
Seroprevalence of antibodies to T. gondii in sheep varies depending on the age of sheep, method of serology testing and geographic location. Infection with T. gondii is common in sheep, based on reports involving a total of 9654 animals (Fayer, 1981) calculated that the average world wide prevalence of anti Toxoplasma antibodies in sheep was 31% with the range of 0 to 96%.
Blewett and Watson (1983) reported that 33% of sheep in the UK have experienced infection with Toxoplasma. Indeed, world wide serologic findings have been shown that, more than 30% of human populations have serum antibodies to T. gondii. Several investigators (Claus et al ., 1977; Dubey and Beattie, 1988, Dubey et al., 1995; Monica et al., 2002) have determined the seroprevalence of antibodies to T. gondii in feline (39-68%) and rodents (0.8-6.3%).
A number of investigators (Dubey et al., 1995; Gamble et al., 1999; Weigel and Dubey, 1995) have shown that farm animals in close contact with cats and rodents have a higher exposure risk to T. gondii.
Regarding to the results of this study, a titer of 1:20 was considered as infection of T. gondii in sheep, the seroprevalence rate of antibodies to T. gondii was 29.1% in the Chaharmahal and Bakhtiari. The lower seroprevalence rate observed among sheep in the east part of the province might be attributed to the climatic properties and the method of husbandry of sheep in these area. In the west and south parts of the province sheep were migrated to the other province (Khozestan) during autumn and winter which substantially had a higher humidity condition and it could be a cause of higher titer to T. gondii among sheep in the west and south parts of the province.
Furthermore, the results of this study showed that, there was no significant difference between sexes for antibodies to T. gondii. Aristeu et al. (2003) in Brazil showed that, the prevalence of antitoxoplasma antibodies in the sheep and goat were 35.3 and 40.4%, respectively. In contrast to the current study a significant difference between sexes in goat and sheep was found.
As the results show, about 89% of positive serum samples showed titer more than 1:20. It may indicate an active infection which can cause not only abortion and congenital problems in pregnant sheep but also in human who are in close contact with infected sheep or consumer who use the milk or meat of affected ones.
The results of our study and other investigators have shown that the prevalence of antibodies to T. gondii in sheep is high, for fulfillment the findings, it is necessary to conduct a study for assessment the rate of abortion caused by this parasite in sheep.