The overall prevalence of T. gondii antibodies in the slaughtered animals was found 56.2% (95% CI: 52-67.3). This is relatively compatible with the previous findings in Southwestern Ethiopia (35). In contrast, it is higher than several reports from different regions of Ethiopia (16, 18, 19, 36, 37). These variations between reports might be ascribable to the presence of stray cats; intermediate host susceptibility, and the nature of infectivity of T. gondii in different agro-ecological areas; local climate variation of the country, and the types of serological test used and their cut-off values. In this study, the sample size might not estimate the seroprevalence rather confirm the existence of this infection in these study animals (3, 38, 39). Furthermore, the current finding might also be influenced by the site of a collection of blood samples at the slaughter line and cardiac blood of butchered animals, which are present with other non-specific inhibitors, leads to lower the specific concentration, and non-specifically binding of anti-T. gondii antibodies (9).
Species wise prevalence of T. gondii infection was found 62% in sheep, 52.7% in goats and 54.7% in cattle. These findings were not varied between species to species. However, sheep were more exposed for T. gondii than cattle and goats. This coincides with the findings of Gebremedhin et al. (36), Lahmar et al. (40), Sharma et al. (14), Ethicha et al. (16), Getachew et al. (11), Rasti et al. (11) and Bentum et al. (41). These might be referred to the feeding behavior of sheep were grazing on the ground than goats which browse shrubs, and cattle are less susceptible to this parasite (3, 42). Nevertheless, it’s also contradicted by the reports of Ayinomode and Abiola (43) in Nigeria who speculated that cattle were more exposed for this parasite than sheep and goats, and Ahmed et al. (44) in Pakistan also said that the goats were more exposed for T. gondii than sheep due to the management practice of semi-housed goats were highly experienced for grazing and browsing of feed. According to these authors, these fluctuations might be also ascribable to the susceptibility of the hosts, and the virulence and strain type of T. gondii (2, 38, 45).
These current seroprevalence of T. gondii in sheep (62%) and goats (52.7%) were too altered from other previous stories, concurs within Ethiopia (16, 35); Egypt (11, 46); South Africa (41) and India (14). However, these present findings are also higher than the previous reports from different areas of Ethiopia(17–19, 36, 47, 48); Nigeria (43); Ghana (12); Tunisia (40); China (49, 50) and Iran (51). Along the other hands, these findings are also lower than Hussain and Zahid (41) who reported as 86.4% in sheep, 81.8% in goats and 72% of cows in Pakistan. In the case of cattle, the present anti-Toxoplasma antibodies detection (60%) is also higher than the previous reports of 25%(18) and 10.7% (19) from different parts of Ethiopia. These variations of the present findings and the previous above-mentioned studies hypothesized to the varied geographical regions; host factors, husbandry practice; the poor hygienic conditions of feed and water; the presence of domestic cats; types of diagnostic test used, and their cut-off value and sample size. Moreover, the disease has more occurred in warm and moist areas than cold or hot areas to sustain the existence of viable sporulated oocysts in the moist environment(1, 4, 38).
The univariate logistic regression analysis of T. gondii in slaughtered animals showed that female sheep and goats were 3 and 4 times more likely exposed to this parasite than male sheep(COR = 3.030; P = 0.016) and male goats (COR = 4.459; P = 0.001), respectively. This significant female sheep finding corresponds with the previous studies from the globe (11, 41, 43). It was also contradicts from the world (14, 16, 19, 35, 49). In case of goat sex finding was also parallel to the previous reports from Ethiopia (16, 19, 35, 52) and else in the globe (12, 41, 50). Whereas, previous reports from Ethiopia (18, 47) contradicted these findings in which males were more exposed than female goats. These reports might be speculated as female sheep and goats are more exposed by T. gondii than their males due to the immunocompromised of breeding female animals during the stress of lactation and pregnancy leads to more acquiring T. gondii infection than males. Moreover, these female animals are too exhibited by males through contaminated semen during ejaculations which are also congenitally transmitting this parasite through tachyzoites for future generations(53). However, in the event of the stress of male animals due to the marketing purpose and stimulate of its androgen hormones are decreases the immune status of male animals, which leads to more peril by this parasite than female sheep and goats (45).
Likewise, this logistic regression analysis also demonstrated that adult sheep were 5 times more exposed to this infection than the young sheep (COR = 4.114; P = 0.006). This corresponds with the previous reports from Ethiopia (16, 18, 35, 36, 54) and else in the globe (13, 40, 41, 49). But, it contradicted by Getachew et al.(18)from Ethiopia. Whereas, adult goats were 0.7 times less acquired this parasite than young goats (COR = 0.308; P = 0.008). This finding contradicts within the various reports from Ethiopia (16, 35, 52). This increasing infection rate in the adult group of slaughtered animals might be attributed to cumulative exposure of animals for long-lived acquiring oocysts from the environments, and the presence of stray cats during grazing in the land, and long journey transport of animals for marketing purpose might be predispose the animals for this parasite (1, 54).
The logistic regression analysis showed that Wogera origin of goats were 2.5 times more acquired T. gondii infection than the Gonadr-zuriya originated goats. This finding coincides with the earlier reports (35, 36). However, it contradicts the reports of Getachew et al. (18). These might be the climatic difference of Wogera is moist and humid than Gondar-zuriya districts which is suitable for survival of oocysts of T. gondii (3). In case of breeds of cattle, cross breeds were 4.5 more exposed to this parasite than the local breeds. This constituent with the results of Geberemedhn et al.(36) and contradicts the reports of Tilahun et al. (11). Breed difference in T. gondii seropositivity was unknown. However, these might be ascribed to the cross breeds are native to the natural area and less resistance for T. gondii infection than the local breeds.
The overall first PCR and nested PCR T. gondii DNA findings were found in 21.2% (95% CI: 16–34) and 10.6% (95% CI: 6.7–16) in slaughtered animals, respectively. These findings were lower than the present serological findings of 56.2% of slaughtered animals. These might be attributed to the molecular assay is the best sensitive and specific tests of any stages of this disease in the hosts. Whereas the serological tests lack sensitivity and specificity and it depends on the anti-Toxoplasma antibodies production following the infected hosts (24). Moreover, the synergistic effect of the serological and molecular tests has more importance to confirm the presence of this parasite in biological samples (23). This also ascribed to the consumption of one cyst containing hundreds of bradyzoites is enough for a cat to be invaded which might also be acquiring this infection to their intermediate hosts (3, 4).
Moreover, there were fair correlation between LAT with first PCR findings (Kappa: 0.230) and first PCR and nested PCR findings (Kappa: 0.101), and slight agreement between LAT with nested PCR results (Kappa: 0.338) among slaughtered animals. These also attribute to the nested PCR technique is more sensitive and specific copies of the long DNA segments by applying two sets of primers than the conventional PCR, which are applied in two successive PCR within generating DNA products that have intended target site and non-specifically amplified DNA fragments in the first reaction rather than the second reaction (8, 24). These concordance results are influenced by the presence of false-positive results due to cross contamination. It is not totally removed risks in this best sensitive test of nested PCR for the diagnosis of T. gondii in practical investigations even if too performed at controlled areas (23). Moreover, nested PCR also takes more detailed knowledge of the target sequence of this disease(8).
These present overall first (22.7%) and nested PCR (11.3%) findings among slaughtered ruminants are also parallel to the former molecular reports of 9.47% using nested PCR in Southern Ghana (55). These findings also higher than 15.52% in Bangladesh (56); 13.33% in central Iran (51); 14.3% from ovine aborted fetus and stillborn in Brazil (57); 17.33% in Northwestern Iran (58) and 7.38% in Egypt (11) who were reported the positive T. gondii DNA by using PCR assays, and 1.5% using nested PCR in North India (33). However, these current findings are also lower than the earlier nested PCR reports of 53.13% of bioassayed mice in central Ethiopia (23) and 31.25% in Southern India (59). These might be ascribable to the various types of PCR and its targeting gene of T. gondii; the climate variation; the susceptibility of host and their parasite virulence. Moreover, the lower molecular detection of this parasite attributes to using a minuscule quantity of minced tissues that were unevenly distributed of this parasite in the entire affected tissue(25). The specimen’s type and its collected timing, which are indicated with this parasite is more harbors in tissue than blood for a long time, and is more advantageous to get a positive finding of T. gondii DNA in tissue than blood samples in whatever stage of infection (1).
In the case of species wise molecular results, 34%, 21.8%, and 9.1% by first PCR of T. gondii DNA targeting at B1 gene were positive in sheep, goats and cattle, respectively. These agree with the previous reports of 33.3%, 32.5% and 19.3% in sheep, goats and cattle, respectively (60), and 28% sheep and 16% goats (58). Nevertheless, these results were also more eminent the reports of 1.69% sheep and 1.34% goats (33); and 17.8% sheep and 8.9% goats (51). In the case of nested PCR findings of these species, 20%, 12.7% and 0% of T. gondii DNA targeting at B1 gene were also positive in sheep, goats and cattle, respectively. These findings were consistent with the previous reports of 9.84% sheep and 10.73% goats (61). It were too lower than 53.13% in both sheep and goats (23); 52.7% sheep and 41.7% goats (46), and 29.09% sheep and 38.23% goats (59). These the current first PCR and nested PCR, and the aforementioned various reports of molecular detection of this parasite might be supposed to the sampling size, quantity and type of minced tissue, bioassay mice virulence, agro-ecological area and climate change, the presence of felines, the types of PCR used and its targeting gene type, the susceptibility of slaughtered animals; primer design and PCR optimization protocols and the types DNA extraction kits manufacturer (1, 8, 25). Moreover, detection of T. gondii in heart tissue is mainly the preferable and a suitable predilection study site than another entire almost all edible animal tissues during the same stage of infection that remain viable of cysts for a long time in food animals(4, 59).