Seroprevalence of Brucella Antibodies in Household Goats in Benue North-East Senatorial District, Nigeria

MATERIALS AND METHODS

Study location: A cross-sectional study was carried out in the North-East region of Benue State, Nigeria (Longitude 7°47΄ and 10°0΄E; Latitude 6°25΄ and 8°8΄N) between April and June, 2013. Benue State lies in the Middle-Belt region of Nigeria within the Guinea savannah zone. It has a typical tropical climate with two distinct seasons, the rainy and the dry season. Agriculture is the mainstay of the state’s economy, food security and support for livelihood of the rural people. Livestock produced in the state are majorly goats, sheep, pigs, chickens and to a lesser extent cattle. The West African Dwarf (WAD) goat is the predominant goat breed found in the state with few other goat breeds. The major animal husbandry practice in the state is the semi-intensive and seasonal confinement system. The animals are allowed to fend for themselves post-harvest during dry season but are taken out for browsing or tethered during the day in the rainy season and are brought to the house in the evening.

Method of sample collection and serological analysis: Goats sera from six purposively selected communities comprising three different local government areas were screened for antibodies based on perceived risks like histories of infertility, abortion, still birth and poor-doer-syndromes as complained by the owners. Two communities each were identified from the three selected local government areas under investigation. Households and animals sampled were selected by combination of systematic random sampling, owner’s consent and the perceived risks. No history of brucellosis vaccination in animals was reported in the regions. The location of animal, sex, age, body score, husbandry system, herd size, mating system and source of buck for mating were studied variables recorded. About 5 mL of blood was aseptically collected by means of jugular venipuncture then placed in a slant position inside cooler and kept at room temperature for 3-4 h to clot and separate into serum. The sera harvested were then properly labeled and stored in the freezer at -20°C until used. Sera were then serologically tested for Brucella antibodies using standard Rose-Bengal test procedure (OIE., 2009a, b).

Statistical data analysis: All data were statistically analyzed with Epi Info 7 software, (Centers for Disease Control and Prevention, CDC, Atlanta, USA). Descriptive statistics was done using Chi-square statistical test and p<0.05 was considered significant. Mantel-Haenszel common Odds Ratio (OR) estimates were also reported alongside their 95% Confidence Intervals (CI).

RESULTS

The result is presented in Table 1. Overall, 11.9% (n = 22/185) of the goats screened were seropositive to Brucella antibodies. Seropositivity was comparatively highest in emaciated goats. Emaciated goats were also 2.9 times more likely to be seropositive than those with good body condition. Among the mating system category, uncontrolled mating was 1.2 times more likely to be seropositive to Brucella antibodies than controlled mating.

Table 1:	Prevalence of Brucella antibodies in the goats screened based on the studied variables
RBT+ve: Rose-Bengal test positive samples, CI: Confidence interval for OR, 1.0*: Reference value, X2: Chi-square, n: Number

Furthermore, seropositivity was not significantly (p>0.05) associated with local government area (p = 0.710), sex (p = 0.250), age (p = 0.830), number of goats in a household (p = 0.112) and husbandry system adopted by the household (p = 0.853), but was statistically significant for source of buck used in mating does (p = 0.012).

DISCUSSION

The findings of this study revealed 11.9% seroprevalence of Brucella antibodies hence providing valuable preliminary information on caprine brucellosis in the studied areas. This prevalence is similar to 12.0% by RBT reported in slaughtered goats (Shima, 2014) and 13.7% by RBT reported in goats from Oju local government (Ijale et al., 2014) in Benue State. Again, the prevalence is similar to 10.9% reported in goats from Sokoto State (Junaidu et al., 2010) and 12.9% in Ogun State (Talabi et al., 2013), but lower than 45.75% reported in goats from Abeokuta, Ogun State (Ojo et al., 2007) and 25.8% from Kaduna State (Kaltungo et al., 2013) in Nigeria. The lowest prevalence rate compared to our study is 1.8% reported in goats from Enugu State, Nigeria (Onunkwo et al., 2009). Differences in brucellosis prevalence from different geographical locations could be influenced by seasons in which the studies are conducted, serological tests used, management systems, mixing with other animals, source of animals sampled. In the present study, the differences observed in seroprevalence among the studied areas might have been influenced by husbandry system such as communal grazing and watering areas, mixing with other animals, segregation of animals, use of rangelands and large number of animals in a particular region.

Although sex was not significant (p = 0.250) for seropositivity to Brucella antibodies, male goats were more seropositive as compared to female goats, which is in agreement with earlier report (Adamu et al., 2012). While, some findings indicate no association of Brucella antibody titers with sex, others have found higher brucellosis prevalence in female goats than in males (Muma et al., 2006; Akbarmehr and Ghiyamirad, 2011; Negash et al., 2012). Higher incidence of brucellosis in female animals has been ascribed to allantoic factors such as erythritol, steroid hormones and other substances which stimulate Brucellae growth (Keppie et al., 1965; Radolf, 1994). In the present study, the higher seroprevalence in bucks may not be unassociated with high libido, borrowing of bucks with unknown brucellosis history and indiscriminate mating.

Seropositivity to Brucella antibodies was not significantly (p = 0.830) associated with age of the goats which agrees with the report from previous study (Ashagrie et al., 2011). However, the absence of statistically significant association between seropositivity and age could be an indication that all ages had equal likelihood of being infected with Brucella organisms. One important factor for the equal susceptibility could be exposure to poor management. Contrariwise, young animals may be exposed to Brucella infection early in life through suckling from an infected dam or sharing of contaminated environments. It has been documented that infection with Brucella organisms increases with age as most infected animals remain infected for life (Gul and Khan, 2007). Sex hormones and erythritol concentrations increases with advancing age and sexual maturity hence, creating more enabling conditions for the growth and multiplication of Brucella organisms in older animals (Amin et al., 2005; Radostits et al., 2007; Gul and Khan, 2007).

Semi-intensively reared goats were more seropositive compared to goats reared under seasonal confinement, which agrees with the finding of Muma et al. (2006). This could be due to Brucella contaminations, which could occur within the confined space. In another study, brucellosis was found to be more prevalent in extensively reared goats possibly, because the goats under this setting have higher probability of coming in contact with other infection sources or infected animals (Teshale et al., 2006).

Seroprevalence increased with increasing number of goats in the household studied. Increase in herd size intensifies the chance of contacts between animals, creating more chances for infection especially during calving and abortion when most Brucella contaminations likely occur (Gameel et al., 1993). Uncontrolled mating was 1.2 times more likely to predispose goats to brucellosis just as source of buck for mating was significantly (p = 0.012) associated with seropositivity while, indiscriminate use of any available source of buck for mating accounted for the highest prevalence. Emaciated goats were 2.9 times more likely to be seropositive compared to apparently healthy goats, possibly, because co-exposure to other debilitating conditions such as, helminthosis and poor nutrition may further suppress the immunity.

CONCLUSIONS

The moderately high prevalence of Brucella antibodies in the household goats investigated portends high risk of transmission to members of the households as both children and adults within the household often times have contacts with these animals. The finding of high prevalence in unvaccinated animals of this kind indicates occurrence of natural infection. To mitigate brucellosis, appropriate control measures and public health awareness are encouraged.

ACKNOWLEDGMENTS

We are thankful to all the goat owners for giving us their consents to enroll their animals into this study.