Brucellosis is a zoonotic bacterial disease caused by various Brucella species, which mainly infect cattle, swine, goats, sheep and dogs.²⁴ In the current study, prevalence of brucellosis in Rafha. Saudi Arabia in sheep, goats and camels was determined by RBPT, as well as, camel strains were identified based on a glycosyltransferase gene analysis. Sero-positivity was assumed to be attributable to infection of brucellosis since immunization has never been practiced in the area.

The findings showed that the disease spread among ruminants and it occurred at a higher rate in sheep. The detected prevalence of brucellosis in sheep (11.4%), is similar to that published in Saudi Arabia¹⁴ as well as in India.²⁵ It was slightly lower than that reported in other parts of the country, including western region (15.6%) and Makkah (12.3-14.2%).^7,8,26 Much higher seroprevalence (31.7%) was reported at Duhok in northern Iraq.²⁷ However, it was slightly higher than the reported one (7.3%) in Aljouf region, Saudi Arabia,¹⁵ and in Aseer and Jazan (5.1%) in southern Saudi Arabia,²⁸ also that found (8.3%) in India.²⁹ Nevertheless, none of tested sheep sera in Farasan Islands in the Red Sea in southwestern Saudi Arabia were found to be positive.³⁰ Discrepancy may be due to the breed involved, herd size, management, and seasonality of the disease.

The detected percent of caprine brucellosis (4.7%) is alike to previous records in Bangladesh.^31,32 However, Abdellatif et al. ¹⁴ detected much higher seropositivity (12.1%) in Hail, Saudi Arabia. Meanwhile it was 8.8%, in Medina.³³ A very low seroprevalence (0.6%) was detected in goats in Farasan Islands in Saudi Arabia ³⁰ which is expected due to the isolated nature of the island. Brucellosis is endemic in many countries, variable seroprevalence of the disease had been reported. A very high prevalence (34%) in goats have been detected in Iraq ²⁷ and (27.7%) in Jordan.³⁴ In Dhofar Province at Southern Oman, goat sera showed 13% seropositivity.³⁵ In India, 5.8% seropositivity was determined.²⁹ It was found to be 14.8% in North West Libya,³⁶ which was higher than our present study. In contrast, Rahman & Ahasan³⁷ declared that the rate of brucellosis was 1.98% in Bangladesh. Despite contradictions in the literature, reports showed that sheep was more likely to be reactive than goats,^38-40 which may be influenced by sampling, circulating strain, immunity of the species, management (animal, herd, farm), and/or owner’s awareness about the disease.^41-43 The occurrence of camel brucellosis (5.6%) was slightly comparable to the obtained results in Hail (6.2%)¹⁴ and Alzulfi, Saudi Arabia (6.5%) Salih et al, higher than that reported (3.5%.) at Aseer and Jazan in southern Saudi Arabia²⁸ and disagree with the previous data (1.9%) reported in Riyadh by Alshaikh et al. Variable seroprevalence were found in other Gulf countries, in Dhofar, Southern Oman, 3.4% of camel sera tested positive.³⁵ A far higher seroprevalence of brucellosis in camel sera (20.6%) was reported in Qatar.³⁵ The rate also contrast with that reported in Ethiopia (2.2%),⁴⁴ 4.1%,⁴⁵ and 3.37%.⁴⁶ Higher rate was recorded in Sudan ((37.5%) ⁴⁷ and Somalia (7%).⁴⁸ The exposure may be increased as a consequence of the intense animal rearing.⁴⁹ Furthermore, the infections can also spread due to the absence of control measures, mixed grazing of camel herds with other herds and animals in the pasture, and drinking points. All cattle sera in the current study were seronegative, it may be related to the number of animals tested because cattle were not bred in the region. Previous research reported bovine brucellosis as 18.1% in Jordan,¹² 1.9% in China,⁵⁰ 6.3% in Pakistan.⁵¹ Seroprevalence was found to be variable depending on sampling size, species, sex and size of herd.³

Sex wise, seroprevalence was comparable to the previous reports.^15,52 But it differs with other literature.^34,53,54 Difference may be due to the immune response or the interaction of other risk factors. Age-level showed that was higher in adult animals, it’s supported by previous research.^15,40 It may be owing to sex hormones, which may stimulate the growth of the bacteria, and tend to increase in concentration with age and sexual maturity. This might be true since older animals keep on in the flock for a long time, and they had a longer duration of contact. The higher percentages in naimee breed may be due the number of animals tested.

Analysis of data revealed significant correlation between seroprevalence of Brucella spp. and species, sex and age. In contrary, there was no association between the prevalence and animal breed. Results were in accordance to that observed by Rahman et al. However, it opposed with Akhter et al.⁵⁵ who found that none of these factors was linked with brucellosis. Inconsistency may be attributed to variance in the risk factors involved at both animal and herd level.⁵⁶

Traditional identification of brucellosis depends on the isolation of the bacteria.⁵⁷ Owing to various restrictions in the isolation of the bacteria including requirement for biosafety facilities, workers expertise, and hazard of contamination, numerous molecular procedures to identify and discriminate Brucella species have been developed.⁵⁸ In the present investigation, camel strains were identified as B. melitensis based on glycosyltransferase gene amplification and sequencing. Comparative analysis of the nucleotide sequence among camel strains exhibited 96.2-100% similarity with multiple nucleotide substitutions and deletions. Phylogenetic analysis based on Glycosyltransferase gene sequence to clarify the genetic relation between local strains and other sequences deposited in GenBank. Unfortunately, there were no sequences of the Glycosyltransferase gene of the Brucella from Saudi Arabia found in GenBank to be added in the tree. Analysis display Brucella strains in two branches, Rafha strains clustered in one group together with other strains. The results agreed with Etemady et al., who report considerable genetic diversity among B. melitensis and conservation of B. abortus strains.