Risk factors of brucellosis seropositivity in Bactrian camels of Mongolia.

Background: More information on brucellosis epidemiology in Bactrian camels is needed due to their growing economic and livelihood importance for herders and renewed efforts in Mongolia to eliminate brucellosis through mass vaccination of ruminants excluding camels. Brucellosis prevalence in camels increased over the past two decades. Random multi-stage cluster surveys were done in the Eastern provinces of Dornod and Sukhbaatar in 2013 and 2014 and in the Southern & Western provinces of Dornogobi, Umnogobi and Khovd in 2014 and 2015. A total of 1822 camels, 1155 cattle, and 3023 small ruminant sera were collected and tested with the Rose Bengal Test. In addition, 195 vaginal swabs and 250 milk samples for bacteriological culture were taken from livestock with history of abortion.

Results: The overall apparent seroprevalence in camels was 2.3% (95% confidence interval 1.6-3.3). The main risk factor for camel seropositivity was being in an Eastern province when compared to Southern & Western provinces (odds ratio 13.2, 95% CI 5.3-32.4). Camel seroprevalences were stable over the two consecutive survey years, despite introduction of ruminant vaccination: 5.7% (95% CI 3.1-10.2%) and 5.8% (3.3-10.1%) in Eastern provinces and 0.4% (0.2-1.2%) and 0.5% (0.1-2.0%) in Southern & Western provinces. We isolated Brucella abortus from camels and cattle. Camel seropositivity was associated to keeping cattle together with camels. Monitoring of vaccination campaigns showed that coverage in cattle was insufficient because animals could not be adequately restrained.

Conclusions: The present study reveals that brucellosis is present with important seroprevalence in Mongolian camels and was endemic in Eastern provinces. Camel herd seropositivity was most closely associated to infection in cattle. Longer term monitoring is needed to assess whether camel seroprevalance decreases with ongoing vaccination in Mongolia. This should be coupled with further confirmation on Brucella spp. isolates. To date, only Brucella abortus was isolated, but camels are also susceptible to Brucella melitensis. Clear verbal and written information on disease prevention in livestock and household members is important, particularly for remote camel herders who had only moderate knowledge on brucellosis epidemiology and preventive measures.