Prevalence and risk factors of Coxiella burnetii infection in cattle on farms in Limpopo province, South Africa

Abstract

Coxiella burnetii is a worldwide zoonotic bacterial pathogen and the causative agent for the zoonosis known as Q fever. The appearance of Q fever has been reported internationally and it is considered indigenous in most places in the world, but, in South Africa there are few studies of Q fever in livestock. This study aimed to determine the occurrence and prevalence of C. burnetii in farmed animals in Limpopo province, South Africa, and assess the risk of transmission to humans and animals. This cross-sectional study was conducted in the Capricorn, Sekhukhune, and Waterberg district municipalities of Limpopo. Blood samples were collected from the selected cattle (male and female) from the coccygeal veins into tubes; vaginal swabs, as well as sheath wash samples, were also collected. All of the farmers and farm workers were unaware of Q fever during the sampling process. A structured questionnaire survey was administered to the farmers to collect demographic data and potential risk factors for exposure of animals and humans to C. burnetii. The IDEXX Q-FEVER 2/strip ELISA kit was used to detect IgG antibodies to C. burnetii infection. Conventional PCR targeting the IS1111 gene fragment was used to determine the PCR prevalence. Data for ELISA and PCR were analysed separately using univariate logistic regression followed by multivariate logistic regression. To verify Coxiella IS1111 gene fragment amplification, seven of the PCR products were sent to Inqaba Biotechnologies for sequencing of both the forward and reverse strands using an ABI sequencer. Out of 383 cattle tested for antibodies against C. burnetii, the overall seroprevalence was 24.28% (93/383). Farms with a herd size > 150 had the highest seroprevalence of 70.37%, and a lower seroprevalence of 18.85% was observed in the herd size category of 1-50. Q fever prevalence by PCR in females was found to be 16.72% and 8.33% in males. Farms with a herd size greater than 150 had the highest PCR positivity of 44.44% and a PCR prevalence of 18.87% was observed in farms that fall under the category of 51-100 herd size. Commercial farms exhibited a prevalence of 18.14% of cattle testing positive by PCR and also a higher seroprevalence of 28.84% was observed in commercial farms. In the final multivariable logistic regression, local municipality (OR 1.09; 95% CI 1.00 - 1.20; P = 0.043) and herd size (OR 2.24; 95% CI 1.21 -4.15; P = 0.010) remained associated with C. burnetii seropositivity in cattle. Only abortion history (OR 0.31; 95% CI 0.11 0.89; P = 0.030) remained associated with C. burnetii positivity by PCR. Molecular detection of C. burnetii in sheath scrapings and vaginal swabs by PCR targeting the IS1111 gene revealed that 15.67% were positive and the amplicons were 146 bp in size. Of the seven sequences analysed on NCBI BLAST for sequence identity, all had similarities to C. burnetii transposase gene fragment, confirming molecular detection of the bacterium. In conclusion, we investigated the seroprevalence, PCR prevalence, and risk factors correlated with C. burnetii in cattle on farms in Limpopo province, South Africa. This study discovered that C. burnetii is widespread in the study areas (Capricorn, Waterberg, and Sekhukhune) and should be regarded as a possible source of human Q fever.