Comparative Analysis of Tick-Borne Relapsing Fever Spirochaetes from Ethiopia and Nigeria

In recent decades, the reports of tick-borne relapsing fever (TBRF) spirochaetes and its tick vectors have been increasing in Africa. Soft ticks of the Ornithodoros genus are the predominant vector for these spirochaetes and are endemic in many regions in Africa including East and West Africa. While TBRF of veterinary importance are exclusively transmitted by hard ticks. Despite this, TBRF is still a neglected disease in many regions such as Nigeria and Ethiopia where the disease epidemiology is still largely unknown. In Nigeria, O. savignyi ticks infected with a human TBRF specie Candidatus B. kalaharica has been reported. While in Ethiopia, the agent of relapsing fever is the louse-borne relapsing fever (LBRF) that is endemic in some parts of the country, with no evidence of TBRF available.

To demonstrate the presence of TBRF of clinical and veterinary importance in Nigeria, 550 livestock, 152 patients presenting with recurrent fever, 550 livestock sera, 71 dog sera, and 251 soft ticks of the genus’s Ornithodoros and Argas were sampled. Conversely, in Ethiopia, to demonstrate the possible coexisting of TBRF with LBRF, 312 Ornithodoros ticks were sampled from soil around cattle shelter. Samples were screened for Borrelia infection on RT-PCR, with reactive samples subjected to further confirmation on conventional PCR using the 16S rRNA flagellin B genes, and the 16S-23S intragenic spacer region of Borrelia genome. While ticks were identified to the molecular level using tick 16S rRNA and tick mtrrs genes. Borrelia infection rate in livestock from Nigeria after initial screening was 3.8% (21/550), and 14% (3/21) after final confirmation. While the prevalence of infection in ticks from Ethiopia was 3.5% (11/312), and 36% (4/11) upon final confirmation. No infection was reported in the patients recruited.

Sequencing analysis revealed the borreliae from Nigerian livestock as B. theileri ‘a bovine borreliosis” specie. Whereas the borreliae from the Ethiopian ticks was identified C. B. kalaharica, a human species. Phylogenetic analysis revealed the identity of the Ornithodoros ticks as O. savignyi with >98% similarity for the Nigerian ticks, while the Ethiopian species had a 94% similarity. Conspicuously, the Ethiopian ticks formed a sister clade from the Nigerian ticks and other O. savignyi species available in the GenBank. This raises the question of whether the Ethiopian ticks represent a distinct species. The Argas ticks were identified as A. persicus using the 16S rRNA gene sequences.
This is the first documented evidence of a C. B. kalaharica and its O. savignyi vector in Ethiopia. This is significant for both diagnostic and public health, as the possible coexisting of both RFs may likely increase the burden of the diseases. The gold standard for RF diagnosis in the country is microscopy, which is unable to differentiate between LBRF and TBRF. Concurrently, this is also the first report of TBRF in livestock from Nigeria.

This study has clearly revealed the possible coexisting of LBRF and TBRF in Ethiopia. With this evidence, additional research into the vector distribution and disease epidemiology is vital to better understand its true burden in the country. This applies for Nigeria as there is a need for additional research to determine the true clinical and veterinary significance of the disease, especially in high-risk areas where these ticks are known to be endemic.