Molecular prevalence and diversity of zoonotic bacteria of invasive Rattus from South Africa, with emphasis on the genera Rickettsia and Streptobacillus

Abstract

The study investigated the origin and diversity of the three matrilineally-defined invasive, commensal Rattus species, namely R. norvegicus, R. rattus and R. tanezumi known to occur in South Africa after routine identification of the species using molecular techniques. Subsequently, their role as potential zoonotic disease reservoirs in primarily urban environments with particular interest in their potential to transmit and spread zoonotic disease through direct contact as well as indirect contact through the urinary route were investigated. Bacterial prevalence and diversity were determined by PCR and nucleotide sequencing, respectively. Genetic diversity of Rattus in southern Africa was previously explored and despite additional samples being characterised in the present study, the genetic diversity in the southern African Rattus population remained relatively low when compared to global genetic diversity of the three matrilineally-defined Rattus species. Evidently, the observed genetic diversity is probably a result of a combination of introduction events and subsequent diversification which is possibly limited through interspecific competition with indigenous rodents. However, samples from the west and south coast of South Africa are under-represented in the data set and this would need to be addressed for better insight into the genetic diversity of the South African Rattus population. An overall bacterial prevalence of 49 % was observed in kidney samples using a 16S broad range PCR primer assay which when sequenced identified a diverse range of bacteria genera namely, Acinetobacter, Bartonella, Brochothrix, Rickettsia and Streptococcus. These bacteria are implicated in causing opportunistic infection and may contribute to food spoilage. Streptobacillus moniliformis is the etiological agent of rat-bite fever and Haverhill fever. A prevalence of 50.9 % was obtained in oral swabs while in kidney tissue this was only 6.3 %. Nucleotide sequencing of S. moniliformis revealed two S. moniliformis strains specific to the three matrilineally-defined Rattus hosts present in South Africa. Evidence of host specificity exists but could not be linked to the ecological factors tested. Rickettsial DNA was detected in only one R. tanezumi sample, corresponding to a prevalence of 0.9 %. Subsequent nucleotide sequencing and phylogenetic analysis confirmed the presence of pathogenic, Rickettsia felis. Consequently, Rattus is likely to be only an incidental host and the infection is probably maintained by their associated ectoparasites. The study has determined that introductions of some invasive, commensal Rattus have occurred relatively recently. Apart from the accompanying diseases introduced with them, the continuous influx of genetic diversity may influence rodent control efforts. In addition, the role of Rattus in the direct and indirect transmission and spread of zoonotic disease has been demonstrated, and their presence poses a public health and food security threat. Continuous disease surveillance and rodent control is crucial not only in urban areas where conditions are conducive to disease outbreaks but also at points of entry such as sea- and airports.