Abstract:
Rat-bite fever is an over-looked, global zoonotic disease that has a mortality rate of up to 13%, if untreated.
Historically, this rat-borne disease has been attributed to one of two causative agents, Streptobacillus
moniliformis or Spirillum minus. Given the confirmed presence of multiple invasive Rattus host species,
high rat densities in urban, informal human settlements and increasing reports of rat bites in South Africa,
we undertook a retrospective assessment of Streptobacillus in rats sampled from 16 urban sites, in Gauteng,
the smallest but most populous Province in South Africa. Using a multi-gene PCR-sequencing approach,
we confirmed Streptobacillus presence in 50.9% of oral swabs from three rat species and the presence of
two Streptobacillus species, viz. S. moniliformis and S. notomytis. The two members of the cryptic Rattus
rattus species complex (R. rattus and R. tanezumi), which are morphologically indistinguishable from
each other, had markedly different colonization rates. Whereas 48.6% of rats from this species complex
were Streptobacillus-positive, only 32.3% of Rattus tanezumi were positive compared to 61.5% R. rattus.
Rattus norvegicus had an intermediate prevalence of 55.6%. Phylogenetic analysis of four gene regions
(16S rRNA, gyrB, groEL, recA) identified two discrete lineages; S. moniliformis occurred exclusively in
R. norvegicus, and S. notomytis was restricted to the two members of the R. rattus species complex; this
represents the first report of Streptobacillus in R. tanezumi. These results highlight a largely overlooked
zoonotic threat posed by invasive rats and confirm the presence of two discrete and potentially hostspecific
Streptobacillus lineages in South Africa.
