Ehrlichia ruminantium variants which do not cause heartwater found in South Africa

Abstract

In 1994 a batch of apparently healthy goats was selected for intended export to the USA from a heartwater-free and vector tick-free region of South Africa. The animals were tested serologically for heartwater, using either or both an IFA and an ELISA test, and 52% were found to be serologically positive. A PCR assay based on Ehrlichia ruminantium 16S gene sequences gave positive results for 54% of the animals, suggesting that apparently non-pathogenic E. ruminantium variants existed in this heartwater-free area. To identify and characterise the agents responsible for the positive serological and PCR results, ticks and animal blood samples were collected from two of the three farms involved in the original survey during two successive seasons of expected peak tick activity. Ticks were kept alive for a minimum of 3 weeks to allow digestion of any blood meal before being processed.Over the two seasons, 28% of the livestock and 15% of the ticks sampled were found to be carrying E. ruminantium. E. ruminantium 16S and pCS20 sequences were detected in all of the four tick species collected from the livestock (Rhipicephalus evertsi evertsi, Rhipicephalus evertsi mimeticus, Hyalomma truncatum, Hyalomma marginatum rufipes),suggesting that some of the species may act as vectors. Animals generally carried multiple E. ruminantium 16S genotypes, whereas ticks rarely carried more than one.Infection levels in both animals and ticks were too low to generate a marked response openUP when a blood stabilate was sub-passaged in a clean sheep, preventing the subsequent establishment of any of the organisms in culture.

Molecular detection of Ehrlichia ruminantium infection in Amblyomma variegatum ticks in The Gambia

“…Similar findings were also reported in a recent study (Allsopp et al 2007), in which the pCS20 PCR failed to give amplicons from ticks from which E. ruminantium 16S sequences were obtained; this finding was attributed to the presence of polymorphisms in one or both of the pCS20 nested amplification primer target sites thus preventing effective hybridization and chain extension. The same authors (Allsopp et al, 2007) reported the detection of pCS20 and 16S sequences in animals and non-Amblyomma tick species in a heartwater-free area in South Africa (Northern Cape) and suggested the presence of a non-pathogenic variant of E. ruminantium in this area.…”

“…Indeed, the map1 gene of E. ruminantium has been reported to exhibit a high degree of sequence polymorphism (Reddy et al 1996;Allsopp et al 2001), whereas the lack of amplification by pCS20 primers (AB128/AB129 primers, Mahan et al 1992) could be attributed to the design of these primers in a comparatively less conserved region of the pCS20 sequence (Van Heerden et al 2004). Similar findings were also reported in a recent study (Allsopp et al 2007), in which the pCS20 PCR failed to give amplicons from ticks from which E. ruminantium 16S sequences were obtained; this finding was attributed to the presence of polymorphisms in one or both of the pCS20 nested amplification primer target sites thus preventing effective hybridization and chain extension. The same authors (Allsopp et al, 2007) reported the detection of pCS20 and 16S sequences in animals and non-Amblyomma tick species in a heartwater-free area in South Africa (Northern Cape) and suggested the presence of a non-pathogenic variant of E. ruminantium in this area.…”

“…Thus, although the pCS20, map1 and 16S PCRs have been used to detect E. ruminantium infection in ticks or animals (Mahan et al 1998;Peter et al 1995Peter et al , 2000Allsopp et al 1999;Kock et al 1995;Allsopp et al 2007), this is the first time the 3 molecular assays, pCS20, map1 and RLB, designed in a nested approach for increased sensitivity, have been applied to vector populations, A. variegatum field ticks, to evaluate their comparative performance in detecting E. ruminantium infection. This study demonstrated that the nested pCS20 PCR is a more sensitive diagnostic tool for the detection of E. ruminantium infection than either the nested map1 PCR or nested Anaplasma/Ehrlichia RLB.…”

Phylogeography and Demographic History ofAmblyomma variegatum(Fabricius) (Acari: Ixodidae), the Tropical Bont Tick

“…These findings suggest that several strains of E. ruminantium were introduced with A. variegatum in the 19th century . As single animals reportedly can be infected with multiple E. ruminantium genotypes (Allsopp et al 2007) and be healthy carriers for months (Andrew and Norval 1989), the concomitant importation of different pathogenic genotypes is unsurprising.…”

Molecular screening of ticks for the presence of Rickettsia species: A public health concern

“…There are scanty reports on the ability of this species to transmit diseases in both humans and animal. However, it is a known vector agent of the protozoan Babesia bigemina, Crimean-Congo hemorrhagic fever virus (CCHFV), and Ehrlichia ruminantium [55][56][57]. Mediannikov et al [54] has reported on the ability of R. evertsi evertsi to transmit rickettsial agents in ticks that were collected in Senegal.…”