Genetic diversity of Ehrlichia ruminantium in Amblyomma variegatum ticks and small ruminants in The Gambia determined by restriction fragment profile analysis

Faburay, Bonto; Jongejan, Frans; Taoufik, Amar; Ceesay, Ansumana; Geysen, Dirk

doi:10.1016/j.vetmic.2007.06.010

Cited by 25 publications

(24 citation statements)

References 27 publications

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“…Although Kerr Seringe and Sankat 430 were from geographically isolated countries (The Gambia and Ghana, respectively [24,25]), a high level of similarity in the sequences from these strains have been previously reported based on the analysis of the highly polymorphic map1 gene [8]. Therefore, using only these target genes might not be sufficient to enable the discrimination between closely related strains.…”

Section: Resultsmentioning

confidence: 99%

Multi-locus sequence typing of Ehrlichia ruminantium strains from geographically diverse origins and collected in Amblyomma variegatum from Uganda

et al. 2011

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BackgroundThe rickettsial bacterium Ehrlichia ruminantium is the causative agent of heartwater in ruminants. A better understanding of the population genetics of its different strains is, however, needed for the development of novel diagnostic tools, therapeutics and prevention strategies. Specifically, the development of effective vaccination policies relies on the proper genotyping and characterisation of field isolates. Although multi-locus sequence typing (MLST) has been recently developed, only strains from geographically restricted collections have been analysed so far. The expansion of the MLST database to include global strains with different geographic origins is therefore essential. In this study, we used a panel of reference strains from geographically diverse origins and field samples of E. ruminantium detected from its vector, Amblyomma variegatum, in heartwater-endemic areas in Uganda.ResultsA total of 31 novel alleles (six, four, six, three, two, five, three, and two for gltA, groEL, lepA, lipA, lipB, secY, sodB, and sucA loci, respectively) and 19 novel sequence types (STs) were identified. Both neighbour-joining and minimum spanning tree analyses indicated a high degree of genetic heterogeneity among these strains. No association was observed between genotypes and geographic origins, except for four STs from West African countries. When we performed six different tests for recombination (GeneConv, Bootscan, MaxChi, Chimaera, SiScan, and 3Seq) on concatenated sequences, four possible recombination events were identified in six different STs. All the recombination breakpoints were located near gene borders, indicating the occurrence of intergenic recombination. All four STs that localized to a distinct group in clustering analysis showed evidence of identical recombination events, suggesting that recombination may play a significant role in the diversification of E. ruminantium.ConclusionsThe compilation of MLST data set across the African continent will be particularly valuable for the understanding of the existing genetic diversity of field isolates in African countries. Comprehensive information on the degree of cross-protection between strains and further understanding of possible relationships between genotypes and phenotypes such as vaccine efficacy are expected to lead to the development of region-specific vaccination strategies.

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Section: Resultsmentioning

confidence: 99%

Multi-locus sequence typing of Ehrlichia ruminantium strains from geographically diverse origins and collected in Amblyomma variegatum from Uganda

et al. 2011

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“…Most vector-borne pathogen studies examining genotype co-infection to date either survey the circulating pathogen genotypes in an area or conduct competition assays among pairs of genotypes, frequently differing drastically in fitness (e.g., attenuated versus virulent, transmissible versus not transmissible) [2],[5],[11],[15],[19],[48]–[50]. Knowledge gaps exist regarding the role of the vector in supporting or restricting pathogen genotype diversity in a population.…”

Section: Discussionmentioning

confidence: 99%

Restriction of Francisella novicida Genetic Diversity during Infection of the Vector Midgut

et al. 2014

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The genetic diversity of pathogens, and interactions between genotypes, can strongly influence pathogen phenotypes such as transmissibility and virulence. For vector-borne pathogens, both mammalian hosts and arthropod vectors may limit pathogen genotypic diversity (number of unique genotypes circulating in an area) by preventing infection or transmission of particular genotypes. Mammalian hosts often act as “ecological filters” for pathogen diversity, where novel variants are frequently eliminated because of stochastic events or fitness costs. However, whether vectors can serve a similar role in limiting pathogen diversity is less clear. Here we show using Francisella novicida and a natural tick vector of Francisella spp. (Dermacentor andersoni), that the tick vector acted as a stronger ecological filter for pathogen diversity compared to the mammalian host. When both mice and ticks were exposed to mixtures of F. novicida genotypes, significantly fewer genotypes co-colonized ticks compared to mice. In both ticks and mice, increased genotypic diversity negatively affected the recovery of available genotypes. Competition among genotypes contributed to the reduction of diversity during infection of the tick midgut, as genotypes not recovered from tick midguts during mixed genotype infections were recovered from tick midguts during individual genotype infection. Mediated by stochastic and selective forces, pathogen genotype diversity was markedly reduced in the tick. We incorporated our experimental results into a model to demonstrate how vector population dynamics, especially vector-to-host ratio, strongly affected pathogen genotypic diversity in a population over time. Understanding pathogen genotypic population dynamics will aid in identification of the variables that most strongly affect pathogen transmission and disease ecology.

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“…Heartwater is a rickettsial disease of domestic and wild ruminants caused by Ehrlichia (formerly Cowdria) ruminantium, which represents a significant obstacle to the improvement of livestock production in the tropics and subtropics with mortality rates ranging from 20-90% in susceptible animals. The organism is transmitted by ticks of Amblyomma spp., and small ruminants are particularly at risk of acquiring the disease [54].…”

Section: Tick-borne Pathogens In Small Ruminantsmentioning

confidence: 99%

Economic and Health Impact of the Ticks in Production Animals

Hurtado¹,

Giraldo-Ríos²

2019

Ticks and Tick-Borne Pathogens

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Nowadays there is no doubt about the importance of production animals in the economy and food security of the population throughout the world. For an animal to be productive (cattle, small ruminants, swine or poultry) is needed to be in adequate health conditions. The health of these animals can be altered by the direct and indirect effects of ticks, causing significant losses in the production of meat, milk, eggs, leathers, and in many cases the death of the affected animals. The direct losses are related to the damage produced by the ticks when feeding on the blood of their hosts, while the indirect losses are related to the infectious agents transmitted by the ticks, and the costs associated to the treatment and control. It is important then, to know what are the economic and health impacts of ticks on the main production animals.

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Genetic diversity of Ehrlichia ruminantium in Amblyomma variegatum ticks and small ruminants in The Gambia determined by restriction fragment profile analysis

Cited by 25 publications

References 27 publications

Multi-locus sequence typing of Ehrlichia ruminantium strains from geographically diverse origins and collected in Amblyomma variegatum from Uganda

Multi-locus sequence typing of Ehrlichia ruminantium strains from geographically diverse origins and collected in Amblyomma variegatum from Uganda

Restriction of Francisella novicida Genetic Diversity during Infection of the Vector Midgut

Economic and Health Impact of the Ticks in Production Animals

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