RESUMO
Heartwater is an economically important disease of ruminants caused by the tick-transmitted rickettsia Cowdria ruminantium. The disease is present in Africa and the Caribbean and there is a risk of spread to the Americas, particularly because of a clinically asymptomatic carrier state in infected livestock and imported wild animals. The causative agent is closely related taxonomically to the human and animal pathogens Ehrlichia chaffeensis and Ehrlichia canis. A dominant immune response of infected animals or people is directed against variable outer membrane proteins of these agents known, in E. chaffeensis and E. canis, to be encoded by polymorphic multigene families. We demonstrate, by sequence analysis, the map1 encoding the major outer membrane protein of C. ruminantium is also encoded by a polymorphic multigene family. Two members of the gene family are located in tandem in the genome. The upstream member, orf2, is conserved, encoding only 2 amino acid substitution among six different rickettsial strains from diverse locations in Africa and the Caribbean. In contrast, the downstream member, map1, contains variable and conserved regions between strains. Interestingly, orf2 is more closely related in sequence to omplb of E. chaffeensis than to map1 of C. ruminantium. The regions that differ among orf2, map1, and omp1b correspond to previously identified variable sequences in outer membrane protein genes of E. chaffeensis and E. canis. These data suggest that diversity in these outer membrane proteins may arise by recombination among gene family members and offer a potential mechanism for persistence of infection in carrier animals.(AU)
Assuntos
Estudo Comparativo , Proteínas da Membrana Bacteriana Externa/genética , Sequência Conservada , Ehrlichia ruminantium/genética , Família Multigênica/genética , Variação Genética , África , Sequência de Aminoácidos , Região do Caribe , Bases de Dados Factuais , Ehrlichia chaffeensis/genética , Genoma Bacteriano , Dados de Sequência Molecular , Fases de Leitura Aberta/genética , Reação em Cadeia da Polimerase , Polimorfismo Genético , Alinhamento de Sequência , Homologia de Sequência de AminoácidosRESUMO
In Culex pipiens mosquitoes, AChE1 encoded by the locus Ace.1 is the target of organophosphorous and carbamate insecticides. In several resistant strains hompzygous for Ace.1RR, insensitive AChE1 is exclusively found. An unusual situation occurs in two Caribbean resistant strains where each mosquito, at each generation, displays a mixture of sensitive and insensitive AChE1. These mosquitoes are not heterozygotes, Ace.1RS, as preimaginal mortalities cannot account for the lethality of both homozygous classes. This situation is best explained by the existence of two Ace.1 loci, coding, respectively, a sensitive and insensitive AChE1. Thus, we suggest that in the Caribbean a duplication of the Ace.1 locus occurred before the appearance of insecticide resistance at one of the two copies.(AU)
