Seroprevalence and spatial distribution dynamics of Yersinia pestis antibodies in dogs and cats from plague foci in the State of Ceará, Northeastern Brazil

Abstract INTRODUCTION: In Brazil, the plague is established in several foci located mainly in the northeastern part of the country, where it alternates between active and quiescent periods. These foci in the State of Ceará have high epidemiological importance. In addition to other plague detection activities, plague areas can be monitored through serological surveys of dogs and cats (domestic carnivores), which, following feeding on plague-infected rodents, can develop mild to severe forms of the disease and produce long-lasting antibodies. This study aimed to characterize the circulation dynamics and spatial distribution of Yersinia pestis antibodies in dogs and cats in plague foci areas of Ceará. METHODS: An ecological study was conducted to analyze the temporal series and spatial distribution of secondary data obtained from domestic carnivore serum surveillance in Ceará's plague areas from 1990 to 2014. RESULTS: Joinpoint analysis revealed that the overall trend was a reduction in antibody-positive animals. The mean proportion of antibody-positivity during the whole study period was 1.5% (3,023/203,311) for dogs, and 0.7% (426/61,135) for cats, with more than 4% antibody-positivity in dogs in 1997 and 2002. Antibody titers ranging from 1/16 to 1/64 were frequent. Despite fluctuations and a significant reduction, in recent years, there were antibody-positive animals annually throughout the study period, and the localities containing antibody-positive animals increased in number. CONCLUSION: Yersinia pestis is actively circulating in the study areas, posing a danger to the human population.

Prevalência de anticorpos contra Yersinia pestis em carnívoros domésticos nos focos pestosos, do Estado do Ceará / Prevalence of antibodies against Yersinia pestis in domestic carnivores, in plague foci in the State of Ceará

Analisou-se a prevalência de anticorpos contra Yersinia pestis em carnívoros domésticos (cães e gatos) nas áreas pestígenas do Estado do Ceará, visando estabelecer a importância do monitoramento desses animais na rotina do Programa de Controle da Peste. No decênio 1997-2006, analisaram-se 146.732 amostras de soros (95.883 cães e 50.849 gatos), das quais 2.629 (2.234 cães e 395 gatos) revelaram-se positivas. A prevalência entre os cães (85 por cento) foi superior a dos gatos (15 por cento) em todo o decênio e locais, exceto em Ibiapina, em 1998. O significado desses achados ainda não foi determinado. Os estudos sobre a zoonose no Brasil pautaram-se por paradigmas que não contemplavam todos os elementos envolvidos na zoonose, impossibilitando a devida elucidação do papel desses carnívoros. O monitoramento da atividade pestosa, realizado exclusivamente por inquéritos caninos, pode redundar no desconhecimento progressivo da situação epidemiológica da peste, caso não sejam desenvolvidas pesquisas interinstitucionais suplementares.

The prevalence of antibodies against Yersinia pestis in domestic carnivores (dogs and cats), in plague areas in the State of Ceará, was analyzed to establish the importance of monitoring these animals within the routine practice of the plague control program. Over the decade 1997-2006, 146,732 serum samples were examined (95,883 from dogs and 50,849 from cats), of which 2,629 (2,234 from dogs and 395 from cats) proved to be positive. The prevalence among dogs (85 percent) was higher than among cats (15 percent) throughout the decade and in all places, except in Ibiapina in 1998. The significance of these findings has not yet been determined. Studies on this zoonosis in Brazil have been based on paradigms that did not cover all the elements involved in the zoonosis, thus making it impossible to properly understand the role of these carnivores. Monitoring of plague foci conducted exclusively by means of dog surveys may result in progressive lack of knowledge of the epidemiological situation of plague, if supplementary inter-institutional research is not developed.

The use of filter paper plasticized with polyvinyl alcohol-glutaraldehyde in ELISA

F1-antigen purified from Yersinia pestis was covalently linked to 5-mm diameter filter paper discs plasticized with polyvinyl alcohol-glutaraldehyde. These discs were used both for ELISA and dot-ELISA for the detection of anti-F1 IgG in rabbits. The best conditions were achieved using 1.25 µg of F1 antigen/disc, 3 percent w/v skim milk in PBS as blocking agent, anti-IgG peroxidase conjugate diluted 12,000 times, and serum from rabbits immunized or not against Y. pestis, diluted 6,400 times. The absorbance values obtained from the comparative study between this procedure and conventional ELISA were not significantly different but the low cost of the reagents employed in ELISA using the filter paper discs plasticized with polyvinyl alcohol-glutaraldehyde makes this method economically attractive.

The use of polyvinyl alcohol glutaraldehyde as solid-phase in ELISA for plague

Discs of polyvinyl alcohol cross-linked with glutaraldehyde were synthesized under acid catalysis (H2SO4). Then, the antigen F1 purified from Yersinia pestis was covalently linked to this modified polymer. Afterwards, an enzyme-linked immunosorbent assay (ELISA) was established for the diagnosis of plague in rabbit and human. The best conditions for the method were achieved by using 1.3µg of F1 prepared in 0.067 M phosphate buffer, pH 7.2, containing 1 M NaCl (PBS); anti-IgG peroxidase conjugate diluted 6,000 times and as a blocking agent 3 per cent w/v skim milk in PBS. The titration of positive rabbit serum according to this procedure detected antibody concentrations up to 1:12,800 times. The present method, the conventional ELISA and passive haemagglutination assay are compared.

Plague surveillance in Brazil: 1983-1992

A peste, infeccao pela Yersinia pestis, se mantem no Brasil, em varios focos naturais, disseminados na area rural, dos Estados do Ceara, Paraiba, Pernambuco, Piaui, Rio Grande do Norte, Alagoas, Bahia, Minas Gerais e Rio de Janeiro. Desde de 1983, o teste de hemaglutinacao passiva para anticorpos contra a fracao antigenica "F1A" de Y. pestis, vem sendo empregado ininterruptamente na vigilancia da peste nos focos brasileiros. A especificidade do PHA e controlada pelo teste de inibicao da aglutinacao. No periodo de 1983 a 1992 foram examinadas 220.769 amostras de soro, sendo 2.856 de origem humana, 49.848 de roedores pertencentes a 24 especies e de 2 especies de pequenos carnivoros selvagens (marsupiais), 122.890 soros de caes e 45.175 de gatos. Anticorpos especificos foram encontrados em 92 (3,22 por cento) dos soros humanos; 143 (0,29 por cento) soros de roedores de 8 especies e das duas especies de marsupiais, 1.105 (0,90 por cento) soros de caes e 290 (0,64 por cento) soros de gatos...

Inmunoprofilaxia de la peste / Immunoprophylaxis of the pest

La peste es una enfermedad infecciosa de tipo zoonótico que ha representado uno de los más serios problemas de salud pública en todo el mundo y debido a sus características pandémicas, mas que epidémicas, fue uno de los azotes de la antigüedad. Su agente etiológico es Yersinia pestis y la forma clínica más frecuente es una linfadentitis febril aguda o peste bubónica, aunque también se presentan formas septicémicas, neumónicas y meníngeas. En ausencia de tratamiento es sumamente mortal, pero esta se reduce notablemente si se instala una antibióticoterapia oportuna. La primera vacuna contra la peste fue elaborada por Haffkine en 1897 utilizando bacterias muertas; durante la Segunda Guerra Mundial y años después, en el ejército de los Estados Unidos se usó otro tipo de vacuna muerta con formalina y mediante sucesivas mejoras en los métodos de su producción se obtuvo, a partir de la cepa muy virulenta India 195/P de Y. pestis, la denominada vacuna contra la peste USP, medio E, ahora en uso; que se aplica en una primera serie de tres dosis intramusculares, la primera de 1 mL, seguida cuatro semanas más tarde de otra de 0.2 mL y 15 meses después de otros 0.2 mL. La efectividad de una serie primaria de vacunación nunca se ha medido en forma precisa; la experiencia en el campo indica que reduce la incidencia y severidad de la enfermedad posterior al piquete de pulgas infectadas. Se desconoce la protección que confiere contra la peste neumónica. Ya que la vacuna sólo aminora la sintomatología, se recomienda la administración profiláctica de antibióticos en todos los individuos que hayan estado expuestos al contagio, tengan o no antecedentes vacunales