Plague caused by Yersinia pestis, has persisted in Brazil in several natural foci spread throughout rural areas in the States of Ceara, Paraiba, Pernambuco, Piaui, Rio Grande do Norte, Alagoas, Bahia, Minas Gerais and Rio de Janeiro. Nationwide surveillance of plague in Brazil based on serological testing started in 1983. We now present an update report of the examinations carried out in our laboratory from 1983 to 1992. The passive hemagglutination test for antibodies against fraction 1A antigen of Y. pestis and the passive hemagglutination inhibition control were employed for testing a total of 220,769 sera. Samples analyzed included 2,856 sera from clinically diagnosed plague cases or suspects, 49,848 sera from rodents of 24 species and 2 species of small wild carnivores (marsupials), 122,890 sera from dogs, and 45,175 sera from cats. Specific antibodies were found in 92 (3.22%) human sera; 143 (0.29%) sera from rodents of 8 species and from the two species of marsupials, 1,105 (0.90%) sera from dogs and 290 (0.64%) sera from cats. The presence of significant levels of specific anti-F1A antibodies among rodents and wild or domestic carnivores (dogs and cats) indicates that all the Brazilian plague foci remain active in spite of the absence of human cases in some of them.
During a plaque outbreak in the Borborema Plateau focus (Paraiba), bacteriological and serological studies were carried out in material from 452 patients (48 positives), 1,938 rodents and other small mammals (75 positives), 4,756 dogs (141 positives) and 2,047 cats (57 positives) obtained from 41 counties (out of which, 21 produced positive samples). Twenty Yersinia pestis strains isolated from material from 3 patients and 17 rodents, displayed biochemical reactions, virulence factors, antibiotic susceptibility and animal experimental pathogenicity similar to those observed in strains previously isolated. According to our findings this recent plague outbreak did not exhibit different factors from those observed during prior outbreaks in other plague foci in the northeast of Brazil.
To clarify the pathogenesis of oral plague infection, we studied the susceptibility of three species of rodents to intragastric inoculation of Yersinia pestis, described the pathology and progression of infection, and measured antibody responses to fraction IA antigen of Y. pestis. The 50% lethal doses of bacteria by intragastric inoculation for Mus musculus, Zygodontomys pixuna, and Rattus rattus were log10 = 6.32, 5.46, and 9.62, respectively, which were at least 1,000-fold higher than the values obtained by subcutaneous inoculation. M. musculus was shown to be susceptible to lethal infection also when bacteria were ingested in drinking water. Microscopic pathology was consistent with heavy systemic infection. Quantitative cultures of tissues at different times after intragastric inoculation revealed that infections of blood, liver, and spleen preceded infections of Peyer's patches and mesenteric lymph nodes. Stool cultures were negative. The strain of Y. pestis used for inoculation was killed when exposed to a buffered solution at pH less than or equal to 3. Antibody responses were observed in some of the surviving rodents after intragastric challenge. These results showed that Y. pestis was an effective oral pathogen that produced fatal systemic infections and self-limited infections with immunity but did not produce enteric pathology or lead to fecal excretion of bacteria.
O presente trabalho mostra a histopatologia da infecção pela Yersinia pestis, entre as diferentes espécies de roedores silvestres e comensais (cricetídeos, equimídeos, murídeos e cavídeos) que ocorrem na zona endêmica de peste do Nordeste do Brasil. Estes roedores foram encontrados naturalmente infectados nos campos ou inoculados experimentalmente no laboratório (vias percutânea, subcutânea ou picada de pulgas) com cepas locais e/ou estrangeiras de Yersiniapestis. Quase todos os animais, exceto alguns dos cavídeos, desenvolveram a forma bubosepticêmica da peste. Entre as lesões encontradas, a necrose coagulativa multifocal do fígado, a pneumonite intersticial aguda difusa e a atrofia linfoide do baço, podem, por sua constância, ser consideradas como os principais indicadores histológicos da infecção pestosa, embora estas lesões não sejam exclusivas da peste. A diversidade e a intensidade das lesões entre os Zygodontomys lasiurus pixuna, podem explicar a mortalidade elevada desta espécie e a disseminação da peste nos focos naturais do Nordeste brasileiro. Cricetídeos e murídeos mostraram alterações histopatológicas qualitativamente semelhantes. A resistência dos cavídeos à infecção pestosa foi evidenciada pela sobrevida desses roedores à fase aguda da infecção e pelo desenvolvimento de uma reação histiocitária interna, delimitando as áreas abscedadas. è possível que estas lesões crônicas abriguem bacilos virulentos, que permitirão a reinfecção periódica das pulgas e conseqüente reativação do processo epizoótico.
Soros de carnívoros domésticos (cães e gatos), roedores, e pacientes suspeitos de peste, obtidos durante dois surtos de peste humana e de roedores, um em 1982, no foco da Serra de Baturité/CE e o outro, em 1986, no Planalto da Borborema/PB e soros de carnívoros e de roedores do foco da Chapada do Araripe/PE, obtidos, em 1986, na ausência de casos humanos, foram analisados pelas micro técnicas de hemaglutinação passiva para anticorpos específicos, contra a fração antigênica purificada - F1A - de Yersinia pestis e inibição da hemaglutinação. Os altos percentuais de carnívoros, sorologicamente, positivos encontrados durante os surtos de peste humana, confirmam que esses animais estão implicados no ciclo epidemiológico da peste, nos focos do Nordeste do Brasil, e representam valiosos indicadores das atividades da infecção.
Blood sera were obtained from domestic carnivores (dogs and cats), rodents, and plague suspected humans during two Brazilian plague outbreaks that have occurred in Baturité Mountain focus, (Ceará state), in 1982 and Borborema Plateau focus, (Paraíba state), in 1986. Blood sera were also obtained from animals on Araripe Plateau focus, (Pernambuco state), during 1986, when human cases of plague had not been reported. The samples were analysed by passive haemagglutination test for antibodies against the fraction - F1A - of Yersinia pestis concomitant with the passive haemagglutination inhibition test. The high percentage of seropositive carnivores found during the plague outbreaks indicates that these animals may also be involved in the epidemiological cycle of plague in Brazil, and could represent a valuable indicator of the infection activity
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