A dog-associated primary pneumonic plague in Qinghai Province, China

Background. Primarypneumonicplague(PPP)causedbyYersiniapestisisthemostthreateningclinicalformofplague. An outbreak was reported in July 2009 in Qinghai Province, China.Methods. This outbreak was investigated by clinical, epidemiological, bacteriological, and immunologicalmethods. Multilocus variablenumber tandem repeat analysis (MLVA) was used to track the source of the outbreak.Results. The index case, a patient with PPP, contaminated 11 close contacts. All the 12 cases, including theindexpatient, experiencedsuddenonsetof fever, headache,and productivecoughingwithbloody sputum.Threeofthem died. Nevertheless, another 61 direct and 256 indirect contacts were not infected during the 2-weekquarantine. Antibodies to F1 antigen were detected in 9 survival cases, with a 4-fold increase in titers in serumsamples collected at different periods. Seven strains of Y. pestis were isolated from dogs and patients. Fieldinvestigation and MLVA of the isolated strains revealed that this outbreak was started by a deceased dog.Conclusion. Dogs are believed to be an indicator animal for plague surveillance, but their association with PPPis rare. Our results provide evidence for this possibility, which suggests the public health significance of dogs asa source of plague.Plague, caused by Yersinia pestis, was classified asa reemerging infectious disease by the World HealthOrganization (WHO) in the early 1980s, because thereported cases around the world were increasing atthat time. There are different forms of plague, in-cluding bubonic and pneumonic, and the latter is themost threatening clinical form. Primary and second-arypneumonicplagueshavebeenwell-documentedinhistory.Theprimarypneumonicplague(PPP)out-breaks in Oakland in 1919, Los Angeles in 1924 [1],Manchuria during 1910–1911 [2], and Madagascar in1957 are the most frequently cited ones. PPP was alsoreported recently in the United States, India, Uganda,Zambia, Ecuador, and Madagascar [3–11]. BecausePPP progresses so rapidly that the patients often re-ceived a diasgnosis or were suspected to have plagueonly in the late stage of the disease, most of the PPPcases were reported on the basis of retrospectiveepidemiological investigations with only some ofthem confirmed by bacterial isolation and antibodydetection.On29July2009,asuspectedPPPoutbreakinXinghaiCounty, Qinghai provinceof China,was reportedtotheQinghai Ministry of Health by China’s public healthemergency reporting system. The next day, a group ofplague experts, including epidemiologists, bacteriolo-gists, doctors, and management officers, were sentout for further investigation in the Xinghai CountyTibetan (XCT) hospital, where the suspected patientshad been admitted.