Resumen de Yersinia pestis infection in dogs: 62 cases (2003–2011)
Objective—To describe the epidemiology, clinical signs, and treatment practices in dogs with Yersinia pestis infection in New Mexico.
Design—Retrospective case series.
Animals—62 dogs with plague in New Mexico.
Procedures—Confirmed case animals had isolation of Yersinia pestis from a clinical specimen, a positive direct fluorescent antibody test result, or a minimum 4-fold change between acute and convalescent serum antibody titers with clinically compatible illness. Retrospective review of cases of laboratory-confirmed plague from 2003 to 2011 was performed with a standardized chart abstraction form. Epidemiologic, clinical, and treatment data were evaluated.
Results—62 confirmed cases of canine plague were identified from 2003 to 2011. Most cases (85%) were confirmed by serologic titers alone or in conjunction with other testing methods. Clinical signs included fever (100%), lethargy (97%), anorexia (77%), lymphadenopathy (23%), vomiting (13%), diarrhea (8%), and abscesses (2%). Most case animals (73%) were treated with multiple antimicrobials. Sixty (97%) case animals survived; of the 2 nonsurvivors, one was euthanized and another died. Potential sources of exposure to Y pestis included hunting, rodent or rabbit exposure, and residence in rural areas.
Conclusions and Clinical Relevance—Results indicated that dogs with exposure to Y pestis can develop moderate to severe illness or die as a result of infection. Veterinarians practicing in and examining animals from the western United States need to be familiar with the epidemiology of plague and query owners about potential plague exposures when consistent clinical signs are present. Veterinarians are often the first to recognize signs of plague among sentinel populations and have the opportunity to intervene and prevent zoonotic disease transmission.
Plague, a bacterial zoonotic disease caused by Yersinia pestis, is transmitted by fleas and affects mammals on several continents, including North America.1 Portions of the western United States are known enzootic foci of sylvatic plague, having a diversity of susceptible rodent and flea species, and mild weather that favors the maturation and vector efficiency of fleas.2 Results of a study3 in New Mexico indicate plague incidence rises with increased winter-spring precipitation, which results in increases in populations of rodents and other mammals serving as hosts for plague-infected fleas and consequent flea survival. In New Mexico, the most common hosts from which Y pestis have been isolated include prairie dogs, ground squirrels, mice, wood rats, rabbits, hares, and chipmunks.4,5 During epizootics, plague can spread to susceptible or accidental hosts.2 Transmission of plague to domestic carnivores, including cats and dogs, usually occurs through ingestion of infected animal tissue or a flea bite.6 Plague-infected domestic animals can be a source of human infection.7,8 Among domestic species, cats often receive attention for their role in direct transmission of plague to humans; however, dogs play an important role in the epidemiology of plague transmission by serving as a mechanical vector for plague-infected fleas.5,7,9–11 Dogs have been described as resistant to plague infection, and clinical illness in dogs is believed to be less common than clinical illness in cats.12,13 Transient mild to moderate febrile responses have been seen in dogs with experimental Y pestis infection along with other clinical signs of illness, including lethargy.14 Among naturally infected dogs, clinical signs reported in the literature include lethargy, pyrexia, and lymphadenopathy (buboes).1,15 In New Mexico, case reports15 indicate dogs have clinical illness more often than previously reported. After infection, domestic dogs have been reported to maintain antibody titers for up to 6 months.16,17 Domestic dogs in enzootic areas are exposed to Y pestis and might become clinically ill; however, to our knowledge, a comprehensive study of the prevalence and clinical illness characteristics of plague among domestic dogs has not been conducted.
Surveillance for plague among domestic dogs in New Mexico is conducted through laboratory-based surveillance. Plague in animals is a reportable condition in New Mexico. Veterinarians are encouraged to test domestic animals for plague if they have consistent clinical signs, including fever of unknown origin and a history of exposure to rodents, rabbits, or fleas, and to report suspect cases to public health authorities. Diagnostic testing for plague in domestic dogs is offered by the New Mexico Department of Health Scientific Laboratory Division and is performed by use of 3 methods: isolation of Y pestis through culture; DFA testing of tissue imprints on slides, lymph node aspirates, throat or wound swab specimens; or a 4-fold or greater change in titer between acute and convalescent serologic samples drawn preferably, at least 14 days apart.
Treatment for plague has been described in the human literature; several antimicrobials (eg, doxycycline, gentamicin, and ciprofloxacin) have in vitro efficacy and are successfully used in the treatment.18–21 Limited data are available regarding the efficacy of antimicrobials available to veterinarians to treat plague in domestic animals; most data are extrapolated from human medicine and research involving mouse studies.21,22 The primary objectives of the study reported here were to characterize clinical signs of canine plague and to describe treatment practices and the epidemiology of plague among domestic dogs in plague-enzootic New Mexico.
