Plague is a flea-borne zoonotic disease caused by the bacterium Yersinia pestis, which has been found on all continents except Australia and Antarctica.1-4 Most human cases of plague occur in Africa, particularly the Democratic Republic of Congo and Madagascar, and Peru.1 At least 17 US states have documented Y pestis infection in mammals or fleas.3,5 Most human cases in the United States occur in the southwest region (eg, New Mexico, Arizona, Colorado), followed by the Pacific region (eg, California, Oregon, Nevada).3,6,7
Y pestis is maintained in a sylvatic enzootic cycle in rural and semirural areas, primarily through flea transmission among certain wild rodents that experience low mortality rates.3,8,9 More than 200 species of mammals are susceptible to infection by Y pestis; morbidity and mortality varies by species, among individuals in a population,3 and by geographic location.3,10 Several species are more susceptible to plague and readily experience die-offs. These are referred to as “amplifying hosts.” Susceptibility of Peromyscus mice varies by species.11,12 Large die-offs of chipmunks, wood rats, and various species of ground squirrels have been documented.3 In the sylvatic epizootic cycle, outbreaks occur in more susceptible rodent species with consequential higher mortality rates8,9; these epizootics carry a high risk for infection in dogs, cats, and humans, as fleas search for new hosts after the die-off of their original hosts. This can result in a geographic hotbed of plague that should be avoided.8,13,14 Urban outbreaks can occur when Y pestis spreads from wild rodents to rats living near human habitation.4
Cats and dogs can become infected with Y pestis through consumption of infected small mammals and via flea bites.13,15,16 Infection in humans occurs primarily from flea bites8 but can occur through consumption3,17 or handling of infected animal tissue or body fluids3,18-21; direct or indirect contact with infectious exudates22; inhalation of respiratory droplets from humans, cats, or dogs with pneumonic plague5,8,18,23-26; cat bites5,27 and scratches5,28; and dog bites.21 Cats are more susceptible to plague than are dogs and pose a greater public health risk to humans.29 From 1977 to 1998, 23 cases of cat-associated plague—some involving veterinary staff members—occurred in 8 US states.5 Increased risk to humans comes from close contact with cats and dogs (eg, sharing a bed)15,30,31 and from pets bringing plague-infected fleas into the home.8,21,31
Review the impact, management, and implications of plague in its various forms.
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