Plague (cont.)

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What causes plague?

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Infection with Y. pestis causes plague in humans. Y. pestis is a bacterium that is a gram-negative rod-shaped bacterium genetically related to Escherichia coli that resembles a "safety pin" when stained with certain chemicals and viewed with a microscope. In general, plague circulates in rodent populations where infected fleas on rodents transfer the bacteria to other rodents. When the rodent population invades human habitats or when humans invade rodent habitats, the infected fleas on the rodents will also bite humans. This flea bite begins the development of plague in an individual. However, once a human is infected, it is fairly easy for that person to infect other people with the organisms especially if they develop pulmonary infection because droplets containing Y. pestis from the lungs are expelled into the air and can infect other humans.

The most recent concern about the plague came from California in July 2013. A squirrel captured at Table Mountain campgrounds tested positive for plague. The findings prompted officials to eventually close three campgrounds, and squirrel habitats were dusted with flea powder. No human infections were detected. Since 1984, only four people have been reported to have been infected with plague in this California county.

How is plague spread?

Plague is a zoonotic (animal to animal) disease that can be spread to humans by several methods. The usual way humans encounter plague is from getting a flea bite from a flea that has previously been infected from biting an animal where the disease is endemic. Most often this is attributed to a plague-infected rat population, but it could be from many other animals such as mice, prairie dogs, squirrels, and other rodents. Unfortunately, even domestic cats and dogs can become infected and potentially may transmit the disease to humans. Dead animals can still contain many viable Y. pestis; humans can become infected when they handle these animals. People should use caution when touching touch dead animals or even getting close to them as they may have fleas looking for another warm (human) body to bite. Human-to-human spread occurs easily by people with pneumonic plague as they can spread infected droplets expelled from the lungs to other people or to objects that are subsequently touched by others. Individuals with bubonic or septicemic plague can also transmit the disease, usually by direct or indirect contact with infected body fluids or objects that come in contact with these fluids. Spread of plague can be facilitated when conditions arise that encourage rat populations to rapidly increase. For example, when cities reduce or fail trash pickup for any extended time period, a rat population may flourish, and so may the flea population. Consequently, human behaviors (warfare, economic failures, urban expansion, and others) may augment the development of plague.

Medically Reviewed by a Doctor on 10/30/2013

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