PLAGUE

PLAGUE


Plague is an acute, highly infectious disease transmitted to humans and animals by the bite of a rat flea. It has been known as bubonic plague and black death.



MORBIDITY: +




MORTALITY: + TO +++




ETIOLOGY: BACTERIAL


Plague is caused by Yersinia pestis, a gram-negative, bipolar-staining rod. Y. pestis is easily destroyed by drying or sunlight. It can survive for up to an hour when released into the air. Y. pestis is considered a potential biological weapon in aerosol form.



HOSTS


Rats, prairie dogs, rock squirrels, ground squirrels, chipmunks, and other burrowing rodents are the primary reservoirs for Y. pestis. Many species of fleas can act as vectors for Y. pestis, but the rat flea is the most important vector for the plague bacterium. Ticks and human lice have also been identified as possible vectors. In North America, where the plague is mostly seen in the western third of the United States and Canada, the ground squirrel, rock squirrel, and their fleas are the most common source of human infection. Rats and their fleas have not played a role in plague epidemics in the United States since the Los Angeles epidemic of 1924-1925. Fleas can readily infect cats and, less frequently, dogs. If cats develop a pneumonic plague, they can become a source of infection for people through aerosol transmission of the bacteria on droplets expelled during coughing. Cats, dogs, and rabbits can also bring the infected fleas into a home.



TRANSMISSION


Plague is characterized by periodic outbreaks in a rodent population. A flea transmits Y. pestis bacteria from one animal to another or to humans. When a flea takes a blood meal from an infected host, such as a ground squirrel, it also ingests some of the bacteria that are living in the blood of that host. The bacteria stay in the intestines of the flea, and when it takes another meal it deposits some of the Y. pestis organisms into a new host (Figure 29).


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FIGURE 29 Plague.


In a population of rodents, some of the rodents are resistant to Y. pestis infection, and others are highly susceptible. As the susceptible rodents become infected and die, the rodent population decreases, and the fleas will look to other animals, or people, as a blood source.


Transmission can also occur when a person or animal with pneumonic plague, which occurs when Y. pestis infects the lungs, coughs near another person or animal. The organisms ride on the droplets produced by the cough and are inhaled by another host.


A third method of transmission involves handling infected animals or carcasses. If the animal is infected, some of the bacteria could enter the human body through breaks in the skin. Hunters skinning animals are at risk for this type of transmission.

Related posts:

  1. ABOUT THE DISEASES
  2. CAMPYLOBACTERIOSIS (VIBRIOSIS)
  3. MYCOBACTERIUM INFECTIONS (TUBERCULOSIS)
  4. PSITTACOSIS

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Oct 1, 2016 | Posted by in EXOTIC, WILD, ZOO | Comments Off on PLAGUE

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