Yersinia Pestis Infection Symptoms And Treatment

Yersinia Pestis is the causative organism for Plague. It is a gram negative, non motile, cocco bacillus. The virulence of the organism is related to its ability to produce exotoxins, endotoxins and many other toxins. Plague is a highly contagious, acute illness transmitted to humans by the bite of an infected rat flea. It is commonly seen in developing countries. However it has a worldwide distribution. Only occasionally in cases of pneumonic plague, human to human transmission may be seen. It was named so in the honour of Alexander Yersin, as he was the one who isolated the bacteria in the year 1894 during a pandemic which began in China. Plague is primarily a zoonotic disease which affects rodents, humans are incidental hosts. Wild rodents like field mice, gerbils, skunks, and other small animals are reservoirs of Yersinia Pestis. They are found in mountains, deserts, cultivated areas and forests in the temperate and tropical regions.

Man may come in contact with contact with rodents in the course of hunting, cultivation, harvesting and construction activities or whilst engaging in outdoor recreation. Outbreaks of plague are usually seasonal. The commonest and the most efficient vector of plague is the rat flea, X. cheopis but other fleas may also transmit the infection for e.g. X. astia, X. brasiliensis and Pulex irritans (human flea). Incubation period of bubonic plague is 2 to 7 days, septicemia plague is 2 to 7 days and pneumonic plague is 1 to 3 days.

Bubonic plague is the most common type of disease caused by Yersinia Pestis; the infected rat fleas usually bite on the lower extremities and inoculate the bacilli into the human host. The bacilli are taken up in the regional lymph nodes which enlarge. The patient may complain of fever, chills, headache, prostration and painful lymphadenitis. The lymph nodes suppurate in a short period of time and form buboes, most commonly in the groin. It may also develop in the axilla or neck, depending on the site of the bite of the flea. Bubonic plague does not spread from person to person.

Pneumonic plague shows an incidence of below 1 percent. It is a highly infectious disease and spreads from man to man by droplet infection. It is present in the sputum.

Septicaemic plague is rate, except in cases of accidental laboratory infections. In cases where the bubonic plague is fulminant, it may develop into septicaemic plague.

Diagnosis: Yersinia Pestis stains with Giemsa’s or Wayson’s stain. Blood culture can be done in order to grow the bacillus. Antibody studies can be done on acute and convalescent specimens of blood sera.

Treatment: Treatment must be started without waiting for confirmation of the diagnosis. If not treated promptly, plague has a mortality of nearly 50 percent and pneumonic plague has a mortality of 100 percent. The drug of choice is streptomycin (30 mg per kg of body weight daily) or intramuscularly in two divided doses for 7 to 10 days. Tetracycline orally can be given in 30 to 40 mg per kg of body weight daily.

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