Yersinia pestis


Yersinia pestis

Description, Causes and Risk Factors:

Yersinia pestis is the causative agent of the systemic invasive infectious disease often referred to as the Black Death. The Y. pestis is an extremely virulent pathogen that is likely to cause severe illness and death upon infection unless antibiotics are administered.

In the past, Y. pestis has caused devastating epidemics during three periods of modern history; the Justinian Plague spread from the Middle East to the Mediterranean during the 6th-8th centuries AD and killed approximately 25% of the population below the Alps region. Perhaps the most famous incidence of any disease was the devastating Black Plague of 8th-14th century Europe that eradicated 25 million people (nearly 25% of the population) and marked the end of the Dark Ages. The third endemic began in 1855 in China and was responsible for millions of deaths.

Y. pestis has the ability to cause disease in rodents, insects and humans. The primary carriers of the pathogen are the Oriental rat flea, Xenopsylla cheopis, and infected rodents. The path of transmission to humans usually involves a flea feeding on an infected rodent and becoming a carrier of infection. Once internalized, the bacteria will continue to reproduce until a large blockage is formed in the midgut of the flea, causing digestion and other gastrointestinal functions to cease. When the flea attempts to feed on humans, the blockage inhibits any blood from entering the stomach cavity; instead, portions of the blockage, often containing 11,000-24,000 bacilli, are regurgitated into the mammalian host.

The Y. pestis can currently be found in every continent in the world with the exception of Australia, though it is particularly endemic in third world countries such as Brazil, India, Peru, Madagascar, Vietnam and China. In the United States, the loci of infection are in New Mexico, Arizona, Colorado, California, Oregon and Nevada. There are approximately 10-15 cases a year in the rural U.S. and 1-3,000 Worldwide. The last urban epidemic in the United States was from 1924-1925 in Los Angeles.

Symptoms:

Symptoms include:

    Severe headache.

  • Shaking.

  • Chills.

  • Fever.

  • Malaise.

  • Abdominal pain.

  • Bleeding into the skin and other organ.

  • Pain the affected regional lymph node.

Diagnosis:

Yersinia pestis expresses an envelope glycoprotein called Fraction 1 (F1) antigen only at temperatures >33°C. Serum antibodies to F1 are measured using passive hemagglutination assays (PHA). High titers of antibody along with correlating symptoms, such as buboes, generally indicate a positive diagnosis. Further testing may include X-rays of the lung to check for presence of pneumonic plague, examination of sputum, and lymph node biopsies.

Treatment:

A short-term inactivated vaccine against Y. pestis has existed since the mid-19th century. Though its efficacy has never been precisely measured, field data does show that it lessens incidence and severity of disease resulting from animal transmission. The vaccine is recommended only for laboratory or field workers working with the pathogen, or persons (e.g. Peace Corps volunteers) residing temporarily in rural areas containing the enzootic plague in both human and animal carriers. Though death rates for untreated cases usually approach 100%, antibiotics can be a very effective treatment against the Y. pestis. In some instances, the vaccine will only ameliorate illness, in which case a rigorous treatment of antibiotics is administered. Y. pestis is very susceptible to streptomycin and chloramphenicol; however, concomitant therapy is highly recommended to avoid shock resulting from the lyses of high numbers of Gram-negative cells and the induction of a severe inflammatory response.

Current research on Y. pestis is focused on the identification of genes responsible for transferring infection from fleas to humans, as well as the disease-causing proteins genes that allow bacterial colonization and infection in the lungs. Work is also being done to develop a fully effective vaccine against Y. pestis and more powerful antibiotic treatments to treat this deadly infectious disease.

NOTE: The above information is educational purpose. The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition.

DISCLAIMER: This information should not substitute for seeking responsible, professional medical care.

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