Plague

PLAGUE

Synonyms

  • Black death, Pestilential fever, Buboes

Type of zoonosis

  • Metacyclic zoonosis type I

Definition

  • Plague is a severe and highly fatal metazoonosis caused by Yersinia pestis maintained in nature by rodent-flea cycle. It is characterized by acute onset of high fever, painful enlargement of lymph nodes, suppurative periglandular edema (buboes), septicemia and pneumonia. Plague is also called as "black death" because disseminated intravascular coagulation takes place and areas of skin undergo necrosis.

Brief history

  • The second pandemic of plague, known then as the "Black Death", originated in Mesopotamia about the middle of the 11th century, attained its peak in the 14th century and did not disappear until the close of the 17th century. It is thought that the Crusaders, returning from the Holy Land in the 12th and 13th centuries, were instrumental in hastening the spread of the disease. Again the land along trade routes was primarily involved and from them the infections spread east, west and north. During the course of the disease, 25,000,000 people perished, a fourth of the population of the world.
  • "Black death" inspired one of the most enduring nursery rhymes in the English language, “Ring a Ring O'Roses, a pocket full of posies / Ashes, ashes (or ah-tishoo ah-tishoo), we all fall down”.
  • The miasmatic theory of disease described that diseases such as cholera or the Black plague were caused by a miasma (Greek language: "pollution"), a noxious form of "bad air". A remnant of this theory is the name of malaria, from Italian mala aria ("bad air").

Etiology

  • Yersinia pestis. Gram negative, coccobacillus belonging to the Enterobacteriaceae. It looks like "safety pin" (i.e. bipolar) with methylene blue stain or Giemsa's stain or Wayson's stain.
  • It may remain viable for weeks at room temperature in sputum and faeces of fleas.
  • Pathogenicity is determined by the following factors:
    • Fractions (F1), V, W, endotoxin and exodoxin (cardiotoxin).
    • F1 is a capsular heat labile protein, used in serological tests.
    • F1, V and W fractions render Y.pestis resistant to phagocytosis.
    • Cardiotoxin is lethal to mice and rats.

Reservoir and incidence

  • Domestic rats (Rattus rattus) are the most important reservoirs worldwide and the urban rat (Rattus norvegicus).
  • Infected rat fleas (Xenopsylla cheopis) or rodents harbor Yersinia.
  • Fleas may remain infected for months.
  • The disease is also associated with cats, goats, camels, rabbits, dogs and coyotes. Dogs and cats may serve as passive transporters of infected rodent fleas into the home or laboratory.
  • A protein secreted by the Yersinia pestis is a coagulase that causes blood ingested by the flea to clot in the proventriculus. The condition is called as "Blocked flea condition".The bacillus proliferates in the proventriculus, and thousands of organisms are regurgitated by obstructed fleas and inoculated intradermally into the skin.
  • Coagulase is inactive at high temperatures and is thought to explain the cessation of plague transmission during very hot weather.

Transmission

  • Yersinia pestis may enter in to the body through skin, conjunctiva, oral route and inhalation route.  
  • Contact with infected rat fleas (Xenopsylla cheopis) or rodents.
  • Pulmonary form spread by airborne or droplet infection.
  • Human infections from non-rodent species usually result from direct contact with infected tissues, by scratch or bite injuries and handling of infected animals.
  • Man to man transmission is mainly air-borne. 

Disease in animals

  • Self-limiting illness in dogs, and severe, often fatal infection in cats, with fever, lymphadenopathy, haemorrhagic pneumonia and encephalitis.
  • Rodents may carry the disease asymptomatically or develop fatal disease.
  • Fatal infection in rats and squirrels.

Disease in man

  • Bubonic plague
    • Incubation period ranges from few hours to 12 days, generally 2 to 7 days after flea bite.
    • It is the most common form causing fever and swollen, tender lymph nodes, called "Buboes".
    • Rigor and fever are prominent signs.
    • The pain in abdomen often emanates from groin (inguinal buboes) and accompanied with vomiting and diarrhoea, which may be bloody.
    • The bubo is a tender enlarged lymph nodes ranging from 1 to 2 cm. Buboes are extremely tender and the overlying skin is erythematous. It is more common at inguinal, groin and axial region.
  • Systemic plague / Septicemic plague
    • The bubonic form spreads into the blood, it may cause death in 2 days, even before other symptoms of bubonic or pneumonic plague appear.
    • Chills, rapid pulse, fever, severe headache, vomiting and delirium may be manifested. 
  • Pneumonic plague
    • The incubation period varies between 3 to 5 days.
    • It is a systemic plague with lung involvement.
    • Symptoms begin abruptly 2 to 3 days after exposure to the bacteria, which include high fever, chills and often severe headache. A cough develops in 24 hours.
    • The sputum is clear at first, but rapidly becomes flecked with blood, and then becomes uniformly pink or bright red and foamy.
    • The sign of rapid progressive pneumonia, but no pleurisy.
    • Death occurs in 2 days. Mortality may exceed 50%.
    • As a complication, meningitis may be observed in some cases.
  • Pestis minor
    • It is a mild form of plague that usually occurs only in geographic area where the disease is endemic.
    • Symptoms are swollen lymph nodes, fever, headache and exhaustion, which subside within a week.
  • Plague is also called the "black death" because disseminated intravascular coagulation takes place and areas of skin undergo necrosis.

Diagnosis

  • Impression smears of aspirates from buboes or blood or sputum stained with Gram's stain or Giemsa's stain. Organisms have a typical "safety pin" appearance.
  • Culture and identification (confirmation by FAT).
  • Serology: CIE, ELISA, CFT, PHA, Dot-ELISA and FAT.
  • Paired sera may be useful for serological diagnosis of plague.
  • Molecular diagnosis by PCR.

Treatment

  • Streptomycin with tetracycline or chloramphenicol are effective.
  • In acute cases, streptomycin and tetracycline may be used concurrently. Streptomycin can be discontinued once the patient as become afebrile and tetracycline may be continued for 3 to 4 days.
  • In less severe cases, tetracycline alone may be given parentrally or orally.
  • Streptomycin @ 7.5 to 15 mg/kg body weight, i/m at 12 hrs interval and tetracycline @ 5 to 10 mg/kg body weight, i/v at 6 hrs interval. 

Prevention and control

  • Rodent control (using rodenticides like warfarin, zinc phosphate, carbon disulphide, SO2, methyl bromide).
  • Elimination of fleas.
  • Sentinel animal programmes should be used in endemic areas.
  • Masks, gowns and gloves should be worn when handling cats suspected to be infected.
  • Disinfection of all contaminated surfaces with sputum, discharges and dead rats by sanitation
    • Proper disposal of garbage
    • Proper storage of food grains
  • Combined vector and rodent control.
  • Chemoprophylaxis of individuals at high risk. Tetracycline (250 mg) or trimethoprim-sulfamethoxazole may be helpful.
  • Vaccination: Two doses of formalin killed whole bacteria vaccine are given at interval of 7 to 14 days. Immunity starts one week after vaccination and confers immunity for 6 months.
  • Isolation of plague affected people must be done.
Last modified: Friday, 16 September 2011, 9:39 AM