Epidemic Typhus

 

Rickettsia prowazekii.

PKGhatak,MD

Rickettsia genera have many pathogenic species and out of them, Rickettsia prowazekii is the deadliest for humans. During WWI, a score of soldiers fought and died in the trenches and another score died in the field hospitals because the soldiers were infested by a parasite, body lice loaded with R. prowazekii.

The US army developed a vaccine, using inactivated R. prowazekii, that saved many solders on the US side, but the vaccine was abandoned because of toxicity. No new or effective vaccine is produced since then.

The disease is known as Epidemic Typhus. Typhus means hazy – the term aptly describes the mental conditions of the soldiers. There are two other forms of the same illness are present, and fortunately, both of them produce milder symptoms and fewer fatalities, The initial infection is followed by several months or years of normal health then R. prowazekii, which had remained dormant in the lymphatic tissue, reemerge and produce illness. The disease is called Brill Zinsser Disease. In the southern states of the USA, flying squirrels are harbors of R. prowazekii and humans are accidental victims.

Body lice are infected by sucking patients blood. R. prowazekii multiplies in the gut of the louse and then bursts open. The bacteria remain alive in the dead lice and in the feces of lice. As patients itch, the bite sites get smeared with the bacteria. Dried feces along with the bacteria can float in the air and infect people as they inhale the contaminated air. This characteristic of R. prowazekii leads to certain countries to use these bacteria as a terrorist weapon. Consequently, the US government prohibited the culture of R. prowazekii in laboratories. Only in government facilities, under strict conditions, culture are permitted.

The incubation period is 10 to 14 days. The skin bite sites and the local lymph nodes may become tender. Sudden fever, conjunctivitis, headaches and mental confusion are usual initial symptoms. Deafness due to the 8th cranial nerve lesion, macular skin rashes which spread centrifugally from the axilla but spare the palms and soles and later become confluent and hemorrhagic, and enlarged spleen are characteristic features.

The pathology of the Epidemic typhus is vasculitis. This results in multiorgan infection. Renal failure, pneumonia, myocarditis, gangrene of extremities, encephalitis, and death.

In epidemics the diagnosis is based on clinical grounds and treatment is started immediately without waiting for any laboratory test results. The choice of antibiotic is Doxycycline but Chloramphenicol or Riphampine can be used as a substitute in special circumstances.

In Brill Zinsser disease, the presence of serum IgG antibodies are common. In Endemic typhus, IgM antibodies appear in the blood in 5 to 12 days. The PCR test is rarely used, because as of now, 7 different genotypes are in circulation.

The mortality is 10%. Morbidity is significant, with most having an amputation or organ impairment.

Recent endemics:

Isolated Epidemic Typhus occurs in Siberia, But Russia experienced a local outbreak of Epidemic Typhus. Peru and Burundi also had Epidemic Typhus recently. The endemic areas of Epidemic Typhus are Central and Northeast Africa, central and South America

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