Rickettsiae are small non-motile, pleomorphic, intra cellular parasites about the size of bacteria which involve humans by an insect vector and an animal reservoir. The arthropid vector may be a louse, flea, tick or larval mite, Rickettsias which are pathogenic for humans are capable of multiplying in not only various species of arthropods but also animals and humans and a cycle which involves the insect vector and animal reservoir is important in maintaining it.
Rickettsiae reside in the alimentary tract of the arthropods and the spread in humans takes place by inoculation of their feces through human skin by irritation and scratching or by inhalation. They enter most mammalian cells, invade and proliferate in the endothelial cells of the blood vessels causing vasculitis
The infection caused by these organisms is generally an acute one.
Rickettsiae diseases are worldwide though some are localized to certain regions. The common rickettsial diseases include:
1. Typhus group: Endemic (murine), epidemic, scrub, Brill-Zinsser disease.
2. Spotted fever group: Rocky Mountain spotted fever, tick-borne typhus (Boutonneuse fever, SÃO Paulo Rural, Queensland Tick, North Asian tick-borne rickettsiosis, Rickettsial Pox).
3. Other Rickettsiae diseases: Q and trench fever.
Epidemic typhus (louse-borne)
It is an acute febrile illness caused by R. prowaiekii and is transmitted to humans by body louse either through their bites or by inoculation of their excreta when rubbed into the broken skin.
The lice pass directly to the humans or by infected garments and beddings: Their eggs contain the infective agent and their dried feces may remain infective for many months and may cause infection by inhalation of dust. It occurs mainly in crowded dirty places like jails and institutions where there are verminous persons. Famines and wars are the times when this typhus occurs.
Besides man, flying squirrel, can also serve as potential host to initiate an outbreak provided human vector, the body louse is present.
The incubation period is about 12 days ranging from 7 to 21 days. It is characterized by abrupt onset of high temperature along with headache, body aches, giddiness, chills and vomiting. There are distressing symptoms of headache, malaise and prostration.
Patient is restless, irritable. There is dry coated tongue with photo-phobia as well as flushed face. Fever and prostration remain unabated till on the fifth day a rash appear in the axila, shoulders extending to the abdomen, chest and back.
It is a maculo papular rash which initially is pink (Rose spots) turning into dusky red and later on becomes fixed, confluent and petechial. Purpuric patches may form over pressure points. If the rash is profuse it is an indication of a severe attack. Interestingly face is not effected due to rash and it rarely appear on palms and soles.
At the end of first week, Rickettsiae patient has neurologic features like headache, agitation delirium progressing to stupor and coma. Circulatory disturbances consisting of hypo-tension, tachycardia, Feeble cardiac impulse, shallow breathing, oliguria or anuria and cyanosis develop.
Other features include pneumonitis myocarditis, peripheral gangrene and progressive renal failure. The clinical picture of typhus may vary horn extreme mildness to fulminatingly severe.
In severe forms there is maniacal delirium Meningitis and death may occur. In favorable cases, the symptoms are mild and by end of 2nd week, recovery starts taking place though it is slow. Death is due to circulatory or renal failure.
Diagnosis is by Weil-Felix reaction (OX-19) where a rising agglutination titre (1: 200) is significant. The agglutination may become negative by third or fourth week.
Treatment of Rickettsiae
Chloramphenicol 50 mg/kg or tetracycline 25 mg/kg as initial loading dose and then in divided doses every 6 hourly. In very ill patient corticosteroids are required to reduce toxemia (Prednisolone 60 mg/day in divided doses).
Antibiotics have to be continued for 24-48 hours after patient become afebrile. Besides drugs supportive therapy should be given and patients hydration and electrolyte balance be taken care of.