R. typhi is the causative agent of endemic or murine typhus.
The morphology, cultural characteristics, and pathogenesis of the disease caused by R. typhi are similar to that caused by R. prowazekii. Infection with R. typhi can confer immunity tosubsequent infection.
The typhus fever caused by R. typhi is a milder disease than the epidemic typhus and has a shorter duration. The incubation period varies from 7 to 14 days. The condition has a sudden onset of symptoms with fever, headache, malaise, and myalgia. A rash develops on third to fifth day of infection in approximately the infected patients. The rash is typically present on the chest and abdomen but may spread to palms and soles.Untreated course of the disease may last up to 3 weeks.The endemic typhus differs from epidemic in being a mild illness of shorter duration, associated with few complications and case fatality rate less than 1%.
The murine typhus occurs in many parts of the world par-ticularly in subtropical temperate coastal areas. The condi-tion occurs mainly in sporadic forms. Rats (Rattus rattus), mice, and cats are the natural reservoirs of infection. Humans are the accidental hosts. Rat flea (Xenopsylla cheopis) or cat flea (Ctenocephalides felis) are the main vectors responsible for the transmission of disease. Endemic or flea-borne murine typhus is transmitted from rats to rats by a rat flea and accidentally to humans by the feces of infected fleas. Fleas become infected by feeding on the mice, cat, or other natural host. These infected fleas may subsequently transmit the disease to humans during act of biting. During bite, they transmit the disease by direct inoculation or indirect inoculation of the infected feces into the site of the bite. The cat flea C. felis may also transmit the disease. The infection can also be transmitted by inoculation or inhalation of aerosolized infectious specimens. The infection may also be transmitted by ingestion and food contaminated with infected rat urine or flea feces.
Weil–Felix test used for diagnosis of epidemic typhus is also used for the diagnosis of endemic typhus. IFA test using R.typhi-specific antigen is used as a specific test for serodiagnosisof endemic typhus. A single titer of 1:128 or a fourfold rise in antibody titer in paired sera is diagnostic of the disease. R. typhi is differentiated from R. prowazekii by Neil Mooser reaction and by partial DNA homology.
Tetracycline, doxycycline, and chloramphenicol are highly effective in the treatment of endemic typhus.
Control of endemic typhus is difficult because the fleas caus-ing the disease are distributed widely. The control measures are essentially based on the control of rodent population and flea population in the area endemic for disease.