Endemic typhus, also known as murine typhus or flea-borne typhus, is an acute infectious disease transmitted by rat fleas. Its clinical characteristics are similar to that of epidemic typhus, and mild symptoms and short duration are present.
The pathogen of endemic typhus is rickettsia mooseri, also known as rickettsia typhi, and its morphology, staining characteristics, biochemical reactions, culture conditions, and resistance to heat and disinfectants are similar to those of rickettsia prowazekii.
Rickettsia mooseri and rickettsia prowazekii have group-specific heat-resistant soluble antigens in common, so they can have a cross-immunity reaction. They have different particulate antigens, so the disease can be differentiated from epidemic typhus by agglutination test, complement binding test, and immunofluorescence test. Rickettsia mooseri is parasitic in the intestinal wall cells of rat fleas and does not affect the life of the rat fleas, whereas rickettsia prowazekii can cause death of the infected lice.
Source of infection
House rats such as brown rats and yellow-breasted rats are the main source of infection of the disease, and the cycle is rats-rat fleas-rats. Most rats do not die after infection, and rat fleas only suck human blood to infect humans after infected rats die. Patients may also be a source of infection. Rickettsia mooseri can be transmitted via flea eggs. More importantly, domestic cats can carry rickettsia mooseri and transmit to humans. The diversification of infection sources has brought new difficulties to prevention and control.
Modes of transmission
When a rat flea sucks blood of an infected rat, the pathogens in the blood enter the intestine of the flea, but the flea does not die after infection, and the pathogens can replicate in the flea for a long time. When infected flea sucks human blood, it also discharges feces and vomitus containing pathogens on the skin of humans. Rickettsia can enter the body through the breached skin. If the flea is crushed, the pathogens in the flea body can also enter human body through the breach of skin. Diets contaminated with feces of infected rats may cause the disease. The pathogens in dried feces of infected fleas can become aerosols, which can infect humans through the respiratory tract or conjunctiva. Arthropods such as mites and ticks can also carry pathogens and become possible vectors.
Humans are generally susceptible to the disease.
The pathogenesis is basically similar to that of epidemic typhus, but the vascular lesions are milder, and thrombosis in small blood vessels and capillary vessels are less common.
Signs and Symptoms
The incubation period is 6 - 16 days, mostly 12 days.
Rapid onset is present, and some patients may have prodromal symptoms such as fatigue, anorexia, and headaches for 1 - 2 days.
Continuous fever and remittent fever, up to 38 - 40 °C, accompanied by significant headaches, generalized soreness, arthralgia, and conjunctival congestion are present. The duration of fever is generally 9 - 14 days, up to 20 days. Eventually, fever drops gradually.
About 60% - 80% of patients have skin lesions, which usually occur 4 - 7 days after infection. Skin lesions are initially in the chest and abdomen, extending throughout the body within 24 hours, mostly in torso and limbs, rarely in face, neck, soles, and palms. Most skin lesions are irregular, pinhead sized, congestive, maculopapular rashes, and the color often turns from bright red to dark red. Petechial hemorrhages can be seen in few patients. Skin lesions subside in several days, leaving no traces.
Symptoms of the central nervous system are mild, only headaches are present in most patients, and there are few disturbances of consciousness and meningeal irritation.
Other symptoms include cough, nausea, vomiting, diarrhea, mild jaundice, and splenomegaly. Complications are mainly bronchitis and occasionally bronchial pneumonia.
Diagnostic considerations include:
- Rats in the living or working environment, or residence in the epidemic area
- Mild clinical manifestations such as fever and rashes similar to those of epidemic typhus
- Positive serological tests
Chloramphenicol and tetracyclines have specific effects on this disease. Due to adverse effects in clinical practices, chloramphenicol is no longer preferred. Doxycycline is used more frequently, with simple administration, few side effects, and satisfactory results. Erythromycin, fluoroquinolones such as norfloxacin, enoxacin, and ciprofloxacin, and minocycline can also be selected.
The prognosis of this disease is mostly good, and patients usually recover 1 week after onset. However, elderly patients or untreated patients may have a long recovery period. In epidemic outbreaks, only few severe patients die of multiple organ dysfunction syndrome.
Rats and fleas should be eliminated. The disease is usually sporadic, so vaccinations are unnecessary.