Murine typhus

Murine typhus
Other names: Endemic typhus, flea-borne typhus
Chest X-ray of a 40 yr old with acute respiratory distress syndrome as a complication of murine typhus
Specialty	Infectious disease
Symptoms	Fever, muscle pain, nausea, vomiting, rash[1]
Complications	Bronchiolitis, pneumonia, meningitis, septic shock[2][3]
Causes	Rickettsia typhi[1]
Diagnostic method	Blood test[1] PCR, biopsy[4]
Differential diagnosis	Epidemic typhus, scrub typhus, rickettsialpox, African tick typhus[5]
Prevention	Insect repellent[6][7]
Treatment	Doxycycline[1]
Frequency	Fewer than 100 cases reported in US annually.[8][9]

Murine typhus, also known as endemic typhus or flea-borne typhus, is a form of typhus spread by fleas (Xenopsylla cheopis), usually on rats, in contrast to epidemic typhus which is usually spread by lice.^[1][10][11]

It is often under-recognized, confused with viral illnesses. Most people who are infected do not realize that they have been bitten by fleas.^[5]

The historically term "hunger-typhus" was used by British POWs in Germany at the end of World War I when they described conditions in Germany.^[12]

Signs and symptoms

Small, erythematous, confluent macules

Symptoms may resemble those of measles, rubella, or possibly Rocky Mountain spotted fever. These symptoms are likely caused by a vasculitis caused by the rickettsia.Symptoms of endemic typhus include the following:^[1][12][13]

• Headache
• Fever
• Muscle pain
• Joint pain
• Nausea
• Vomiting
• Rash (40–50% - six days after onset of signs)
• Neurological signs (45%)

• Confusion
• Stupor
• Seizures

Causes

It is caused by the bacterium Rickettsia typhi, and is transmitted by the fleas that infest rats. While rat fleas are the most common vectors, cat fleas and mouse fleas are less common modes of transmission. These fleas are not affected by the infection. Human infection occurs because of flea-fecal contamination of the bites on human skin. Rats, cats, maintain the rickettsia colonization by providing it with a host for its entire life cycle. Rats can develop the infection, and spread the infection to other fleas that infect them, and help multiply the number of infected fleas that can then infect humans.^[14][15][16]

Less often, endemic typhus is caused by Rickettsia felis and transmitted by fleas carried by opossums.^[4]

• 
  Rattus norvegicus
• 
  Rickettsia typhi bacteria
• 
  Common flea can carry Rickettsia felis bacteria

Mechanism

a,b)Rickettsiae replicate in ECs and induce local inflammatory reactions- Rickettsiae enter ECs by endocytosis and rapidly escape from the endosome, the bacteria replicate free in the cytosol and are released by different mechanisms^[17]

In terms of the mechanism of Murine typhus we find that it shares the same pathophysiology as epidemic typhus(but milder).^[18]

Rickettsia enter endothelial cells of blood vessels, and then begin to spread and cause endothelial cellular expansion which results in multiorgan vasculitis. ^[18]

The aforementioned process can cause thrombosis, and small nodules due to, leukocytes, macrophages . Gangrene may occur due to thrombosis which ultimately affects extremities, nose, ear lobes, because of blood supply issues. This vasculitic process may in the end result in organ failure^[18]

Diagnosis

As of 2014, early diagnosis continued to be based on clinical suspicion, and treatment of the disease is indicated even before laboratory results confirm its presence. Because of the lag between the onset of infection and the appearance of antibodies in a blood test, serologic tests are merely confirmatory and retrospective. ^[19][20]

Weil-Felix agglutination reactions are not sensitive to the disease. Indirect fluorescence antibody assays that are specific to R. typhi antigens are the recommended route for detection and diagnosis: diagnostic titers are present in half of all cases within the first week of infection and in nearly all cases by day-15. The sharing of antigens by rickettsiae means routine serologic evaluation will not distinguish between murine typhus and epidemic typhus. Bacterial cultures are rarely performed because although they are highly accurate for diagnosis, the biohazard risk of generating them is often considered too high.^[19][20]

Treatment

Doxycycline

The disease can be fatal if left untreated, but endemic typhus is highly treatable with antibiotics.^{[1] [21]}

Most people recover fully, but death may occur in the elderly, severely disabled or patients with a depressed immune system.^{[1] [21]}

The most effective antibiotics include tetracycline and chloramphenicol, in United States, CDC recommends doxycycline.^[1][21]

Epidemiology

Historically, thousands of murine typhus cases were reported in the United States every year;^[22][8] however, the disease experienced a sudden decline in incidence in the 1940s with the implementation of pest control programs to remove the flea and rodent reservoirs responsible for rickettsial transmission in urban dwellings.^[22][9] Murine typhus infections in the present are more sporadic and infrequent, with fewer than 100 cases reported in the US annually.^[8][9] Nevertheless, R. typhi is still regarded as a bacterium of considerable public health significance, and outbreaks are commonly reported in the Southern US, Southern Europe, Asia, Africa, and Australia.^[22][8] It is estimated that R. typhi prevalence is actually higher than the measured value, since murine typhus is often underreported and misdiagnosed because of its non-specific and mild clinical presentation.^[8][23] Undiagnosed infections are predicted to outnumber reported cases by 4:1.^[9] A recent study presented a clinical case of a patient that works in the Brazilian Amazon and presented an unspecific febrile illness probably caused by Rickettsia typhi since the patient presented specific antibodies to this bacteria. This shows that the R. typhi, geographical distribution can be wider than expected.^[24]

In the United States of America, murine typhus is found most commonly in southern California,^[25] Texas and Hawaii. In some studies, up to 13% of children were found to have serological evidence of infection.^[26]

• 
  Worldwide distribution of R. typhi in the XXI century
• 
  Southern california

See also

• List of mites associated with cutaneous reactions

References

External links