Epidemic typhus is the most severe form of rickettsial infections. This louse-borne typhus is an acute febrile illness that features a headache, rash, myalgia, vasculitis, and is complicated by severe central nervous system (CNS) manifestations, gangrene, and high rates of death in untreated individuals. It is diagnosed by a thorough history and evaluation of risk factors, clinical exam, and laboratory studies.
Epidemic typhus (ET) is caused by Rickettsia prowazekii, which is transmitted by human body louse  . As a part of the typhus group, it is described as an acute febrile illness. Significant outbreaks have occurred during the Napoleonic Wars and World War I and II, resulting in the death of millions  . More recent epidemics emerged in Algeria, Burundi, and Russia   . Regions that have been affected include the parts of Africa, China, the Himalayas, and Central and South America. Risk factors encompass war, natural disaster, overcrowding, poor hygiene, and cold weather. Additionally, military personnel and medical relief workers are considered vulnerable populations.
The clinical presentation is characterized by nonspecific symptoms such as a high fever, intense headache, myalgia, and a rash . The latter erupts approximately 5 to 7 days after the onset of the disease . Additionally, ET may cause pneumonia, multisystemic vasculitis, and CNS manifestations such as mental status changes, encephalitis or coma. Other features are malaise, rigors, and sudden prostration.
ET can give rise to gangrene infection and the resultant loss of digits, extremities and other body parts. Also, patients may develop hypotension with vascular collapse, renal failure, and other severe sequelae. If left untreated, epidemic typhus leads to death in up to 30% of cases   . Note that nearly 15% of victims develop the Brill-Zinsser disease, which is a recrudescent form that may recur years later.
Findings are notable for a high fever that reaches 39-41ºC and remains elevated if untreated. Also remarkable is the rash, which appears as maculopapular or petechial. It manifests centrally and spreads to the extremities while sparing the face, palms, and soles. Other signs may comprise of splenomegaly and bruises.
During the assessment, the clinician should elicit the risk factors and patient history, and perform a careful physical exam and the appropriate tests. Note the administration of antibiotics should be started as soon as the provisional diagnosis for this diseases is established.
Generally, laboratory studies such as complete blood count (CBC) and comprehensive metabolic panel (CMP) consisting of liver and renal function tests, electrolyte levels, serum albumin concentration, and others should be obtained. Common findings may include but are not limited to leukopenia, leukocytosis, thrombocytopenia, mild increase in transaminases, hyponatremia, hypoalbuminemia, and azotemia.
The diagnostic panel consists of indirect immunofluorescence assay (IFA) and enzyme immunoassay (EIA), which are used to measure immunoglobulin (Ig) M antibodies. Serological testing is not useful in acute cases since the immune response is not demonstrable during this period. Moreover, polymerase chain reaction (PCR) performed on blood or skin biopsy samples suggests Rickettsia and the specific species of this pathogen . Culture is not helpful.
Brill-Zinsser disease is identified in patients with recurrent manifestations and a measurable elevation of IgG titer.
A chest X-ray should be obtained in those with pneumonia .