Typhus refers to a group of infectious diseases that are caused by rickettsial organisms and that result in an acute febrile illness. Arthropod vectors transmit the etiologic agents to humans. The principle diseases of this group are epidemic or louse-borne typhus and its recrudescent form known as Brill-Zinsser disease, murine typhus, and scrub typhus. (For more information on pediatric scrub typhus, see the Medscape Reference article Pediatric Scrub Typhus in the Pediatric: General Medicine volume.)
Epidemic typhus is the prototypical infection of the typhus group of diseases, and the pathophysiology of this illness is representative of the entire category. The arthropod vector of epidemic typhus is the body louse (Pediculus corporis). This is the only vector of the typhus group in which humans are the usual host. Rickettsia prowazekii, which is the etiologic agent of typhus, lives in the alimentary tract of the louse. A Rickettsia- harboring louse bites a human to engage in a blood meal and causes a pruritic reaction on the host's skin. The louse defecates as it eats; when the host scratches the site, the lice are crushed, and the Rickettsia- laden excrement is inoculated into the bite wound. The Rickettsia travel to the bloodstream and rickettsemia develops.
R prowazekii is also thought to be transmitted by fleas associated with flying squirrels and their nesting material, by inhaling dried louse feces, or by rubbing Rickettsia -containing louse feces inadvertently into eyes, mucous membranes, or in insect bite–associated wounds.
Rickettsia parasitize the endothelial cells of the small venous, arterial, and capillary vessels. The organisms proliferate and cause endothelial cellular enlargement with resultant multiorgan vasculitis. This process may cause thrombosis, and the deposition of leukocytes, macrophages, and platelets may result in small nodules. Thrombosis of supplying blood vessels may cause gangrene of the distal portions of the extremities, nose, ear lobes, and genitalia. This vasculitic process may also result in loss of intravascular colloid with subsequent hypovolemia and decreased tissue perfusion and, possibly, organ failure. Loss of electrolytes is common.
Some people with a history of typhus may develop a recrudescent type of typhus known as Brill-Zinsser disease. After a patient with typhus is treated with antibiotics and the disease appears to be cured, Rickettsia may linger in the body tissues. Months, years, or even decades after treatment, organisms may reemerge and cause a recurrence of typhus. How the Rickettsia organisms linger silently in a person and by what mechanism recrudescence is mediated are unknown. The presentation of Brill-Zinsser disease is less severe than epidemic typhus, and the associated mortality rate is much lower. Risk factors that may predispose to recrudescent typhus include improper or incomplete antibiotic therapy and malnutrition.
Murine typhus and scrub typhus share the same pathophysiology as epidemic typhus, although they are somewhat milder. The incubation period is approximately 12 days for the typhus group. Prior infection with Rickettsia typhi provides subsequent and long-lasting immunity to reinfection.
Sporadic cases of active infection with R prowazekii, the etiologic agent of epidemic typhus, have been reported. These occurred in the central and eastern portions of the United States and have been linked with exposure to flying squirrels (Glaucomys volans). The flying squirrel acts as the host for R prowazekii, and transmission to humans is believed to occur via squirrel fleas or lice. Murine typhus caused by infection with Rickettsia felis is associated with opossums, cats, and their fleas and occurs in southern California and southern Texas. Most cases of murine typhus in Texas occur in spring and summer, whereas, in California, the illness is most common in the summer and fall.
In 2013, 12 patients with murine typhus were identified in Galveston, Texas, which may reflect a re-emergence of R typhi in the rat population and/or a cycle involving opossums and cats with R felis. Murine typhus is most common in adults, but infection may occur in any age group. No indigenous cases of scrub typhus have occurred in the United States, although infections have been diagnosed in patients returning from endemic areas.
Epidemic typhus occurs in Central and South America, Africa, northern China, and certain regions of the Himalayas. Outbreaks may occur when conditions arise that favor the propagation and transmission of lice. Brill-Zinsser disease develops in approximately 15% of people with a history of primary epidemic typhus.
Murine typhus occurs in most parts of the world, particularly in subtropical and temperate coastal regions. Murine typhus occurs mainly in sporadic cases, and incidence is probably greatly underestimated in the more endemic regions. Rats, mice, and cats, which are hosts for the disease, are particularly common along coastal port regions. Populations of the flea vector may rise during the summer months in temperate climates, subsequently increasing the incidence of murine typhus. The homeless are particularly vulnerable. Prior infection with R typhi provides immunity to subsequent reinfection.
Scrub typhus occurs in the western Pacific region, northern Australia, and the Indian subcontinent. The incidence of scrub typhus is largely unknown. Many cases are undiagnosed because of its nonspecific manifestations and the lack of laboratory diagnostic testing in endemic areas. However, one study found that the incidence of scrub typhus in Malaysia was approximately 3% per month, and multiple infections in the same individual are possible because of a lack of cross-immunity among the various strains of its causative organism, Orientia tsutsugamushi.
Epidemic typhus causes the most severe clinical presentation among the typhus group of rickettsial infections. Patients with severe epidemic typhus may develop gangrene, leading to a loss of digits, limbs, or other appendages. The vasculitic of epidemic typhus process may also lead to CNS dysfunction, ranging from dullness of mentation to coma, multiorgan system failure, and death. Untreated epidemic typhus carries a mortality rate of as low as 20% in otherwise healthy individuals and as high as 60% in elderly or debilitated persons. Since the advent of widely available antibiotic treatment, the mortality rates associated with epidemic typhus have fallen to approximately 3-4%.
The mortality rate among treated patients with murine typhus is 1-4% and less than 1% for scrub typhus.
GeoSentinel, a global network that monitors travel-related morbidity, reported no fatalities in 16 cases of murine typhus and 13 cases of scrub typhus that occurred in international travellers from 1996-2011.
The typhus group of infections has no sexual predilection.
The typhus group of infections has no age predilection. However, in the United States, murine typhus and sporadic cases of epidemic typhus have mainly occurred in adults.
Patients with typhus may have a history that includes the following:
The duration of most clinical symptoms and signs in untreated typhus is approximately 2 weeks. Several months may pass before complete recovery from fatigue and malaise.
Epidemic typhus is the prototypical infection of the typhus group. As described in the Pathophysiology section, typhus is a multisystem vasculitis and may cause a wide array of clinical manifestations, as follows:
Scrub typhus may be difficult to recognize and diagnose because the symptoms and signs of the illness are often nonspecific.
Fever rises to 39-41ºC and is persistent in patients with untreated typhus.
Patients with typhus have relative bradycardia with the fever.
Fever may persist for 24-72 hours after initiation of antibiotic therapy.
This is most common in scrub typhus because of frequent pulmonary involvement.
The macular, maculopapular, or petechial rash initially occurs on the trunk and axilla and spreads to involve the rest of the body except for the face, palms, and soles.
Rash may be petechial in patients with epidemic or murine typhus.
This occurs in scrub typhus in the region of the arthropod bite and inoculation. Generalized lymphadenopathy may follow.
Lymph nodes are often tender and enlarged.
Generalized lymphadenopathy may occur.
This is found in the scrub form of typhus and is essential in confirming a clinical diagnosis. It occurs in up to 60% of cases.
Eschar occurs at the site of the arthropod bite. It starts as a painless papule, and the lesion becomes indurated and enlarged. The center of the lesion becomes necrotic and develops into a black scab.
Mild splenomegaly may occur.
Mild hepatomegaly may occur.
Conjunctival suffusion may occur in scrub typhus.
Typhus is an acute febrile illness caused by rickettsial organisms. Rickettsia are pleomorphic bacteria that may appear as cocci or bacilli and are obligate intracellular parasites.
Epidemic typhus is caused by the bacterium R prowazekii, and the vector is the body louse.
P corporis is the most common louse vector; however, Pediculus capitis and Phthirus pubis also transmit epidemic typhus.
Humans are the host in epidemic typhus, but the flying squirrel has also been linked with the disease in several cases in the United States.
The louse becomes infected with R prowazekii after feeding on a rickettsemic person with a primary case of typhus or during a recrudescent case (Brill-Zinsser disease).
Of all the typhus vectors, the louse is the only arthropod that dies of this infection. Rickettsia live in the alimentary tract and cause obstruction and subsequent death of the louse after 2-3 weeks of infection.
All arthropod vectors cause inoculation of Rickettsia into the host by the same mechanism described above (see Pathophysiology).
Murine typhus is caused by R typhi, and the vector is the rat or cat flea (Xenopsylla cheopis, Ctenocephalides felis).
Rats (Rattus rattus), mice, and cats are the usual hosts; human infection is accidental.
Fleas become infected after engaging in a blood meal of a rickettsemic host; however, the fleas are not affected by the bacteria as are the lice in epidemic typhus.
Infected fleas may subsequently cause disease by direct inoculation or by indirect inoculation of the infected feces into the site of the bite wound.
Aerosolization of the feces and inoculation into the respiratory tract or into a mucous membrane are other possible routes of infection.
Scrub typhus is caused by O tsutsugamushi (formerly Rickettsia tsutsugamushi) via the mite Leptotrombidium akamushi and possibly Leptotrombidium deliense.
The life cycle of the mite involves 4 stages of development, but only the larval stage (chigger) requires a blood meal and is infectious to humans and other mammals.
Once the mite is infected, it acts as a reservoir for Rickettsia.
The infection is maintained in mites from generation to generation by transovarial transmission.
Humans are accidental hosts in scrub typhus; rats, mice, and larger mammals are the usual hosts.
Laboratory studies are not particularly helpful in confirming a diagnosis of typhus. These studies assist the clinician in assessing the degree of severity of the illness and in helping exclude other diseases in the differential diagnoses.
The diagnosis of typhus is clinically suggested when the appropriate historical elements are elicited from a patient who presents with the characteristic symptoms and signs.
Antibiotic therapy should begin promptly when the diagnosis is suspected; thereafter, appropriate laboratory studies can be serially performed as needed.
Diagnosis may be confirmed using laboratory tests; however, more than one week may pass before patients mount a demonstrable immune response that can be measured serologically.
Laboratory confirmation of typhus is obtained irrespective of the clinical presentation.
Typhus is a vasculitic process that is capable of causing various abnormal laboratory values. Any organ may be affected, and multiorgan system dysfunction or failure may occur if the illness is not diagnosed and treated in the early stages. These abnormalities, listed by organ system, may include the following:
Indirect immunofluorescence assay (IFA) or enzyme immunoassay (EIA) testing can be used to evaluate for a rise in the immunoglobulin M (IgM) antibody titer, which indicates an acute primary disease.
Brill-Zinsser disease can be confirmed in a patient with a history of primary epidemic typhus who has recurrent symptoms and signs of typhus and a rise in the immunoglobulin G (IgG) antibody titer, which indicates a secondary immune response.
IFA and EIA tests can be used to confirm a diagnosis of typhus, but they do not identify the various rickettsial species.
Polymerase chain reaction (PCR) amplification of rickettsial DNA of serum or skin biopsy specimens can be used for diagnosing typhus.
The complement fixation (CF) test is a serological test that can be used to demonstrate which specific rickettsial organism is causing disease by detection of specific antibodies.
Rapid diagnostic assays for scrub typhus, such as latex agglutination tests, are currently under development.
No imaging studies are specifically indicated to aid in diagnosing typhus. Imaging studies are indicated only on a case-by-case basis to evaluate potential complications or as needed.
Chest radiography may be a complementary tool to evaluate the clinical course of scrub typhus. Chest radiographic examinations should be obtained during the first week after the onset of illness.
Rickettsia may be observed in tissue sections using Giemsa or Gimenez staining techniques.
Antibiotics are the standard of care in the treatment of typhus. Continue antibiotics for 48-72 hours after the fever has resolved. A second course of antibiotic therapy is usually curative in cases of recrudescent typhus.
Other supportive measures may be used as necessary.
Activity is as tolerated.
The goals of pharmacotherapy are to reduce morbidity, to prevent complications, and to eradicate infection.
Clinical Context: Inhibits protein synthesis and thus bacterial growth by binding to 30S and possibly 50S ribosomal subunits of susceptible bacteria. No dose adjustment is necessary in renal impairment.
Clinical Context: Generally bacteriostatic to most susceptible microorganisms; binds to the 50S bacterial ribosomal subunits and inhibits bacterial growth by inhibiting protein synthesis. Not preferred therapy for treating patients with typhus.
Specific antimicrobial therapy effective against rickettsia should be used. Doxycycline and chloramphenicol are used as antirickettsial agents for the treatment of typhus.
In Thailand, the emergence of doxycycline-resistant scrub typhus has caused clinicians to seek alternative antimicrobials. Azithromycin and rifampicin have been shown to be effective in small trials conducted in areas with known doxycycline resistance.
Inpatient care may be required for ill patients with typhus who cannot maintain adequate oral hydration/intake or enteral antibiotic therapy.
Patients with complications from typhus may need inpatient care for further diagnosis, evaluation, and management for these disorders (see Complications).
Decisions regarding the need for inpatient care should be assessed on a case-by-case basis.
No further outpatient care is usually necessary in uncomplicated cases of typhus.
Avoid exposure to areas known to be endemic for typhus.
Insecticides may be helpful in controlling the arthropod vectors that spread typhus.
Reduce the rodent host population.
Wear protective clothing (eg, long-sleeved shirts, long pants) in endemic areas.
Practice good personal hygiene, including frequent bathing and frequent changing of clothes.
Vaccination for typhus is not recommended, and manufacturing of the vaccine has been discontinued in the United States.
Signs, symptoms, and potential complications of typhus are due to hematogenous spread of organisms with resultant endothelial proliferation and vasculitis.
The central nervous, musculoskeletal, and cardiovascular systems may be involved, as well as the skin, lungs, and kidneys. Multiorgan system involvement is possible.
Vasculitis may result in hypovolemia, electrolyte disturbances, and digital gangrene.
Hemodynamic status and fluid/electrolyte replacement should be diligently monitored.
Secondary infections, such as bacterial pneumonia, should be treated appropriately.
aUncomplicated cases of typhus that are diagnosed promptly and antibiotic therapy initiated early generally carry an excellent prognosis. Mortality rates are greatly reduced when appropriate antibiotics are initiated promptly (see Mortality/Morbidity).
Complicated cases of typhus generally carry a good prognosis, but this varies depending on the severity of the specific complications and the health status of the patient at the time of disease onset.