eMedicine Specialties > Infectious Diseases > Bacterial Infections

Typhus

Author: Jason F Okulicz, MD, Assistant Professor of Medicine, Uniformed Services University of the Health Sciences; Staff, Infectious Disease Service, Brooke Army Medical Center
Coauthor(s): Mark S Rasnake, MD, Assistant Professor of Medicine, Program Director, Internal Medicine Residency, University of Tennessee Graduate School of Medicine; Consulting Staff, Department of Infectious Diseases, University of Tennessee Medical Center at Knoxville; Eric A Hansen, DO, Fellow, Clinical Instructor, Department of Internal Medicine, Division of Infectious Diseases, Winthrop-University Hospital, State University of New York at Stony Brook; Burke A Cunha, MD, Professor of Medicine, State University of New York School of Medicine at Stony Brook; Chief, Infectious Disease Division, Winthrop-University Hospital
Contributor Information and Disclosures

Updated: Sep 18, 2008

Introduction

Background

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 eMedicine article Scrub Typhus in the Pediatric: General Medicine volume.)

Pathophysiology

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.

Frequency

United States

Approximately 15 documented 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).¹ 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,² 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. Murine typhus is most common in adults, but infection may occur in any age group.³ No indigenous cases of scrub typhus have occurred in the United States, although infections have been diagnosed in patients returning from endemic areas.

International

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. 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.⁴

Mortality/Morbidity

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.

Sex

The typhus group of infections has no sexual predilection.

Age

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.

Clinical

History

Patients with typhus may have a history that includes the following:

• Patients may have had exposure to an endemic area
• Occupational exposure: Medical and military personnel are potentially at higher risk for typhus than the general population in endemic areas.
• Overcrowding leads to close personal contact and spread of arthropod vectors (particularly lice) among individuals.
• Lack of personal hygiene: Infrequent bathing and changing of clothes provides a hospitable environment for body lice.
• Appropriate season: Cold weather may lead to overcrowding indoors and infrequent bathing and changing of clothes, which are advantageous for lice. Flea vectors are more abundant in warmer weather, when their hosts are more plentiful.
• Abrupt onset of fever, headache, and rash are common symptoms in rickettsial infections.
• Patients may have a history of flea bite.
• History may include exposure to natural disaster or war.
• Other less common symptoms of typhus include nonproductive cough and deafness/tinnitus.
• 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.
  • Fever is characterized by abrupt onset.
  • Headache is characterized by abrupt onset and is unremitting.
  • A maculopapular/petechial rash occurs on days 4-7 and may begin on the axilla and trunk and spread peripherally. The rash of Rocky Mountain spotted fever (RMSF) typically begins on the extremities and spreads centrally.
  • Other symptoms of typhus may include rigors, myalgias, malaise, and CNS symptoms (ranging from mental dullness to coma).
• Scrub typhus may be difficult to recognize and diagnose because the symptoms and signs of the illness are often nonspecific.
  • A painless papule develops at the site of the chigger bite and subsequently undergoes central necrosis with formation of an eschar.
  • Regional lymphadenopathy, with development of large and tender lymph nodes, occurs at the site of the bite and may lead to generalized lymphadenopathy.
  • The nonspecific presentation and lack of the characteristic eschar in 40% of patients leads to many undiagnosed cases of scrub typhus.

Physical

• Fever
  • 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.
• Tachypnea and cough: This is most common in scrub typhus because of frequent pulmonary involvement.
• Rash
  • 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.
• Regional lymphadenopathy
  • 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
• Eschar
  • 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.
• Other features
  • Mild splenomegaly may occur.
  • Mild hepatomegaly may occur.
  • Conjunctival suffusion may occur in scrub typhus.

Causes

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.¹
  • 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.

• Search for CME/CE on This Topic »

• Scrub Typhus (Dermatology)
• Scrub Typhus (Pediatrics: General Medicine)
• Rickettsial Infection (Pediatrics: General Medicine)
• Boutonneuse Fever (Dermatology)

• Charles-Jules-Henri Nicolle
• Infectious Diseases in International Adoptees From South Korea
• Ethnic Variability in Adiposity and Cardiovascular Risk: The Variable Disease Selection Hypothesis