scrub typhus


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Scrub Typhus

 

Definition

Scrub typhus is an infectious disease that is transmitted to humans from field mice and rats through the bite of mites that live on the animals. The main symptoms of the disease are fever, a wound at the site of the bite, a spotted rash on the trunk, and swelling of the lymph glands.

Description

Scrub typhus is caused by Rickettsia tsutsugamushi, a tiny parasite about the size of bacteria that belongs to the family Rickettsiaceae. Under the microscope, rickettsiae are either rod-like (bacilli) or spherical (cocci) in shape. Because they are intracellular parasites, they can live only within the cells of other animals.
R. tsutsugamushi lives primarily in mites that belong to the species Leptotrombidium (Trombicula) akamushi and Leptotrombidium deliense. In Japan, some cases of scrub typhus have been reportedly transmitted by mites of the species Leptotrombidium scutellare and Leptotrombidium pallidum. The mites have four-stage life cycles: egg, larva, nymph, and adult. The larva is the only stage that can transmit the disease to humans and other vertebrates.
The tiny chiggers (mite larvae) attach themselves to the skin. During the process of obtaining a meal, they may either acquire the infection from the host or transmit the rickettsiae to other mammals or humans. In regions where scrub typhus is a constant threat, a natural cycle of R. tsutsugamushi transmission occurs between mite larvae and small mammals (e.g., field mice and rats). Humans enter a cycle of rickettsial infection only accidentally.
Scrub typhus is also known as tsutsugamushi disease. The name tsutsugamushi is derived from two Japanese words: tsutsuga, meaning something small and dangerous, and mushi, meaning creature. The infection is called scrub typhus because it generally occurs after exposure to areas with secondary (scrub) vegetation. It has recently been found, however, that the disease can also be prevalent in such areas as sandy beaches, mountain deserts, and equatorial rain forests. Therefore, it has been suggested that the names miteborne typhus, or chigger-borne typhus, are more appropriate. Since the disease is limited to eastern and southeastern Asia, India, northern Australia and the adjacent islands, it is also commonly referred to as tropical typhus.
The seasonal occurrence of scrub typhus varies with the climate in different countries. It occurs more frequently during the rainy season. Certain areas such as forest clearings, riverbanks, and grassy regions provide optimal conditions for the infected mites to thrive. These small geographic regions are high-risk areas for humans and have been called scrub-typhus islands.

Causes and symptoms

The incubation period of scrub typhus is about 10 to 12 days after the initial bite. The illness begins rather suddenly with shaking chills, fever, severe headache, infection of the mucous membrane lining the eyes (the conjunctiva), and swelling of the lymph nodes (lymphadenopathy). A wound (lesion) is often seen at the site of the chigger bite. Bite wounds are common in whites but rare in Asians.
The initial lesion, which is about 1 cm (0.4 in) in diameter and flat, eventually becomes elevated and filled with fluid. After it ruptures, it becomes covered with a black scab (eschar). The patient's fever rises during the first week, generally reaching 40-40.5°C (104-105°F). About the fifth day of fever, a red spotted rash develops on the trunk, often extending to the arms and legs. It may either fade away in a few days or may become spotted and elevated (maculopapular) and brightly colored. Cough is present during the first week of the fever. An infection of the lung (pneumonitis) may develop during the second week.
In severe cases, the patient's pulse rate increases and blood pressure drops. The patient may become delirious and lose consciousness. Muscular twitching may develop. Enlargement of the spleen is observed. Inflammation of the heart muscle (interstitial myocarditis) is more common in scrub typhus than in other rickettsial diseases. In untreated patients, high fever may last for more than two weeks. With specific therapy, however, the fever breaks within 36 hours. The patient's recovery is prompt and uneventful.

Diagnosis

Patient history and physical examination

Differentiating scrub typhus from other forms of typhus as well as from fever, typhoid and meningococcal infections is often difficult during the first several days before the initial rash appears. The geographical location of scrub typhus, the initial sore caused by the chigger bite, and the occurrence of specific proteins capable of destroying the organism (antibodies) in the blood, provide helpful clues and are useful in establishing the diagnosis.

Laboratory tests

Diagnostic procedures involving the actual isolation of rickettsiae from the blood or other body tissues are usually expensive, time-consuming, and hazardous to laboratory workers. As a result, several types of tests known as serological (immunological) tests are used widely to confirm the clinical diagnosis in the laboratory.
Specific antibodies develop in the body in response to an infection. The development of antibodies during the recovery period indicates that an immune response is present. The formation of antibodies is the basic principle of a serological test. Three different tests are available to diagnose rickettsial infections. The most widely used is the Weil-Felix test. This test is based on the fact that some of the antibodies that are formed in the body during a rickettsial infection can react with certain strains (OX-2 and OX-19) of Proteus bacteria and cause them to clump (agglutinate). The clumping is easily seen under the microscope. The Weil-Felix test is easy and inexpensive to perform, with the result that it is widely used. The WeilFelix test, however, is not very specific. In addition, the clumping is not detectable until the second week of the illness, which limits the test's usefulness in early diagnosis.
A second test known as a complement fixation (CF) test is based on the principle that if antibodies are formed in the body in response to the illness, then the antigen and the antibody will form complexes. These antigen-antibody complexes have the ability to inactivate, or fix, a protein that is found in blood serum (serum complement). The serum complement fixation can be measured using standardized biochemical tests and confirms the presence of antibodies. A third test known as the fluorescent antibody test uses fluorescent tags that are attached to antibodies for easy detection. This test has been developed using three strains of Rickettsia tsutsugamushi and has proven to be the most specific for diagnosis.

Treatment

Scrub typhus is treated with antibiotics. Chloramphenicol (Chloromycetin, Fenicol) and tetracycline (Achromycin, Tetracyn) are the drugs of choice. They bring about prompt disappearance of the fever and dramatic clinical improvement. If the antibiotic treatment is discontinued too quickly, especially in patients treated within the first few days of the fever, relapses may occur. In patients treated in the second week of illness, the antibiotics may be stopped one to two days after the fever disappears.
Antibiotics are given intravenously to patients too sick to take them by mouth. Patients who are severely ill and whose treatment was delayed may be given corticosteroids in combination with antibiotics for three days.

Prognosis

Before the use of antibiotics, the mortality rate for scrub typhus varied from 1-60%, depending on the geographic area and the rickettsial strain. Recovery also took a long time. With modern treatment methods, however, deaths are rare and the recovery period is short.

Prevention

General precautions

As of early 2004 there are no effective vaccines for scrub typhus. In endemic areas, precautions include wearing protective clothing. Insect repellents containing dibutyl phthalate, benzyl benzoate, diethyl toluamide, and other substances can be applied to the skin and clothing to prevent chigger bites. Clearing of vegetation and chemical treatment of the soil may help to break up the cycle of transmission from chiggers to humans to other chiggers.

Key terms

Agglutinin — An antibody that causes particulate antigens such as bacteria or other cells to clump together.
Endemic area — A geographical region where a particular disease is prevalent.
Eschar — A hard crust or scab. In scrub typhus, an eschar forms over the initial sore from the chigger bite.
Intracellular parasite — An organism which can only feed and live within the cell of a different animal.
Maculopapular rash — A rash characterized by raised, spotted lesions.
Prophylactic dosage — Giving medications to prevent or protect against diseases.
Rickettsia — A rod-shaped infectious microorganism that can reproduce only inside a living cell. Scrub typhus is a rickettsial disease.
Serological tests — Tests of immune function that are performed using the clear yellow liquid part of blood.

Prophylactic antibiotic dosage

It has been shown that a single oral dose of chloramphenicol or tetracycline given every 5 days for a total of 35 days, with 5-day nontreatment intervals, actually produces active immunity to scrub typhus. This procedure is recommended under special circum-stances in certain areas where the disease is endemic.

Resources

Books

Beers, Mark H., MD, and Robert Berkow, MD., editors. "Scrub Typhus." Section 13, Chapter 159 In The Merck Manual of Diagnosis and Therapy. Whitehouse Station, NJ: Merck Research Laboratories, 2004.

Periodicals

Cheng, V. C., A. K. Wu, I. F. Hung, et al. "Clinical Deterioration in Community Acquired Infections Associated with Lymphocyte Upsurge in Immunocompetent Hosts." Scandinavian Journal of Infectious Diseases 36, no. 10 (2004): 743-751.
Ralph, A., M. Raines, P. Whelan, and B. J. Currie. "Scrub Typhus in the Northern Territory: Exceeding the Boundaries of Litchfield National Park." Communicable Diseases Intelligence 28 (February 2004): 267-269.
Takahashi, M., H. Misumi, H. Urakami, et al. "Mite Vectors (Acari: Trombiculidae) of Scrub Typhus in a New Endemic Area in Northern Kyoto, Japan." Journal of Medical Entomology 41 (January 2004): 107-114.

Organizations

Centers for Disease Control and Prevention. 1600 Clifton Rd., NE, Atlanta, GA 30333. (800) 311-3435, (404) 639-3311. http://www.cdc.gov.

tsu·tsu·ga·mu·shi dis·ease

an acute infectious disease, caused by Rickettsia tsutsugamushi and transmitted by the mites Trombicula akamushi and T. deliensis, which occurs in harvesters of hemp in some parts of Southeast Asia including Japan; characterized by fever, painful swelling of the lymphatic glands, a small blackish scab on the genitals, neck, or axilla, and an eruption of large dark red papules.

scrub typhus

n.
An acute infectious disease common in Asia that is caused by the mite-borne bacterium Orientia tsutsugamushi and is characterized by sudden fever, painful swelling of the lymph nodes, and sometimes skin lesions, including an eschar at the site of infection. Also called Japanese river fever, tsutsugamushi disease.

scrub typhus

an acute febrile disease caused by several strains of the species Orientia tsutsugamushi (formerly Rickettsia tsutsugamushi) and transmitted from infected rodents to humans by mites. It is found in Asia, India, northern Australia, and the western Pacific islands. The clinical course ranges from mild to severe and is characterized by a necrotic papule or black eschar at the site of the lesion caused by the bite of the small arachnid. Tender enlarged regional lymph nodes, fever, severe headache, eye pain, muscle aches, and a generalized rash usually occur. In severe cases the myocardium and the central nervous system may be involved. The DNA-PCR and indirect fluorescent antibody tests are useful in diagnosis. Treatment with antibiotics, such as chloramphenicol, doxycycline, or azithromycin, has reduced the mortality rate to nearly zero. Person-to-person transmission is not known to occur. No effective vaccine is available, and second attacks are common because of antigenic differences in various strains of rickettsiae. Prevention includes avoiding mite-infested terrain, reducing the rodent population, destroying scrub vegetation, and using insect repellents. Also called Japanese flood fever, Japanese river fever, mite typhus, tropical typhus, tsutsugamushi disease. Compare Q fever, Rocky Mountain spotted fever, typhus.

scrub typhus

Tsutsugamushi disease, mite-borne typhus, tropical typhus A mite-borne infection by Rickettsia tsutsugamushi Epidemiology ST occurs in Japan, India, Australia Vector Chigger–larval stage of a mite, Leptotrombidium deliensis, or Trombicula pseudo-akamushi, inhabitants of scrub vegetation that feed on host rodents Clinical 1-3 wk incubation with prodromal Sx of headache, malaise, anorexia; scarification of inoculation papule is followed by abrupt onset of high fever with pulse-temperature dissociation, headache, ocular pain, conjunctivitis, malaise, lymphadenopathy and a dark crusted eschar or tache noire at the site of the chigger–mite larva bite, cardiac dysfunction with minor EKG changes–eg, T wave inversion, a pale pink, centrifugal maculopapular rash, lymphadenopathy, interstitial pneumonia Diagnosis Proteus OX-K antigen seropositivity Treatment Tetracycline, chloramphenicol, ciprofloxin Mortality 10-30% if untreated

tsu·tsu·ga·mu·shi dis·ease

(tsū'tsū-gă-mū'shē di-zēz')
An acute infectious disease, caused by Orientia tsutsugamushi and transmitted by Trombicula akamushi and T. deliensis, which occurs in harvesters of hemp in some parts of Japan; characterized by fever, painful swelling of the lymphatic glands, a small, blackish scab (on the genitals, neck, or axilla), and an eruption of large, dark red papules.
Synonym(s): akamushi disease, mite typhus, scrub typhus, tropical typhus.

scrub typhus

An acute infectious disease caused by Rickettsia tsutsugamushi and transmitted to men by the bite of the larval trombiculid mite. The disease is common in rural areas in Asia. There is a black scar at the site of the bite (tache noir), sudden fever, painful swelling of the lymph nodes, headache, eye pain, cough and a skin rash. Antibiotics are effective.

scrub

1. low trees and bushes. Called also browse. Edible enough for livestock to graze them especially when more conventional feed is short. Lopping of this material for feeding is a husbandry practice in some arid zones. Lends itself to indigestion in ruminants because of its indigestibility, especially if it is the main article of diet.
2. to cleanse by vigorous scrubbing with a brush. See also surgical scrub (below).

scrub animal
one from grade parents, non-descript and not showing the predominant characteristics of any breed. Generally applied to agricultural animals.
scrub ironbark
brideliaexalta, B. leichhardtii.
scrub-itch mite
scrub kurrajong
pimeleamicrocephala, P. pauciflora.
scrub-up
see scrub (2).
scrub suit
the outer, protective clothing worn by operating room personnel. Usually specially prepared within the hospital's sterilizing facility to minimize contamination in the surgical suite.
surgical scrub
the ritualistic presurgical preparation of hands and arms by surgeons and their assistants. Includes thorough, vigorous and systematic cleaning with a brush of all skin surfaces. Persons prepared in this manner are then considered 'scrubbed-up', ready to take part in the surgical procedure, and are not allowed to touch any nonsterile surfaces.
scrub tick
see ixodesholocyclus.
scrub typhus
a disease of humans transmitted by Trombicula akamushi and resident in rodents which serve as reservoirs. Called also Japanese river fever, tsutsugamushi disease.

typhus

acute infectious diseases caused by Rickettsia which are usually transmitted from infected rats and other rodents to humans by lice, fleas, ticks and mites.

Abyssinian tick typhus
canine typhus, canine tick typhus
see canine ehrlichiosis.
epidemic typhus
see rickettsiaprowazeki.
Kenya typhus
murine typhus
a disease of humans caused by Rickettsia typhae; rats and cats are the mammalian reservoir.
Queensland tick typhus
caused by Rickettsia australis. See queensland tick typhus.
Sao Paulo typhus
scrub typhus
caused by Orientia tsutsugamushi. Wild rodents and occasionally dogs may be hosts.
References in periodicals archive ?
Spatial distribution analysis of scrub typhus in Korea.
It is increasingly evident that scrub typhus needs to be considered along with enteric fever, malaria, dengue and tuberculosis in the differential diagnosis of all acute febrile illnesses in children irrespective of the symptoms, localizing signs and presence or absence of eschar.
Assessment of the risk of scrub typhus to the US Forces Korea (USFK) population is difficult, as few cases are diagnosed in the USFK population compared to the disease presence in the Korean population (Table 1).
Rapid diagnosis of scrub typhus in rural Thailand using polymerase chain reaction.
Many of the recent reports of scrub typhus and other rickettsial diseases from the Indian sub-continent are based on clinical findings and the relatively nonspecific Weil-Felix test (5) including the study by Kamarasu and co-workers (9).
However, the diagnosis of scrub typhus in patients with ARDS is critical for initiating appropriate and timely doxycycline treatment.
Scrub typhus is an important tropical rickettsial infection.
Interpretation & conclusion: This community based study from south India involving several districts in Tamil Nadu, showed that scrub typhus and rickettsial illnesses were widely distributed in the State.
Given the broad endemicity of scrub typhus in the Asia-Pacific region and variations in clinical manifestations that may be attributable to strain variation, thorough investigation into the regional distribution of genotypes is warranted.
Of the 3 patients, the woman and the boy had other vectorborne infections: scrub typhus, transmitted by Leptotrombidium mites, and P.
To the Editor: Scrub typhus, which is caused by the bacterium Orientia tsutsugamushi, had been considered a disease of the tropical zone in China until the first outbreak in the temperate zone of Shandong Province in 1986 (1).
In 2010 and 2011, nine patients in Shizuoka Prefecture, Japan, who had rickettsiosis-like symptoms, were suspected to have Japanese spotted fever or scrub typhus, but they were serologically negative by IFA.