Typhus is a group of infectious diseases caused by rickettsial species. This disease result in acute febrile illness and is transmitted by arthropod vectors like lice, mites and fleas.
Epidemic and murine typhus disease have common clinical manifestations. History of the patient may show many indicative features like occupational exposure, visit to endemic areas, overcrowding, or poor hygiene. War or civil unrest are found to be common risk factors in the development of rickettsiae infection. In epidemic typhus, the symptoms may be present in different systems. Fever and headache are the initial symptoms. In epidemic typhus a petechial rash may develop in the axilla 4-5 days after infection. The rashes may gradually spread to the trunk.
In scrub typhus disease, a small and painless papule develop at the site of mite bite. This may undergo necrosis and result in the formation of an eschar. Eschar is a confirmatory symptom in the case of scrub typhus. Eschar formation may be absent in around 40% of the patients and this makes diagnosis hard. Many other symptoms of this disease are non-specific. Localized lymphadenopathy is noted at the site of bite and this may develop into generalized lymphadenopathy. Pulmonary involvement is often noted in scrub typhus and hence patients may present with tachypnea and cough. Conjunctival suffusion also may be noted in some of them.
When left untreated, fever may be persistent and can be associated with relative bradycardia. Fever may persist for 2-3 days even after the start of antibiotic treatment. Maculopapular rashes spread from the axilla to the trunk and then to different parts of the body, except face, sole, and palms.
History of the patient with characteristic symptoms of the disease are very important in the diagnosis of typhus disease. Laboratory studies are more helpful in assessing the severity of the condition rather than confirmatory diagnosis of typhus disease. It also helps in differential diagnosis. Laboratory studies are useful in assessing the vasculitic changes caused by the infection. Some of the common abnormalities noted include proteinuria, leukopenia, thrombocytopenia, higher levels of transaminase, and hypoalbuminemia.
Acute primary disease is diagnosed using immunofluorescence assay (IFA) or enzyme immunoassay which may show an increase in IgM titer. Brill-Zinsser disease is confirmed with a history of primary epidemic typhus disease with an increase in antibody titer and also recurrent symptoms of typhus. The increase in the levels of IgM indicates secondary response. Biopsy and PCR helps in confirmatory diagnosis of the disease . Complement fixation test is useful in identifying the causative species of rickiettsiae. Chest radiography is used to assess the course of scrub typhus and is usually done one week after the onset of symptoms .
Antibiotics are the standard of care in the treatment of the disorder . Doxycycline and chloramphenicol are used as antirickettsial agents.
Prognosis of the disease often depends on the severity of the disease and also the health of the patient at the time of infection. More severe form of clinical features are seen with epidemic typhus. Patients with severe form of epidemic typhus may develop gangrene that leads to loss of limb or other appendages. Vasculitis may also result in neurological symptoms, multiorgan failure, and even death. Early diagnosis and treatment are good prognostic factors for any type of typhus disease. Starting antibiotic therapy as early as possible helps to improve the symptoms and to reduce mortality.
Typhus is caused by pleomorphic bacteria belonging to the group of rickettsiae. These are obligate intracellular parasites and may be cocci or bacilli in form. Epidemic typhus is caused by Rickettsia prowazekii . Body louse is the vector for this form of typhus fever, commonly Pediculus corporis, P capitis, and Phthirus pubis. Occasionally, flying squirrels are also found to harbor these bacteria . Bacteria gains access into a louse when the louse feeds on the blood of an infected person. The louse often dies of rickettsiae infection caused by obstruction of alimentary canal.
Brill-Zinsser disease is a recrudescent form of epidemic typhus. If the patient gets lice infestation at the same time, the louse may become infested by feeding and may result in an outbreak of the disease .
Murine typhus is transmitted by cat or rat flea and is caused by R typhi. Fleas Xenopsylla cheopis (rat flea), and Ctenocephalides felis (cat flea), well known to act as vectors for R typhi. Usual hosts for the bacteria are mice and cat. These fleas are not usually affected by the infection, unlike lice in epidemic typhus. Aerosol contaminated with fecal matter of fleas is a possible route of infection.
Scrub typhus is caused by the species Orientia tsutsugamushi spread through mites. The common vectors of these bacteria are Leptotrombidium akamushi and Leptotrombidium delicense. Mites are not affected by the presence of bacteria . Mammals like rats and mice are the usual hosts of the bacteria. Human beings are accidental hosts. The intracellular parasites are transmitted to the hosts during feeding. Many behavioral factors were found to be associated with increased risk of developing scrub typhus . Some of them include taking rest near scrubs, working with bare hands, wearing short-sleeved dresses, and squatting.
Epidemic typhus is more prevalent in Central and South America, Africa, the northern parts of China, and the central regions of Himalayas. About 15% of the people who have a history of typhus may develop Brill-Zinsser disease at a later stage. It may occur up to 40 years after the initial typhus infections. When conditions for transmission and propagation of the vector are conducive, epidemic typhus outbreaks occur. It is often associated with wars and other conditions that lead to poor hygiene that favor infestation of lice. This disease is often found in cold regions, poverty, and during civil unrest. Men and women are equally affected by this disease . Incomplete and inappropriate treatment of infection may increase the risk of recurrence, mostly in the form of Brill-Zinsser disease.
Murine typhus is more common in the coastal areas of subtropical and temperate countries. It is endemic in many areas and is mostly sporadic in nature. In temperate climates the population of fleas increase during summer months, thus increasing the incidence of the disease. Homeless people are at an increased risk of developing this form of typhus .
Northern Australia, Indian subcontinent and Pacific regions are more susceptible to scrub typhus. Many endemic areas of this disease lack appropriate diagnostic facilities, a condition which results in a serious underestimation of the incidence. In Malaysia, the incidence of scrub typhus was about 3% in a month. Multiple infections were found in the same individual indicating absence of cross immunity .
In general, typhus infections occur equally among males and females. Furthermore, there is no age predilection for the occurrence of this disease, even though in United States murine and epidemic typhus are found to be more common among adults .
Louse bite causes a pruritic reaction on the skin. Scratching of the site crushes the lice, and fecal matter containing the bacteria enters the wound. Rickettsia then moves to the blood stream where it parasitizes the endothelial cells of blood vessels. Incubation period for the pathogen is about 12 days. These bacteria then proliferate in the cells resulting in cell enlargement and multiorgan vasculitis. Deposition of leukocytes, macrophages and platelets occurs in the affected area resulting in small nodules. Proliferation of the bacteria may also result in thrombosis leading to gangrene in the extremities. Vasculitis is the reason for intravascular colloid loss, hypovolemia and reduced tissue perfusion. It may also lead to organ failure.
Some of the people who have suffered from a Rickettsia infection may develop recrudescent typhus, the Brill-Zinsser disease. Even after successful treatment of the infection, the bacteria may remain in the tissues. After several months, or even years, this bacteria may become active resulting in recurrence of typhus. The method by which the pathogen remains inactive and silent is not clearly known. The manifestations of Brill-Zinsser disease are less severe than the actual infection. Pathophysiology of murine and scrub typhus disease are similar to that of epidemic typhus.
Louse-borne infections can be prevented by de-lousing clothes and maintaining good personal hygiene. Avoiding contact with ticks and mites help in preventing diseases caused by them. Control of vectors and animal reservoirs are also helpful. Arthropod vectors can be controlled by the use of insecticides. Reducing rodent population, wearing protective clothing and avoiding overcrowding help in preventing the spread of the disease. Try to avoid exposure to areas endemic to the particular type of typhus disease.
Typhus is a group of infectious diseases caused by rickettsial species. This disease result in acute febrile illness and is transmitted by arthropod vectors like lice, mites and fleas. The most common among them are :
Epidemic typhus is a major threat to public health, particularly during war or a civil unrest. Brill-Zinsser disease is a mild form of recurrent epidemic typhus and is more prevalent among elderly people. Murine typhus is rat flea-borne and is more common in Southern United States, particularly in summer and fall. Clinical manifestations of murine typhus are similar to that of epidemic typhus, but are less severe. Both epidemic and murine typhus infections render the patient immune to subsequent infections. Scrub typhus is mite-borne and is more commonly found in Asia-Pacific region.
Typhus is a group of infectious diseases caused by by Rickettsia bacteria. This disease result in acute febrile illness and is transmitted by vectors like lice, mites and fleas. The most common among them are :
The signs and symptoms depend on the form of the disease. Antibiotics are the standard of care in the treatment of typhus.