Scrub typhus: An emerging scourge

Scrub typhus is mainly treated by antibiotics which is the best way to prevent this disease because it slows down the multiplication of the organism and as a result the patients develop immune response

Scrub typhus, is an acute infection that is caused by Orientia tsutsugamushi(formerly known as Rickettsia), a gram negative proteobacterium.

It is also known as tsutsugamushi disease. “Tsutsuga” means small and dangerous, and “mushi” means insect or mite. The name scrub typhus was derived from the type of vegetation (terrain between woods and clearings) that harbors the vector.

Humans are accidental hosts of this zoonotic disease. This obligate, intracellular, gram-negative bacterium has a large number of serotypes.

This pathogen does not have a vacuolar membrane; thus, it grows freely in the cytoplasm of infected cells and can live only within the cells of other animals.

When larval stage mite (Leptotrombidium delicense) bites human, the bite of this mite leaves a characteristic black eschar (a dry, dark scab or falling away of dead skin) of about 5-20 mm in diameter. And this may be considered as an important clinical finding for the diagnosis of scrub typhus.

The site bitten by chiggers (i.e. tiny, 6-legged wingless larvae that mature to become a type of mite and are found in tall grass and weeds) is initially a papule followed by a blistered ulcer, and this is then covered with a black crust.

A million cases are reported and billions of people are at risk of this disease. Cases have been reported from different districts of Nepal at different times. According to Epidemiology and Disease Control Division (EDCD), six cases were reported as scrub typhus from eastern part of Nepal in September 2015.

This year more than 400 cases have been found and it has cost the lives of at least 13 people till date. Nepal is in the region of high risk for the spread of this disease. Being an agricultural country, many people come in contact with rodents, ticks and mites daily.

In the rainy season, bushy areas serve as a good habitat to those vectors.

The primary host for the transmission of this disease is Chigger mites. Once they are infected in nature by feeding on the body fluid of small mammals, including the rodents, they maintain the infection throughout their life stages and, as adults, pass the infection on to their eggs in a process called transovarial transmission.

Similarly, the infection passes from the egg to the larva or adult in a process called transstadial transmission. Chigger mite populations can autonomously maintain their infectivity over long periods of time.

Then the germs are transferred in human when they bite. The bite is usually painless.

There is no report of transmission of scrub typhus from human to human. The larval stage of mites serves as the medium to transfer the disease from human to other vertebrates.

The bite of these vectors like rodents, ticks, mites, louse, are mainly found in the neck, genitalia and groin region of humans.

A painless black eschar is usually seen in the regions of insect bite. Signs and symptoms of this disease includes maculopapular rash (a type of rash characterized by flat red area on the skin that is covered with small confluent bumps. A high grade fever (   >104F) is seen that persists up to 14 days of infection.

The illness begins with shaking chills, high fever, severe headache, profuse sweating, swelling of major lymph nodes (neck region and groin). The incubation period of scrub typhus is 10-12 days on an average.

The diagnosis of scrub typhus can be made by different serological tests.

For the rapid identification of the disease, diagnosis kits are available and are well accepted which can give results in an hour. The organism can be grown in tissue culture or mice from the blood of patients with scrub typhus but the results are not available on time to guide clinical management.

Scrub typhus is mainly treated by antibiotics which is the best way to prevent this disease because it slows down the multiplication of the organism and as a result the patients develop immune response.

The patients can be cured properly if they are diagnosed early and treated with antibiotics on a regular basis. Without early diagnosis and proper medication, the disease can be fatal. No effective vaccines are available for this disease till date.

Scrub typhus cases are more likely to occur in people living close to bushes and wood piles, farmers, rodent observers and those rearing domestic animals. So, as far as primordial prevention is concerned, the best measure would be to avoid going to such places like farms, areas abundant with bushes, rodents and domestic animals.

Public awareness is the main approach to control the spread of this disease.

First of all, the vegetation around houses should be cleared and spraying of insecticides should be done. Scrub typhus is easily curable and preventable if there is rapid identification by health-care workers, public education on case recognition and personal protection, rodent control and habitat modification.

Nepal Government should initiate the control strategies to control the spread of scrub typhus in coordination with other bodies and should provide the diagnostic kits to all susceptible areas as soon as possible to diagnose and prevent the further spreading of this disease.

Good personal hygiene and proper sanitation around the houses are the major ways for the prevention of all such types of diseases.

Lamsal is with Central Department of Biotechnology, Kirtipur