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Scrub typhus is an infection caused by Orientia tsutsugamushi, a bacteria transmitted by the bite of an infected chigger mite. Characterised by a variety of symptoms and a high mortality rate, scrub typhus is an underfunded, neglected tropical disease not even listed by the WHO. Better diagnostic tests and optimised treatments are being developed since no vaccine is currently available.

My name is Tri Wangrangsimakul, I am an infectious diseases and microbiology doctor, I am based in Chiang Rai in northern Thailand, the northern most Province in Chiang Rai and I mainly research a disease called scrub typhus.

Scrub typhus is an infectious disease caused by a bacteria called Orientia tsutsugamushi. Humans catch the disease through the bite of an infected chigger mite, a very tiny insect that you can barely see with the naked eye. Sometimes patients develop a skin lesion called an eschar, similar to a cigarette burn at the site of the bite. It usually occurs in rural areas and agricultural workers are the ones at most risk.

The disease is characterised by fever, patients can have an eschar or not, and patients also develop other non-specific symptoms such as a rash, cough, swollen glands and headache. The mortality of the disease ranges depending on where you are within the endemic area. In northern Thailand it can be as bad as 13%, which is quite high. The northern region accounts for 50-60% of these cases, despite only containing 20% of the population, so it is a major problem in northern Thailand. You don’t develop natural immunity to scrub typhus, which is long term, so if you live in the endemic area and you have ongoing transmission risk, such as an agricultural worker, you can catch the disease year after year after year.

We treat scrub typhus normally with specific antibiotics, the main one being called doxycycline which has been around for a few decades. The problem is, none of these antibiotics are first line antibiotics so if you or I develop a fever within the endemic area and go to hospital, we’re most likely to receive another class of antibiotics, similar to penicillin, and these antibiotics have no action against scrub typhus.

The most important lines of research in relation to scrub typhus are epidemiology and diagnostics. Diagnostics with scrub typhus is actually not that easy. The rapid tests available have a range of accuracy, and the current one we’re using is probably one of the better ones that we have but it’s just a screening test. To diagnose scrub typhus, we usually collect blood from the patients when they’re sick, followed by another blood sample maybe a couple of weeks down the line when they’re better, and assess for the antibody levels in response to scrub typhus infection. That remains the gold standard that has been in place for decades and we need to do better. One of the areas where we’re looking to improve is to provide a low cost, accurate test for clinicians to use at the place where it’s needed the most, i.e. in the district hospitals, in the clinics within this endemic area.

We talked about the ‘tsutsugamushi triangle’ and it was such a surprise to hear reports of scrub typhus being diagnosed firstly from the United Arab Emirates in the Middle East, and even more of a shock to hear that cases were being diagnosed in Chile in South America. There’s also been tentative cases diagnosed from Africa. This has really opened up the span of scrub typhus: it might be much more widespread than we originally thought.

Scrub typhus is a neglected tropical disease, so neglected in fact that the World Health Organisation does not have scrub typhus listed as one of the official neglected tropical diseases. As a disease that’s been under-researched and underfunded for decades, we are light years away from being in the position of other major diseases such as HIV, TB and malaria. The fact that drug resistance has been reported, and the fact that there are no effective vaccines currently available means that we need to progress with what we’re doing and accelerate the amount of research we are doing in scrub typhus.

We have come a long way in developing new tests for scrub typhus, particularly in the research setting where we need to be absolutely certain as much as possible that the patient has scrub typhus or not. Unfortunately a scrub typhus vaccine that is effective and ready to roll out is still many years away. In Chiang Rai the majority of our studies are clinically related studies, aimed at either answering clinically related questions and how we can improve the management of patients, or we’ll end up with improvements in diagnostics, in treatment. So we try to maximise the potential benefits in every study, and we realise that we need to collaborate more and more, especially in an area which is underfunded.

Tri Wangrangsimakul

Dr Tri Wangrangsimakul heads our satellite research unit in Chiangrai, Thailand, a region endemic for tropical rickettsioses such as scrub typhus. Although easily treatable with antibiotics, scrub typhus causes a significant health burden in the Asia-Pacific region where a billion people are estimated at risk. Research projects include the study of the immune response and the characterisation of drug resistant infections.

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