Since there is evidence of a concerning upward trend in scrub typhus cases in Nepal, there is a need for enhanced surveillance, early diagnosis, effective treatment and preventive strategies to control the disease
Acute encephalitis syndrome (AES) is considered as a constellation of symptoms consisting of a sudden onset of fever, with change in the mental status (including confusion, disorientation, coma or inability to talk) and/or new onset of seizures in a person of any age. These features are used by clinicians to identify patients with suspected encephalitis. Although viruses are the most important cause, bacterial or parasitic infections orimmune-mediated processes of the brain can also cause encephalitis. One important yet largely ignored cause in Nepal is scrub typhus, which often causes outbreaks annually. Encephalitis occurs in approximately10 per cent of those infected.
Humans accidentally become hosts for scrub typhus when they pick up an infected larval mite while walking, sitting or lying on infested ground. It is a zoonotic disease, meaning it spreads from animals to humans and not person to person. It is caused by the bacterium Orientia tsutsugamushi, which is transmitted by mites of the Trombiculidae family, particularly Leptotrombidium deliense and Leptotrombidium akamushi.
The disease is mainly found in the 'tsutsugamushi triangle', an area covering parts of Japan, the Philippines, Australia, India, Pakistan, Afghanistan and southern Russia. Around one billion people are at risk, and there are an estimated one million cases every year. The risk of death can be up-to 50 per cent.
The bacterium is spread by larval mites, also called 'chiggers', which feed on the body fluids of infected rodents. These mites carry the bacteria and pass the infection to humans through their bite. The mites stay infected throughout their life, passing the bacteria to their offspring. Mite larvae feed by inserting their mouthparts into the host's hair follicles, injecting bacteria when they feed. The mites live in the soil, and the infection is maintained in nature through rodents and mites acting as reservoirs.
The bacterium enters the brain by disrupting the blood-brain barrier, which normally protects the brain from blood-borne infections. Thereafter it infects and damages the brain cells and alters the immune response, leading to symptoms of encephalitis. The symptoms generally appear 10-12 days after the bite, including fever, severe headache, vomiting, drowsiness, congested eyes, cough, muscle pain, shin pain, deafness and enlargement of the liver and spleen. The characteristic sign, called eschar, is a blackish ulcer found at the feeding site of the mite, mainly in the groin, armpits, genitalia and neck.
Recent times have seen a sudden resurgence of scrub typhus in different parts of Nepal. This could be because of climate change and altered environmental and geographical settings following the earthquake of 2015, which compelled people to live in temporary shelters in open areas exposing themselves to rodents and mites.
There has since been an ever increasing number of cases. In 2015, 101 cases were reported from 16 out of 77 districts with eight deaths. Subsequently in 2016, a total of 831 cases were reported from 66 districts with 14 deaths.Majority of the cases are found in low lying southern tarai region. The peak period wasthe months of August and September. Two types of rats, namely, Rattus and Rattus aquaticus are reported to be reservoirs of scrub typhus in Nepal. Based on collected samples from humans, rodents and chiggers, there is clear evidence of high transmission of Orientia tsutsugamushi, with the potential of an outbreak magnitude in Nepal.
Since Nepal also lies within the 'tsutsugamushi triangle', it is obvious to suspect endemicity of the disease.In 2023 alone, over 2,200 cases of scrub typhus were reported. Recently, people with scrub typhus encephalitis have also presented to the hospitals with other serious features, such as profuse bleeding and liver and kidney dysfunctions.
Diagnosis of scrub typhus encephalitis is made by brain scan (MRI/ CT scan) and lumbar puncture. Lumbar puncture is conducted by inserting a needle in between the vertebrae and withdrawing cerebrospinal fluid which circulates around the brain and spinal cord. Evidence of bleeding, raised inflammatory cells, elevated antibodies against Orientia tsutsugamushi and polymerase chain reaction for detection of Orientia tsutsugamushi in this fluid confirms the diagnosis.
It can be treated by administering an easily available antibiotic called Doxycycline. Severely ill people require hospitalisation, intensive care, anti-seizure medications for control of seizures and administration of intravenous fluids. They need to be closely monitored for complications such as seizures, brain swelling, electrolyte imbalance, breathing difficulty and choking.
The World Health Organisation cautions that the disease is re-emerging as a public health problem in rural Southeast Asia such as Myanmar, Indonesia, Thailand, India, Pakistan, Maldives, Sri Lanka and Nepal. New settlements after clearing forests, riverbanks and grassy areas have been observed to provide suitable setting for infected mites to cause intense disease transmission. Since there is evidence of a concerning upward trend in scrub typhus cases in Nepal, there is a need for enhanced surveillance, early diagnosis, effective treatment and preventive strategies to control the disease. Hence, all AES cases should also be screened for evidence of scrub typhus encephalitis in Nepal.
Dr Amod is with Nepal Medical College, Jorpati while Dr Ajit is a Professor of Pediatrics, National Academy of Medical Science, Kanti Children's Hospital