A few days ago, a 40-year-old male was admitted to Sukraraj Tropical and Infectious Disease Hospital (STIDH), with a five day history of fever, severe headache, joint pain, red eyes and nausea. Examination revealed a scab known as “eschar” on his right thigh. He also reported shortness of breath on exertion. Serological testing confirmed a diagnosis of scrub typhus. Similarly, a 30-year-old female was admitted to STIDH with a five day history of high-grade fever, headache and severe abdominal pain. She also reported experiencing noticeable shortness of breath. Another female patient was admitted to STIDH with a seven day history of fever, who had also developed shortness of breath prior to the onset of fever. All these patients were residents of Kathmandu.

In the past, the majority of scrub typhus cases in Nepal were reported from sub-urban or rural areas. Nevertheless, in recent weeks, the STIDH laboratory has detected dozens of scrub typhus-positive cases daily among febrile patients in Kathmandu, indicating a rare but rapidly emerging outbreak. In other words, Kathmandu is currently facing one of its largest scrub typhus outbreaks.

Scrub typhus, caused by the bacterium Orientia tsutsutgamushi, is transmitted to humans through the bite of infected larval mites, commonly known as chiggers, with rodents as key hosts. Evidence from the study conducted by Nepal Health Research Council (NHRC) found chiggers in 25 percent of sampled rodents, highlighting significant outbreak potential. As rodents are common in Kathmandu households, future outbreaks are a distinct possibility.

Symptoms of scrub typhus typically appear five to 20 days after exposure to an infected chigger mite, with an average incubation period of 10-12 days. Fever with high-grade fever, rash, severe headache, red eyes, swollen lymph nodes, nausea/vomiting, profuse sweating are primary signs and symptoms of scrub typhus. Interestingly, I observed shortness of breath in almost all patients, a symptom often overlooked by healthcare providers. Perhaps, it typically presents in a mild form and is not included in the standard medical text books. However, during the 2025 Kathmandu outbreak, patients reported experiencing shortness of breath. Another prominent sign is the presence of a black scab, also known as “eschar” in the body, which develops at the site of a chigger mite bite.

Previously, I observed “eschar” marks on the chest, buttocks, groin, thighs and axillae area. In the current outbreak, eschars were present in one out of three patients (approximately 33 percent). In fact, many patients do not notice eschars. It is likely because they occur in less visible or unusual locations on the body.

Scrub typhus typically peaks during the monsoon season, coinciding with the circulation of other infectious diseases such as dengue, leptospirosis, typhoid fever, malaria etc. Consequently, primary symptoms often overlap, making clinical distinction based on symptoms alone challenging. However, the presence of high-grade fever, shortness of breath and an eschar strongly suggests scrub typhus infection, although serological testing remains essential to confirm the diagnosis. At present, no vaccine is available for scrub typhus; however, the disease can be effectively treated with antibiotics, which are readily accessible in Nepal.

Another concerning issue is the increasing trend of co-infection with dengue virus. At the moment, dengue virus is circulating alongside scrub typhus in Kathmandu. As a result, many patients with fever are being diagnosed with dual infections. Recently, two febrile patients from the same family tested positive for both scrub typhus and dengue, indicating dual infection. Their clinical symptoms resembled scrub typhus, whereas laboratory findings, including leukopenia, increased liver enzymes, and thrombocytopenia (low platelet count), were consistent with dengue. Both patients recovered uneventfully without hospitalisation.

Some studies have shown that co-infection with scrub typhus and dengue can lead to more severe illness, including pneumonia, meningoencephalitis and multiple organ dysfunction syndrome. Although co-infections are increasingly observed in Kathmandu, there has not yet been a significant rise in severe cases. However, the possibility of severe illness from such co-infections in the coming year cannot be ruled out.

The reasons for the increasing trend of scrub typhus in urban areas such as Kathmandu are not fully understood, though several factors are believed to contribute. Rapid urbanisation, climate change and increased rodent-human contact are likely to be the carriers of this disease. Human behaviors, such as visiting parks, gardening or hiking in nearby hilly areas, also increase the risk of exposure to chigger mites, which inhabit bushes and grassy ground. Conversely, indoor activities can also lead to scrub typhus, as rodents are common in Kathmandu households. Dozens of individuals presenting to STIDH with rodent bites highlight the prevalence of rodents in the city. Notably, most patients do not report engaging in outdoor activities, suggesting that transmission may occur indoors rather than being limited to outdoor exposure, as previously assumed.

On the whole, Kathmandu is currently experiencing an ongoing outbreak of scrub typhus after a long interval. There is also an increasing trend of co-infection, as dengue is circulating alongside scrub typhus. Although, severe illness from co-infection has not yet been observed, the possibility cannot be ruled out in the coming days. In Kathmandu, transmission of scrub typhus may predominantly occur indoors rather than through outdoor activities, as reported by the majority of patients. However, further studies are needed to confirm or refute this observation.