Parasites Pose Silent Threat to Endangered Bengal Tigers

Parasitic infections are acting as silent killers for endangered Bengal tigers, particularly when the animals are weakened. Research from South Asia links the threat to human settlements encroaching on tiger habitat, which help disease transmission from domestic animals.

Researchers analyzing fecal samples from wildlife in Bangladesh's Sundarbans mangrove forest detected an 85.3% parasite infection rate in Bengal tigers. The study, published by the Bangladesh Forest Department in July, was conducted in two phases in 2024 and 2025. It found the following infection rates across species:

Molecular analysis identified roundworms, hydatid worms, liver flukes, and parasitic tapeworms as the predominant species infecting the wild animals. Sultan Ahmed, a professor at Sylhet Agricultural University and study author, told Mongabay the key recommendation is "to keep the mangrove forest away from human interference."

Human Proximity Fuels Transmission

The study found households near the Sundarbans were, on average, about 450.7 meters from the forest, with a median distance of just 100 meters. This proximity and shared environments between domestic and wild animals help pathogen transmission across species.

Parag Nigam, Head of the Department of Wildlife Health Management at the Wildlife Institute of India, observes that domestic cattle, buffalo, and free-roaming dogs serve as primary reservoirs for parasites. These spill over into shared pastures and water sources. "The most effective baseline measure is managing the livestock buffer surrounding tiger reserves," he told Mongabay. A separate 2025 study on tigers in Maharashtra, India, warned such infections can cause chronic malnutrition, affect fitness and reproductive success, and in severe cases lead to death.

Research extends beyond India and Bangladesh. A 2025 study in Nepal's Chitwan National Park found proximity to human settlements intensifies zoonotic transmission risks. Babita Maharjan, an assistant professor at Tribhuvan University and study author, explained that wildlife-livestock interaction may increase infection risk for tigers directly through consumption of infected livestock and indirectly through shared habitats.

An unusual case from 2018 involved a Bengal tiger in Bhutan dying from neurocysticercosis, caused by a human pork tapeworm. A 2021 analysis said the mechanism was unknown but suggested the tiger may have ingested infective eggs through contaminated water or food. Camera-trap records showed the tiger's range extended to the outskirts of populated Thimphu.

A Drain on Tiger Health

Wildlife health expert Parag Nigam said parasites are a real issue, though poaching and habitat loss remain bigger threats. "That said, you can't just ignore these parasites either," he said. "They act like a slow, quiet drain on a tiger's health."

A strong, adult tiger can usually handle a basic parasite load. Problems arise when the animal is old, injured, or undernourished. Parasites then weaken it further, causing severe anemia and ruining hunting ability. A weak tiger may turn to village cattle, triggering human-tiger conflict. Parag explained the bigger worry is for cubs and isolated reserves. "Roundworms and flukes can easily kill young cubs before their immune systems even build up, which hits the local tiger population growth hard," he said.

Zoologist Babita Maharjan warned parasitic infections are a serious conservation concern, particularly for immunocompromised, injured, or nutritionally stressed tigers. "Multiple infections are often more damaging than single infections, can weaken the immune system, and make an animal more susceptible to additional diseases," she said.

Recommended Prevention Strategies

Study author Sultan Ahmed suggested an integrated, long-term wildlife disease surveillance program for the Sundarbans to monitor tigers and their prey. He advised parasite control in livestock and domestic animals around the forests, periodic de-worming of forest staff, and establishing a Central Wildlife Disease Diagnostic Laboratory.

Parag Nigam emphasized landscape-level strategies over direct veterinary care. He recommended routine, non-invasive monitoring via fecal samples collected during annual surveys. Prey population management also plays a vital indirect role. "When wild prey is abundant and easy to hunt, tigers remain in peak physical condition, allowing their immune systems to naturally suppress and tolerate endemic parasite loads," he said.

To support prey management, he suggested active grassland and water-body maintenance to sustain wild ungulate densities, rigorous disease surveillance in prey, and maintaining clean water flows to limit vectors. Educating forest communities about proper grazing, hygiene, and livestock de-worming can further reduce risks at the human-wildlife boundary.