Parasites found on tiger’s body could reduce its fitness

Four types of parasite infections have spread in the tigers living in the Sundarbans while the animals preyed upon by the tigers, such as deer, wild boars, and monkeys, have also been found to be infected by parasites.

There is concern that this infection could weaken the tigers and reduce their hunting ability, according to a recent study.

The research on parasitic infections in tigers of the Sundarbans, other infectious diseases, related pathogens, and the spread of these infections, has shown that four types of parasitic infections are occurring in the bodies of Sundarban tigers.

These are roundworms, tapeworms, flukes, and protozoa. Among them, tapeworm infections are the most prevalent, found at 68. 5 per cent prevalence. This is followed by roundworm infections, at 53 per cent.

The study was jointly conducted by five researchers from Bangladesh Agricultural University, Sylhet Agricultural University, Khulna Agricultural University, Gazipur Agricultural University, and the International Centre for Diarrhoeal Disease Research, Bangladesh (icddr, b). Among them, some are parasitologists, some microbiologists, and some epidemiologists.

Samples from various wildlife, including tigers, were collected from the Sundarbans at different times from March 2024 to January 2025 for the study.

The primary aim of the research is to contribute to increasing the tiger population.

Researchers say that the natural agility and speed of tigers determine how smoothly they can hunt. The survival of tigers in the Sundarbans depends on their hunting ability. This ability could be reduced by parasitic infections.

The study was led by Professor Sultan Ahmed of the Microbiology and Immunology Department at Sylhet Agricultural University.

"These parasites that infect the tigers are known as ''silent killers". They do not cause death but increase the risk of it. If the amount of parasites in the body increases, the tigers will become weak. If they become weak, their hunting ability will decrease, and nutritional issues will arise in their bodies," he told Prothom Alo.

Today, 29 July is World Tiger Day. The day is observed globally each year to create awareness about conserving tiger habitats and the protection of tigers. This year's theme in Bangladesh is "Let's be aware, let’s conserve tigers."

The research states that the parasites reside in the tiger’s digestive tract and absorb nutrients from food, causing the infected tiger to suffer from malnutrition, lose weight, and become physically weak.

Prolonged infection can decrease the immunity of the tiger, increasing the risk of other infectious diseases. It can also have a negative impact on reproductive capacity and the survival rate of cubs.

The number of tigers in the Sundarbans is already low and they are at risk. This infection could make conservation efforts even more challenging.

Professor Sultan Ahmed mentions, "In the droppings of tigers, we have found a deadly parasite from the nematode group known as Toxocara cati, which can cause death in tiger cubs due to their lower immune capability.

Additionally, we found the worm Ancylostoma ceylanicum, which, residing in the intestines, sucks blood and causes diarrhoea. There is also the trematode group parasite, the liver fluke, which can significantly damage a tiger’s liver."

Professor Sultan Ahmed provided examples of how parasitic infections occur in tigers. Liver fluke parasites reside in snails. When snails climb onto grass, they position the parasites there. When deer come to graze, the parasites enter their body through the grass. When a tiger preys on the deer, the parasite enters the tiger’s intestine. This way, the infection spreads in the tiger''s body.

He also mentioned that parasites can spread in the Sundarbans from human and livestock feces as well.

Researchers collected fecal samples from tigers from 65 locations across four ranges of the Sundarbans in two stages. These samples were then analysed in laboratories at Bangladesh Agricultural University and Sylhet Agricultural University to confirm the presence of parasites, bacteria, and viruses, and to determine the types of microorganisms. In these two laboratories, fecal samples from a total of 399 animals, including tigers and their prey, were tested.

The research found that it’s not just tigers; deer have a 43.4 per cent rate of roundworm infection, while monkeys have a 61.3 per cent infection rate with both roundworms and protozoa. Additionally, wild boars showed 38.1 per cent incidence of roundworm infections and 47.7 per cent incidence of protozoan infections.

Researchers have suggested that canine distemper virus infection could be the most fatal infection for tigers. Evidence of this virus was found in blood samples collected from dogs in areas adjacent to the Sundarbans.

Professor Sultan Ahmed said, "Canine distemper virus was found in blood samples of dogs from areas near the Sundarbans. However, geographically, the Sundarbans are protected in such a way that there is no chance of interaction between tigers and dogs. Still, as a precaution, we recommend removing dogs within a one-kilometer radius of the Sundarbans.

Citing an example, Professor Sultan Ahmed mentioned, "In 1994, a canine distemper parasite infection caused the death of several lions, cheetahs, and jaguars in the Serengeti region of Tanzania. A similar incident occurred at a safari park in Japan in March 2010. Therefore, taking risks is not advisable. In addition to that, it is essential to regularly administer deworming and vaccinations to all livestock within 10 square kilometers of the Sundarbans."

Professor MA Aziz, an expert on tigers from the Department of Zoology at Jahangirnagar University, told Prothom Alo, "This research will play an important role in tiger conservation and increasing their population. Now, strategies need to be developed on how to reduce the threats to tigers based on the data obtained from this research."