Lower species richness in deforested landscapes tied to high Kyasanur forest disease risk: study

High mammal species richness in the Western Ghats was associated with increased Kyasanur forest disease (KFD) virus risk but only in areas of low forest loss. In deforested landscapes, disease risk is tied to low numbers of species in a specific geographic area, says a new study.
There is good potential for cooperation between animal and human health infrastructure at the municipal level that could underpin a novel ‘One Health surveillance’ architecture and service delivery, according to the researchers.
There are challenges to implementing One Health on the ground; working models of One Health are needed to put the intersectoral approach into practice.

As outbreaks of Kyasanur Forest Disease (KFD) or ‘monkey fever’ rapidly expand across the Western Ghats, a study finds that in landscapes undergoing forest loss, a lower number of mammalian species is tied to high disease risk.

High mammal species richness in the Western Ghats was associated with increased KFD virus risk but only in areas of low forest loss which points to the role of forest loss in substantially tweaking the association between species richness and outbreaks. Landscapes of highest risk are those that have been subjected to diminished biodiversity following habitat fragmentation (i.e. forest loss).

“These landscapes tend to be dominated by species that are resilient to human pressure, as those that are less resilient and which can be found in areas of greater biodiversity tend to disappear as habitat is lost. These species that are more resilient to human pressure also tend to be species that are more efficient viral hosts because those aspects of their biology that make them resilient also make them more efficient hosts,” study’s corresponding author Michael Walsh, a landscape epidemiologist with the Sydney Institute for Infectious Diseases and the Sydney School of Public Health, told Mongabay-India.

The findings of the modeling study that estimates local mammalian species richness across the Western Ghats suggest narrowing down monitoring of wildlife to areas of marked habitat fragmentation across the Western Ghats states to develop wildlife surveillance infrastructure under the ‘One Health’ approach at the taluk (sub-district) level across the states.

Spread by infected ticks, the KFD affects people typically living and working in the Western Ghats, presumably due to greater human exposure to infected animals and ticks during January to June, before the onset of the monsoon. Haemaphysalis spinigera ticks are identified as the main vector. A wide range of small rodents, monkeys and birds are thought to play a role in Kyasanur Forest Disease Virus (KFDV) transmission. The disease first emerged in Kyasanur in Karnataka’s Shimoga/Shivamogga district in 1957 after the forest ecosystem was increasingly degraded by human activities.

Since 2012 the disease has spread to new districts in Karnataka and neighbouring states of Tamil Nadu, Goa, Maharashtra, and Kerala in the Western Ghats. Researchers at ICMR-National Institute of Virology (ICMR-NIV) chalk up the KFDV spread between states to movements of tick-infested monkeys in these forests along with changes in agricultural and occupational practices that encourage the proximity to humans and/or their dwellings.

Taluks identified as priority targets (red) for implementing animal-human surveillance in Karnataka state. Once the taluks are selected, One Health surveillance infrastructure can be developed by working in concert with the forest department, animal husbandry and veterinary services and with primary healthcare centres. Map by Walsh et. al.

Prashanth N. Srinivas at the Institute of Public Health, Bengaluru, who was not associated with the study adds that the results are not surprising but they are important. The findings are also broadly in line with a paper co-authored by Srinivas on predicting disease risk areas in Shivamogga district in Karnataka. It echoes that creation of habitat mosaics, when the forest is removed for paddy cultivation and plantations, precipitates the emergence of the KFD in humans.

“One of the primary factors that valuable for prediction is the change in purpose for which the land is used which typically happens for mega projects such as road construction or felling forest for rubber plantations versus small scale impacts that traditional forest dwellers have on the forest because they have a more organic relationship with the forest built on longterm association with the area,” Srinivas told Mongabay-India.

Template for ‘One Health’

The Western Ghats has lost evergreen forest cover from 16 to 11 percent from 1985–2018 due to human-caused actions. A simulation published in 2019 predicts the region will have merely 10 percent evergreen cover (in protected areas) in 10 years with agriculture (17 percent), plantations (40 percent) and built-up area (five percent) shaping the landscape in the future. In a recent publication, more than 200 medical journals warned that health is already being harmed by global temperature increases and the destruction of the natural world, a state of affairs health professionals have been bringing attention to for decades.

In 2019, India launched its One Health initiative, an intersectoral approach to tackling the most urgent health threats in the region, with a focus on low and middle-income countries across the south and southeast Asia and sub-Saharan Africa, based on WHO’s framework on the approach.

For the One Health approach to work on the ground, Srinivas argues for a working model. “We have been struggling with One Health on the ground while it is widely used in global literature. The human health department has not sufficiently engaged with the One Health approach; we have to convey what it is in a more meaningful way to make it practical for people on the ground.”

“We need working models of this surveillance within the rural districts where One Health is put into practice. It needs a template. For example, it could involve setting up a secretary-level committee for each state which meets every year to review a priority list of diseases for that state,” adds Srinivas.

He also emphasised an ecological approach to One Health, for example, a One Health committee for the Western Ghats, Trans-Himalayas and other landscapes could be set up to drum up necessary attention.

Kiran S.K., deputy director (KFD Nodal officer) of Virus Diagnostic Laboratory, Shivamogga, Karnataka explains that coordination with biodiversity boards at the village level is the way ahead in surveillance of wildlife and forest loss under the One Health approach. “For example, it can give us information if the numbers of animals that are hosts of the tick-borne virus are increasing or decreasing. It also gives the local communities a sense of responsibility and we can get good information from them because most of the affected villages are situated deep inside the forests,” Kiran said.

So far, the coordination is limited at the taluk and district levels. In 2018-2019, 445 human cases of the KFD were reported in Karnataka which dropped to 287 in 2019-2020; 2020-2021 was a “mild year” with 20 to 22 cases. Kiran says sensitisation drives and better surveillance at the village level were contributing factors to the decline of reported cases.

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Working with affected communities

“Earlier people used to notice the death of monkeys but not report. We started getting good information about monkey deaths and there was good vaccination coverage for the people in the last couple of years. Nature has also been kind to us. We had good rains and tick density seems to have come down in the last few years,” said Kiran.

Mujeeb Rahman, a social scientist who works with the KFD-affected communities in Karnataka and Kerala as part of the India-UK MonkeyFeverRisk project says earlier, monkey carcasses would be burned or buried by the farmers. “This put them at greater risk of contracting the KFD as monkeys are hosts for the KFD, and their carcasses and immediate vicinity would have an abundance of infected ticks. However, communities that are aware of these aspects, inform both the forest and health department and also take precautions,” said Rahman.

“Although forest use and forest-related occupations are correlated with the KFD, it has to be kept in mind that the local communities in these areas who contract the KFD are often marginalised groups with few viable alternatives with respect to livelihoods,” Rahman, a research associate at the Ashoka Trust for Research in Ecology and the Environment (ATREE), Bengaluru, told Mongabay-India, adding that prohibitions such as blanket bans that undercut access to forests are likely to be harmful to these communities.

In Kerala, for example, the Cholanaikka tribe, with which Rahman works, live very close to the evergreen climax forest (between teak plantations and the forest). Their earning comes from forest products like honey harvest, medicinal plants, teak flowers, lichens, fishing, and amla or Indian gooseberry. In Karnataka, the smallholder families who reside in the forest periphery are vulnerable to the KFD. They are not heavily dependent on the forest itself for their livelihoods but are closely linked with the forest for other purposes including grazing livestock. “Livestock is allowed to graze in the forest and they return on their own in the evening likely carrying more hard ticks into living spaces and properties,” points out Rahman.

Members of a tribal community in the Western Ghats which lives along forest margins. Photo by Mujeeb Rahman. — Members of a tribal community in the Western Ghats that lives along forest margins. Photo by Mujeeb Rahman.

Rahman notes that as primary stakeholders, communities and their representatives should be allowed to play an inclusive role in decision-making concerning the KFD. They also have the potential to play a very significant role in various aspects of the KFD surveillance as well as mitigation.

“In Karnataka, for example, in places such as Sagar, Shivamogga, the hamlets are widely spread across remote areas and some are also located at the periphery of the forest. Due to their remoteness, these hamlets may not be in a position to receive information provided by ASHA workers/ or primary healthcare centres about monkey deaths or to report the occurrence of monkey deaths to the authorities,” he said.

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Looking beyond monkeys for surveillance

While large monkey die-offs (Macaca radiata, Semnopithecus hypoleucus, and Semnopithecus priam species) are powerful indicators that KFDV is circulating in the landscape, Kiran, the KFD Nodal Officer in Karnataka, says that enhanced surveillance would need to go beyond monkeys.

“Monkeys die within 10 to 15 days of the infection and the distance covered by the monkeys is very short (five to 10 kilometres). So we need to consider other potential species that may carry the ticks, including leopards and chital as the study (by Walsh et. al) indicates.”

Leopard (P. pardus) abundance and relative abundance and chital (A. axis) abundance were also associated with outbreak risk. While neither of these species has been shown to be susceptible to the KFDV, both are known to host the KFDV-relevant ticks and distribute these vectors in the landscape, the paper said.

Kiran’s point also has context in terms of the affected communities’ close association with the forests and exposure to virus-carrying ticks circulating in wildlife.

For instance, wild animals like spotted deer, primates, Indian giant squirrel or Malabar giant squirrel, shrews, rodents and peacocks which carry the same ticks are common visitors to properties in forest fringe areas in Kerala where the Cholanaikka tribe lives. ”And some of the families live inside the forest and all their livelihood activities result in exposure to infected hard ticks that are reservoirs of KFDV,” Mujeeb Rahman of ATREE observed.

In Karnataka, smallholder families also collect dry leaves from the semi-deciduous forest to line the floor of their cowsheds and to get more quantity of cow dung manure through mulching. “Women also visit the forest for collecting firewood. This is also an activity that increases their exposure to ticks which usually live under the dry leaves. The mixed cropping pattern of the smallholders (e.g. banana and areca nut cultivation) also attracts primates. The paddy harvest season that also coincides with the increased presence of rodents matches with the KFD outbreak season,” shared Rahman.

Michael Walsh echoes Kiran and others in saying that the understanding of the KFD is stunted because little is known about which species comprise its wildlife reservoirs and how the virus circulates in nature. “We need to increase this knowledge base (and quickly) because the KFD outbreaks are rapidly expanding across the region and the infection ecology and effective epidemiological interventions are currently both insufficient to stem this growing problem,” he said.

“Moreover, the KFD is just a model example of a much larger problem globally, which is that we know very little about the infection ecology of many (probably most) zoonotic pathogens and therefore we cannot craft optimal epidemiological interventions. Developing surveillance within a One Health framework offers a tenable solution for the KFD, and other zoonotic pathogens, because it simultaneously recognises the connections between humans, animals, and the broader ecosystems in which they live so that both the pathways to better understanding and the solutions for control and prevention that are based on that improved understanding are fundamentally grounded in all three.”