Why A Western Ghats Initiative Could Have Lessons For Zoonotic Disease Control
Bengaluru: Kyasanur Forest Disease (KFD) is a tick-borne disease that occurs only in the Western Ghats, annually infecting about 500 people of whom 5% die. It is possible to predict the patterns of outbreak of KFD, a zoonotic disease like COVID-19, with a high degree of accuracy and control it by using an effectively targeted vaccination programme, new research has shown.
The risk maps developed by the team, consisting of multiple research organisations and governmental bodies, were successful at predicting KFD hotspots in two towns--Tirthahalli and Sagara--located in Shivamogga district in central Karnataka.
This is a pioneering effort at mainstreaming the advantages of cross-disciplinary initiatives to predict areas of high vulnerability, said Abi T Vanak, a senior fellow at the Ashoka Trust for Research in Ecology and the Environment and one of the authors of the paper.
KFD’s symptoms include a two-stage fever with the second stage leading to complications such as internal hemorrhaging. Sometimes, neurological symptoms also manifest. The outbreaks occur every year in the dry season from November until around May, according to the researchers.
The disease was first discovered in the late 1950s in the Shivamogga area and then it spread to neighbouring areas. “Earlier, the disease was found only around Shivamogga but over the past 10 years or so, KFD has been reported from parts of Western Ghats in other states like Kerala, Goa, Maharashtra,” Vanak said.
“KFD damages the health and livelihoods of the communities that live in and around the Western Ghats such as small-holder farmers, forest workers, migrant agricultural labourers and tribal groups that harvest non-timber forest products,” explained Bethan V Purse, lead author and ecologist at the Centre for Ecology And Hydrology, United Kingdom.
In the ongoing season, the team identified potential hotspots of transmission prior to actual outbreaks that allowed decision-makers across sectors such as public health, animal health and forestry to “view data on human cases, risk factors and predictions, tick and monkey surveillance, to inform their management”, said Purse.
“There is no antiviral for KFD but there is a vaccine,” said S.L. Hoti, a scientist with the Indian Council of Medical Research’s National Institute for Traditional Medicine (NITM), and one of the authors of the paper. “So, the best thing to do is vaccinate people before actual outbreaks. The tool we have developed takes into account environmental and social factors to predict cases so that public health officials can take preventive measures like vaccination.”
Earlier, vaccination and awareness programmes were conducted within a 5-km radius of actual human cases. This time, because of the risk maps developed by the team, vaccination programmes could be conducted before the outbreak season.
A call for proposals with similar models based on disease surveillance and identification of potential hotspots has been put out by the Department of Science and Technology for coronaviruses, Hoti said.
The risk maps that the team developed took into consideration historical patterns in KFD and other geographical risk factors such as types of forests and plantations, the altitude, the amount of forest loss and the densities of people and cattle. Public health factors such as proximity to health centres were also taken into account.
The dynamics of zoonotic diseases are changing in many inter-linked ways because of habitat encroachment, intensive agriculture, forest loss and degradation, global trade and climate change, said the researchers. And so, unpacking these “evolving burdens of zoonotic diseases and managing disease outbreaks requires a combination of many kinds of expertise and active exchange of knowledge and tools between researchers, practitioners, local communities and decision-makers”, said Purse.
Beyond maps and models
Workshops were conducted by the research team with stakeholders from health and forestry departments across states such as Karnataka, Maharashtra and Kerala where risk factors were identified and ranked.
Zoonotic diseases are “ecologically complex, dynamic systems, involving animals and sometimes arthropod vectors [species such as ticks and insects that transmit pathogens from infected animals to humans or other animals] in transmission, where each species involved may respond differently to habitats and ecosystems”, as per Purse. In the case of such disease research, “maps and models often remain in scientific literature and don’t inform policy”, she noted. “We have tried to avoid this by co-producing and iteratively validating our models with stakeholders and decision-makers.
In November 2018, the Indian government launched ‘One Health and Zoonoses’, its own interdisciplinary programme to study zoonotic diseases based on the World Health Organization’s (WHO) framework, IndiaSpend reported in March 2020. One Health initiatives that explore zoonoses from various angles, specifically including human and animal health, ecology and sociology, are the most effective and the most thorough means of tackling outbreaks such as KFD and COVID-19, according to experts.
The research work on KFD was conducted as part of Monkey Fever Risk project, an interdisciplinary One Health Indo-UK partnership between UK Centre for Ecology & Hydrology, the Karnataka Government's Department of Health and Family Welfare Services, NITM and National Institute of Epidemiology, the Indian Council for Agricultural Research’s National Institute of Veterinary Epidemiology and Disease Informatics and the Ashoka Trust for Research in Ecology and the Environment.
“This is a proper OneHealth partnership,” said Vanak, who is also leading India’s One Health and Zoonoses programme under the National Mission on Biodiversity and Human Well-being. The One Health framework was officially recommended as an approach to deal with zoonotic infectious diseases by the WHO in 2008 by bringing together experts working in human health, animal health, plant health and the environment. The core components of the framework are food safety, zoonoses and antibiotic resistance.
Links between deforestation and KFD
The impact of the disease, combined with the recent spread and evidence of widespread transmission, “make it urgent to understand the landscape conditions and social factors that precipitate disease in humans and to map out who is at risk and where”, said Purse.
In the study, the researchers focussed on deforested landscapes and areas that had large densities of grazing cattle in the district of Shivamogga. “We were particularly interested in the impacts of deforestation on KFD because initial emergence and large outbreaks in the last century followed forest clearance for roads, settlement, plantations and other types of cultivation,” Purse noted.
Landscapes that had the highest risk of human infection were forest mosaics with large amounts of moist evergreen forest and plantations, small amounts of dry deciduous forest and high densities of cattle, the researchers found.
“We sampled ticks from many areas to understand their abundance, risk of transmission, etc,” Vanak said. “We sampled rodents to understand tick-rodent association and we sampled livestock to see how many could act as hosts for ticks.”
A feature of KFD occurrences is that cases continue in one area spanning 20-30 sq. km. for a few years and then pop up in a new area and then the pattern is repeated. In this research, Tirthahalli was the original focus where cases have occurred from 2014 to date; Sagara, 50 km away was the location where cases popped up in 2019 and where they had not been recorded for 12 years.
“The model was trained on the Tirthahalli data but was able to predict the Sagara hotspot before it occurred,” Purse noted. The model also predicted new cases in Tirthahalli.
The need for interdisciplinary collaborations to tackle zoonoses
The virus that causes KFD is found in a large reservoir of hosts such as rodents and birds, and ticks act as intermediary hosts that transmit the virus to humans. Interactions with forested landscapes for food, fodder, fuelwood, etc. are the activities that expose communities to tick-carrying pathogens.
The disease is also called Monkey Fever because monkeys are a sentinel species for this virus. “Monkeys have the potential to become amplifying hosts,” Vanak pointed out. A reservoir host is one which carries the virus but does get sick because of it, Vanak explained. But when a monkey is bitten by an infected tick it can get sick and die, all the while carrying a high viral load. Then when ticks feed on a dead monkey, they get infected with the high viral load that they then transmit to humans.
“From day one, we partnered with the department of health and family welfare services and this is why the uptake of the research is high,” Vanak elaborated. “Local partners and those who are involved in implementation action are part of the project and therefore, action can be immediate.”
“We can assess the situation and suggest preventive measures to the public health department, state governments and local bodies,” said Hoti on the role public health experts can play in curbing outbreaks of diseases such as KFD. Public health experts can also engage in disease surveillance on a seasonal basis to forewarn local communities about possible outbreaks, he added.
This is an exemplar framework and we need to look at other zoonoses through similar, One Health approaches, Vanak said. “We aim to expand this work into other zoonoses like leptospirosis and scrub typhus in the next few months,” he added.
(Pardikar is a freelance journalist from Bengaluru.)
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