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Health agencies need to take into account disease evolution in warming environments as climate change could alter the development of vector-borne diseases, two studies have found.
The “vector” in a vector-borne disease refers to an infected human or animal that transmits pathogens or parasites and causes disease in human populations.
Climate change can impact “all relevant aspects” of vector-borne diseases, including the locations of host populations and the availability of vectors, says Nina Fefferman, a biologist and part of a team from Rutgers University in the United States behind one of the studies.
The research focused on Aedes japonicus japonicus, a species of disease-carrying mosquito native to Japan and Korea, whose range has expanded since the 1990s to parts of Europe and the Hawaiian archipelago. The study found that populations of the mosquito on the island of Hawaii and in the American state of Virginia were capable of “rapid evolutionary change” and adaptation to their new environment.
As a result, vector-borne disease could become a greater threat to human health as the global climate warms, the study found. Its authors say that climate change studies need to play a greater role in national and global efforts to eradicate these diseases.
“We have to understand the changes to each facet [of vector-borne disease] separately, and then how the different alterations interact with each other,” Fefferman tells SciDev.Net. “This is very complicated, but our current methods for vector-borne disease estimation don’t include many, if any, of these factors, even in isolation.”
Vector-borne diseases, which are typically found in the tropics and subtropics, account for 17 per cent of the world’s infectious disease burden, according to the WHO. The deadliest vector-borne disease is malaria, which killed an estimated 627,000 people in 2012, and the fastest growing is dengue fever.
The study, along with a second one focusing on how weather and climate variables are being included in the fight against vector-borne diseases, were published last week (16 February) in Philosophical Transactions B.
The second study calls for more applied research, rather than pure modelling, to assess the effectiveness of interventions and health-policy approaches to vector-borne diseases. It analysed work done under the WHO’s TDR (Special Programme for Research and Training in Tropical Diseases), which studies links between climate change and human vulnerability to diseases such as malaria, sleeping sickness and schistosomiasis (bilharzia).
The study found that the use of scenario-based modelling of disease outbreaks, based on past experiences, is of limited use for future decision-making, as there are too many uncertainties around disease behaviour in warming climates.
Madeleine Thomson, a researcher at Columbia University in the United States, says the WHO study makes a “compelling case” for how the health sector might respond to climate change. But shaping such a response requires high-quality and large-scale data sets, which are so far largely lacking, Thomson says.
She believes that, in malaria’s case, having such data sets would also help pay for disease control programmes, as they would enable these programmes to align better with national development agendas.
“Evidence of the return on investment is critical to obtaining funding and to do that one needs access to good surveillance data — something which is only just now beginning to be prioritised,” Thomson says.