Profile: Mark Nelder

Research in Action

14 June 2017

Insects often make people squeamish, but not entomologist Dr. Mark Nelder, a senior program specialist at PHO. He has been fascinated with insects throughout his academic life, and has devoted his study to their role as carriers of human and animal disease.

Nelder, and PHO colleagues Hetal Patel and Dr. Beate Sander, recently published a study in Lancet Infectious Diseases, which, for the first time, looked at the long-term lasting effects of West Nile virus (WNV). According to Nelder, “West Nile virus is a fairly new disease in North America. Most of the research up to now has been about the acute phase—what happens when people go immediately into the hospital. We wanted to know what happens when they go home.”

The study, Long-term Sequelae of West Nile Virus Illness: A Systematic Review, looked at the long-term physical, cognitive and functional outcomes of people infected with WNV, and in particular, the risk factors of people who ended up with poor outcomes. Outcomes included long-lasting muscle pain, muscle aches, loss of muscle strength, depression and forgetfulness. Major risk factors included being male, over 50 years of age, having longer hospital stays, heart disease and cancer.

Nelder hopes the study will help clinicians identify some of these risk factors and chronic conditions earlier so patients can be managed appropriately to increase their quality of life and functionality. He and his collaborators also identified a lack of good quantitative research on these long-term impacts, noting an opportunity for larger case-control studies to identify risk factors for West Nile infections.

Ontario is well-positioned to study insects given its substantial collection of data, says Nelder. “When I first came here, I was like a kid in a candy store. We have access to so much data. Ontario has been collecting mosquitoes for over 10 years now. We have millions of records of mosquitoes and we can relate that to disease incidence and risk. A lot of places just don’t have data on kinds of mosquitoes and changes in mosquito populations.”

Current research is focused on understanding which mosquitoes are transmitting diseases, and where and when people are at risk. “It’s the same with ticks; we are starting to better understand the distribution of ticks in Ontario, what pathogens they transmit and which ones pose risks to the public.” Nelder is currently investigating other pathogens associated with blacklegged ticks in North America; the spread of the Ochlerotatus japonicus, an invasive mosquito in Ontario; and evaluating the health and economic burden of West Nile virus illness in Ontario.

Ultimately, the study of all insects, known as vectors, is important to public health. “We have to continuously be on top of them,” cautions Nelder. “Before West Nile virus was discovered in Ontario, we had no major diseases from mosquitoes. We’ve stepped up our mosquito surveillance to respond to a public health threat. But there’s a lot more than West Nile that can be a threat to Ontarians. With rapidly changing climates we have to monitor other jurisdictions to see what insect threats might impact Ontarians.

“Some jurisdictions in North America dropped surveillance of vector-borne diseases, only to get large outbreaks years later. Surveillance programs are essential to understand trends and inform risk,” he says. “Thankfully, in Ontario we have a robust and growing program of surveillance. Reports like PHO’s Vector-Borne Disease 2014 Summary Report and WNV Weekly Surveillance Report, in addition to peer-reviewed research, enhance public health understanding of vector-borne diseases.”

PHO in Action: Mark Nelder

Dr. Mark Nelder discusses his work and how insects are carriers of human and animal disease.

Duration: 2 min

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Updated 14 June 2017