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The Dose Transcript for September 5, 2024

Host: Dr. Brian Goldman

BRIAN GOLDMAN: Hi, I'm Dr. Brian Goldman. Welcome to The Dose. For the most part, mosquitoes are annoying insects. Just thinking about mosquitoes makes me itch. But they also transmit West Nile virus and another virus called eastern equine encephalitis. Recently, a New Hampshire resident died from the virus, which is spreading across several New England states. So this week we're asking, why should I be concerned about mosquitoes? Hi, Sumon. Welcome back to The Dose.

DR. SUMON CHAKRABARTI: Thank you so much. It's great to be here.

BRIAN GOLDMAN: I don't know if I've ever asked you this question. Are you someone who regularly gets bitten by mosquitoes?

DR. SUMON CHAKRABARTI: Weirdly enough, no. And I know that especially more now, because my wife does get bitten a lot so I can see the contrast.

BRIAN GOLDMAN: You know, it's a weird thing. I don't know, is it pheromones? What is-- it's sweating? What is it that makes some people more susceptible to being bitten by mosquitoes than others?

DR. SUMON CHAKRABARTI: I think that you hit on it. It's multifactorial. I think that there's no definitive answer, but it's likely a combination of, for example, pheromones is part of it. The composition of the bacteria on your skin. Body heat. So, people who tend to be a bit bigger, they're putting out more CO2. That's another thought. These types of things can all attract mosquitoes. There's theories that, for example, if you're diabetic and your blood is a bit, quote unquote, "sweeter," all of these things have been brought up. I don't think there's a single explanation, but it's likely based on those factors.

BRIAN GOLDMAN: So I guess I'm kind of a ho-hum lunch when it comes to mosquitoes. They can take me or leave me, and I suppose I should be grateful for that. Onto more serious things. Before we begin our conversation, can you give us a Hi, my name is. Tell us what you do and where you do it.

DR. SUMON CHAKRABARTI: So I'm Sumon Chakrabarti. I'm an infectious diseases physician at Trillium Health Partners in Mississauga. I do infectious diseases, but I also have a special interest in tropical infections, which technically West Nile virus once was. And we'll talk about that later today.

BRIAN GOLDMAN: We'll get into that in just a moment. But what are the most common mosquito-borne diseases that are circulating in Canada? I suppose West Nile must be at the top of the list.

DR. SUMON CHAKRABARTI: Absolutely. So the thing to remember: in general, these are relatively rare infections, but we have four big medically important ones in Canada. So you have your West Nile virus. Also, eastern equine encephalitis virus. These are kind of the ones that you hear a lot. There are two other ones, and I've really only seen one of them to be honest, in my practice. They're called the California serogroup viruses. The first one is something called Jamestown Canyon and the second is the Snowshoe hare virus. You know, when you look at clinically, they're all about the same. They cause a very similar type of picture. But those are the main ones that we see in Canada. And collectively we call them arbolviruses or arthropod-borne viruses, something that is spread by a vector like a mosquito.

BRIAN GOLDMAN: For the eastern equine or equine encephalitis, do they call it Triple E, or how do they call it?

DR. SUMON CHAKRABARTI: Yeah, Triple E. And when you denote it on paper as the virus, it's EEEV. Not to be confused with the western equine encephalitis. But the Triple E is the one that we see here.

BRIAN GOLDMAN: Which regions in Canada are most affected?

DR. SUMON CHAKRABARTI: When you look around Canada, you know, you're going to be seeing places where, understandably, mosquitoes are seen most often. Now, you can see that in actually any part of Canada depending on the season. But, you know, we are particularly at risk here in southern Ontario. But, you know, across Canada, anywhere where you can see a lot of mosquitoes. If you've been in Manitoba in the summertime... But, you know, once you start to get a bit more north and it gets cooler, you tend to have less of this type of risk. There are mosquitoes, but they're just not able to have the life cycle that you need in order to be hospitable to these viruses.

BRIAN GOLDMAN: West Nile is the most common mosquito-borne virus. But on average, how many Canadians are we talking about getting infected with the virus each year?

DR. SUMON CHAKRABARTI: So this is highly variable. And, you know, part of this probably has to do with how much we test. But, you know, I do get the sense that when you look back at the records going back as far as 2002, it has really varied. So for example, on average, you know, we're seeing something, more recently, say around 40 to 200 cases -- it's, you know, back and forth. But for example, notably in 2007, we saw 2400 cases across Canada. So, this obviously can be impacted by the testing, the weather, the population of mosquitoes. There's lots of factors. But that's generally what we're seeing over time.

BRIAN GOLDMAN: You know, we use, I gather, indirect methods for figuring out how much West Nile is around, like testing mosquitoes randomly to see if any of them are carrying West Nile. Have I got that right?

DR. SUMON CHAKRABARTI: That's exactly right. And this is something that I've always admired the health authorities for doing, you know, not just for West Nile, but for other things like Lyme. Like tick-trapping and mosquito-trapping surveys just to get an idea of what's out there. The other thing with West Nile that's important is looking at birds. So oftentimes, depending on the area, they'll go out looking for dead birds. Or dead birds that people are reporting and are being tested, so you can get an idea of what the general activity in the community is.

BRIAN GOLDMAN: All right, let's talk about the clinical presentation. What are the main symptoms and signs of West Nile virus?

DR. SUMON CHAKRABARTI: So this is something that I find very interesting, in that much of what we see in the hospital-- that's a lot of the places where West Nile is being diagnosed, is because people are sick enough to come in. So, you know, when you see it in the hospital, it's often people who are coming in with high fevers and particularly headache. So, meningitis. So what I talk about, I ask people to picture the brain like a basketball in a grocery bag. And the grocery bag being inflamed is called meningitis, and when the basketball is inflamed, we call that encephalitis. So, people with meningitis will often have fever, headache, neck stiffness and difficulty looking at lights. And when you get actual encephalitis where the brain itself is inflamed, people have all of that, but also confusion, severe drowsiness, sometimes seizures. So these are kind of the more severe cases. The important thing to note: there's likely a lot of people in the community that actually get West Nile, and it feels like a flu. You get fever, maybe you get a bit of rash, some muscle aches. And it gets better. But that type of person is never sick enough to seek medical attention, let alone get tested for West Nile. So, there likely is a big gradient in the types of cases that we see. But it's important to note the ones that come to light are likely the tip of the iceberg, and they're the most severe ones.

BRIAN GOLDMAN: When West Nile started to move into Canada -- I'm thinking maybe 20 years ago, maybe even a little bit more, maybe even as far away as 25 years ago -- I heard a statistic at one point. It was a rough statistic because the sample size is so small. The idea that maybe for every person who is sick enough to be hospitalized with West Nile virus, there could be 90, 95, even 100 people who either have a mild flu-like illness or no illness at all. Would that still be considered kind of right?

DR. SUMON CHAKRABARTI: Absolutely. And I always take that type of thing with a grain of salt. It was very similar, by the way, with COVID. Is that, what you're seeing, what we-- I call the numerator, is the tip of the iceberg. And then all of these mild cases you never catch are the denominator, plus the sick ones. So, we don't actually know what the denominator is. But I agree with you that the vast majority of the cases are likely mild and never picked up. That's not to take away from the fact that this is something that we should be aware of. It's just that when you look at the broad spectrum of illness, this is likely what the case is.

BRIAN GOLDMAN: And to be clear, there is no specific treatment for West Nile virus, is there? There wasn't 25 years ago, and I don't think there is today, is there?

DR. SUMON CHAKRABARTI: That's correct. It's something that generally you watch and give supportive treatment -- treat the fever, the muscle aches, and in hospital, treat the seizures if they happen. But nothing that specifically can target the virus.

BRIAN GOLDMAN: Have you treated a hospitalized patient with West Nile who required either more invasive monitoring for pressure in the brain, or steroids or other treatment?

DR. SUMON CHAKRABARTI: Absolutely. I've been working in Mississauga for about 15 years or so, and yes, we've definitely seen people. Now, I've also seen people that come in with the not-so-classic case, without the meningitis, but it's somebody who has an unusual fever and they're really sick and it's August. Sometimes I check and I get a hit. But yes, with the more severe cases I've seen a couple. I've seen a few people put in the ICU for seizures. Now, myself, I haven't seen anybody require anything invasive like brain surgery, but certainly that has been described.

BRIAN GOLDMAN: Another mosquito-borne disease that we've been talking about is Triple EV, as you've called it. Eastern equine or equine encephalitis. There are no confirmed cases yet in Canada, but cases have been reported in the northeastern United States, in New England. Why is there so much concern about this particular virus?

DR. SUMON CHAKRABARTI: So this virus, and to be honest about a lot of these infectious diseases, is that, first of all, this is a virus that can spread among horses and other livestock and then occasionally have spillover into humans. And this is something that if somebody gets it and gets sick from it, you can have a significant illness very similar with brain inflammation, which can lead to long-term disability. But the other thing, the other kind of dimension to this is that we are starting to see different infectious diseases presenting in places that you may not have thought of them before. Triple E is one of them. Lyme disease is another, is because of climate change and other types of factors, you're seeing these vectors now thriving in areas they didn't thrive before. And, you know, Canada, we are protected in a certain way because of our winter. But we have seen change over time and these vectors now can potentially thrive in an area they didn't before. We can start to see more cases in Canada. Thankfully, we haven't seen many. If I'm not mistaken, I believe the last human case in Canada was a sporadic one back in 2016. But that said, you know, this could change in the, in the coming years.

BRIAN GOLDMAN: I'm wondering why authorities in New England have raised such public concerns. Are they more concerned that Triple EV is a more serious illness, potentially, than West Nile?

DR. SUMON CHAKRABARTI: Yeah, absolutely. Because the thing about this one is that you do get a significant encephalitis. It's thought that it might have a bit more of a attack rate, so to speak, compared to something like West Nile. But the point is, is that, you know, if you have a virus that can cause encephalitis, which is now going to potentially cause outbreaks in an area, there's always going to be concern. And again, we're seeing that -- we saw an outbreak recently in Massachusetts. Time will tell whether this is something that we're going to see more often, but that's what we were seeing this past summer. Now, I'm not sure if it's changed yet, but they actually for a while had a recommendation to stay in during the dusk hours. So, you know, hopefully that's not going to be forever, but it caused quite a bit of alarm these past couple of weeks.

BRIAN GOLDMAN: So, how concerned should Canadians be about the spread of Triple EV?

DR. SUMON CHAKRABARTI: I think this is something that I call a back-burner kind of concern. I think that-- I'm not seeing any indication that we're going to be seeing an explosion of this. But that said, you know, I suspect in the coming decade we may see more cases as our surveillance is better and these mosquitoes can potentially harbour the virus. So I would say low-level, back-burner type of thing that is not, for example, like the threat right now we're seeing of vaccine-preventable illnesses. That's something I think is more on the forefront that we need to be concerned about now. But for the other ones, this is more of an emerging low-grade thing that I don't think will be at the same level.

BRIAN GOLDMAN: Who's most susceptible to serious illness from contracting these sorts of viruses?

DR. SUMON CHAKRABARTI: This is a very similar thing that we see with other illnesses. So I work with adults, though I can give a little bit of information about children. With adults you're going to see people who are elderly... Actually, I'm not going to give an age cutoff. [indistinct] I don't want to say somebody who's over 65 is elderly. But I mean that, 65 and older, especially people in their 80s, people who have immune-compromising conditions such as cancer, chemotherapy, transplant -- these individuals are those who are higher risk of contracting the illness because the immune system doesn't stop it, but also at risk of having more severe illness. Another one to consider are young children -- the extremes of age. Like, I'm talking about, you know, newborns, infants. This is a very similar theme that you see with any other type of illness that we encounter.

BRIAN GOLDMAN: And certainly, we heard in the news about Dr. Anthony Fauci being hospitalized with West Nile virus. He's certainly over the age of 80. I don't know what his other medical illnesses are and I'm not sure that that's our business, but, you know, at least from the standpoint of age, that placed him in a higher risk category.

DR. SUMON CHAKRABARTI: And again, you know, when we heard this news, I wish nothing but a speedy recovery from him. But yes, he would be someone that... You know, and again, I do say that risk factors are additive. So, you know, the age is one, but for example, somebody who is over 80 and has something else like advanced COPD or something like that. Active cancer. These are things... I agree, I don't know what his health history is, but he at least has that as a risk factor.

BRIAN GOLDMAN: One thing I wanted to ask you about the situation in New England. We heard that a New Hampshire man was infected with three mosquito-borne diseases at the same time. You know, according to the news reports, he was fighting for his life. And I'm wondering, what might multiple mosquito-borne infections at one time do to us?

DR. SUMON CHAKRABARTI: The idea that it would make you more sick is certainly justified. One interesting thing, though, is -- and I mentioned this with COVID as well -- is our body is very, very good at dealing with viruses. And one interesting response that we have is, in general, when you get infected with a virus, you get this general anti-viral type of response where you're specifically targeting the virus that's infecting you, but your body has also made the environment inhospitable to viral growth, which can potentially reduce the growth of other viruses that you're being exposed to. So, I would rather not get infected with any virus -- I think I speak for most people in that regard -- but our body does have defense for that. But again, co-infections are not unheard of. We certainly see that with other infections as well. This is certainly an area that we are going to be looking into more and more in the coming years.

BRIAN GOLDMAN: Sumon, you touched on climate change and I think it's worth elaborating on that, talking about how climate change is influencing the spread of mosquito-borne diseases in North America.

DR. SUMON CHAKRABARTI: This is something that goes far beyond just West Nile. Just to give an example, I trained at the University of Toronto back in, you know, around 2008 to '10 when I was a fellow. And at that time we were talking about something like chikungunya, which is another mosquito-borne virus, coming into the West. And, you know, at that time we thought, no, it's not possible. But, you know, I was thinking, look, we're seeing these vectors coming from areas. We're seeing the climate now supporting the... maybe a, say, prolonged activity, prolonged life cycle of these previously not seen vectors. And would you know it, we saw a chikungunya outbreak, we saw a Zika outbreak in an area where we didn't see it before. More local into Canada, I think the one thing is Lyme. We're seeing that these ticks are now in areas that we never saw them 15, 20 years ago. And I personally have seen tremendous number of Lyme cases in these past five years that I didn't see before. So, climate change is certainly a factor here for the vectors' encroachment of the natural habitats where humans are now living closer to these areas. So, there's a lot of factors involved, but definitely climate change and infectious diseases have a intimate type of relationship.

BRIAN GOLDMAN: The main mosquito vector for West Nile is Aedes aegypti. And it's not going to be able to overwinter in Canada -- and I believe that that's the expression. But as our spring and fall seasons get warmer and longer, that affords a greater opportunity for mosquitoes such as Aedes aegypti that happen to arrive in Canada, to have multiple breeding cycles. And that can increase the risk of West Nile proliferating.

DR. SUMON CHAKRABARTI: And let's not forget that even if we take climate change out of the picture, West Nile has been here. This is a virus that was initially described in Uganda back in, you know, the late '30s -- which is obviously a tropical climate -- and it has been able to persist here in Canada because you can have prolonged infections in birds, who can then spread it to the mosquitoes in the spring. And I agree with you that if you are having a longer spring, this does give further opportunity for these infected mosquitoes to bite humans and increase the potential for disease.

BRIAN GOLDMAN: Last question I want to ask you. There's no vaccine for diseases like West Nile virus or Triple EV, so how can we protect ourselves?

DR. SUMON CHAKRABARTI: Much of the protection that we have comes from avoiding the bite of mosquitoes. So for personal protection, I understand it's not always going to be pragmatic, especially when it's really hot outside. But things like wearing long sleeves, long pants when you're outside. Colours that aren't too bright that attract mosquitoes. And of course, using things like mosquito repellent. These things are all things that can help. From the environmental standpoint, mosquitoes love standing water, so try to get rid of that around the house. Whether that's, you know, a dog bowl with water in it, standing water from a puddle, old tires. This type of thing. And then there is also just avoidance of the peak biting times, which is generally for these types of mosquitoes -- Culex in Canada -- is from dawn to dusk. And dawn and dusk particularly, as anybody who lives in Canada knows, that during the evening is when you get bitten the most. Not being outside during those times. These are things that we can do to protect ourselves. It's not always going to be 100% effective, but just remember one thing, is that, you know, we've all been living with mosquito bites for years. And in general, this is a rare infection. So even just doing that little bit, takes a rare infection and it can hopefully reduce the risk to make it even rarer.

BRIAN GOLDMAN: Dr. Sumon Chakrabarti, thank you so much for speaking with us once again on The Dose.

DR. SUMON CHAKRABARTI: Always great to be here. Thank you so much for having me.

BRIAN GOLDMAN: Dr. Sumon Chakrabarti is an infectious diseases specialist with Trillium Health Partners in Mississauga, Ontario. Here's your dose of smart advice: In Canada, West Nile virus is the most common virus carried by mosquitoes. Others found in Canada include eastern equine encephalitis, Triple EV, Saint Louis encephalitis and California serogroup viruses. Mosquitoes get infected with viral illnesses by feeding off the blood of infected animals such as wild birds, deer, horses, sheep, and rodents. Once infected, the mosquitoes transmit viruses to humans through mosquito bites. The symptoms of these infections usually begin a few days to two weeks following a bite. They include fever, headache, fatigue, nausea, vomiting, and rash. Many people who are infected have no symptoms, but some get seriously ill with encephalitis, or inflammation of the brain; meningitis or inflammation of the lining of the brain and spinal cord; or myelitis, which affects the spinal cord. Severe cases of Triple EV progress from initial flu-like symptoms to disorientation, seizures, encephalitis, and coma. There are no vaccines or antibiotics for mosquito-borne viruses. You treat the symptoms by getting plenty of rest, fluids and by treating aches and pains and fever with over-the-counter medicines. Serious conditions like meningitis and encephalitis may require hospitalization. Avoiding mosquitoes is the surest way to prevent infection. Wear protective clothing, use insect repellent, and stay indoors at dawn and dusk when mosquitoes are most active. And keep your environment free from mosquitoes. That means getting rid of any standing water where mosquitoes can breed. Climate change means mosquito-borne diseases have increased over the past 20 years. It's something we'll increasingly need to follow. If you have topics you'd like discussed or questions answered, our email address is thedose@cbc.ca. If you like this episode, please give us a rating and review wherever you listen. This edition of The Dose was produced by Sameer Chhabra. Our senior producer is Colleen Ross. The Dose wants you to be better informed about your health. If you're looking for medical advice, see your health-care provider. I'm Dr. Brian Goldman. Until your next dose.

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Why should I be concerned about mosquitoes? - Transcript

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