Moorland mosquitoes: How new diseases could spread

DW (English)

In Germany’s Peene Valley wetlands, researchers are looking at what rewetting means for local mosquito populations – especially in species that transmit viruses and parasites.

Transcript

00:00Are there health hazards lurking in these wetlands?

00:08Let's track down the facts with the help of these two scientists.

00:12On a trip to trap mosquitoes in the wild.

00:16How do you catch the tiny pests for research?

00:19What health threats do they pose?

00:21And why are they given blood to feast on in the lab?

00:27We joined the hunt.

00:31It took us into the Peene Valley wetlands in northeastern Germany.

00:35They were once drained to create farmland,

00:37but over the last 30 years or so,

00:39unused areas have been re-wetted,

00:42allowing the bogs to make a comeback.

00:45Meet our two researchers.

00:47Mandy Schaefer and Patrick Gutier work at Germany's Federal Authority for Animal Health,

00:52the Friedrich-Loeffler-Institute.

00:55It's a beautiful day.

00:58Although trudging through this terrain can be challenging.

01:01Should we be worried about being swallowed up by the bog?

01:05You rarely sink deeper than either your waist or your chest.

01:09And, of course, that's sort of a shock to people,

01:14but you cannot drown in a peeple.

01:16Some areas are so springy you can bounce up and down on them like a waterbed.

01:21In damp environments like this, mosquitoes are never far away,

01:25and they can carry a range of disease-causing pathogens.

01:29We want to find out whether re-wetting peatlands or other types of land

01:35changes the makeup of the mosquito population,

01:39and whether we can find strategies for influencing that change,

01:43in order to disarm potential dangers to humans and animals.

01:47People like Rezi Scheumann and animals like her cow Uschi, but more on them later.

02:00We pass a spot in the peatland that draws an enthusiastic story from Patrick.

02:07This is the site where we found specimen 323,

02:10our first specimen from the species Uranotainia unguiculata,

02:14which is a relatively rare species in Germany,

02:17and we didn't expect to find it here at first.

02:19This is the most northerly spot it's been found.

02:22It normally inhabits areas around the Mediterranean.

02:25Uranotainia unguiculata is one of around 4,000 mosquito species worldwide.

02:32Another is Culex pipiens, which is native to Germany.

02:36It can carry and transmit West Nile virus, which mostly infects birds,

02:40but less often horses or humans.

02:45Culacita morsitans is also found in the northern hemisphere.

02:48In North America, it's been shown to carry the eastern equine encephalitis virus,

02:53which causes a disease that can be potentially lethal for horses.

03:00Then there's Aedes albopictus.

03:02The Asian tiger mosquito, which used to be restricted largely to that continent,

03:06is now also in Europe.

03:08And it can transmit the Zika, chikangunya and dengue viruses.

03:12And finally, this species can transmit Plasmodia, parasites that cause malaria.

03:18But to do so it needs human hosts, and Germany is officially malaria-free.

03:23So does Anopheles clavager pose a threat?

03:27They can still be found in Germany, and can theoretically transmit malaria pathogens.

03:33Although our healthcare system is so well developed that cases of malaria are identified quickly,

03:40and local transmission is rare.

03:45And this is how scientists hunt down and capture mosquitoes.

03:49They use special traps containing carbon dioxide to simulate air exhaled by potential mosquito targets.

03:55The insects also like certain body odors.

04:00There's a chemical attractant in the trap.

04:04The chemical scent has an intense, sweaty smell that attracts various types of mosquitoes,

04:10especially those that target mammals.

04:15I wouldn't say it stinks.

04:17It has a particular composition that loses specific types of mosquito.

04:23The trap is activated.

04:25In 24 hours the researchers will collect their whole of mosquitoes.

04:29Today is a tough Boglins log.

04:35Plenty of water improves the chances of finding mosquito breeding grounds,

04:40which in turn indicates which species prefer which habitats.

04:43See that little black line twitching around?

04:48You can tell it's an Anopheles larva from how it lies parallel to the surface.

04:53It doesn't have an air tube in back.

04:55Air tube?

04:57It's found on the insect's tail, a kind of siphon that supplies growing mosquitoes with oxygen from the surface.

05:04It's essentially a snorkel.

05:06Like the adults that end up in the trap, the mosquito larvae will end up in the lab,

05:11but hold on, let's back up a little.

05:15This is no ordinary lab.

05:20This is the Friedrich-Loeffler-Institut on the island of Riems on Germany's Baltic Sea coast.

05:26Research conducted here is focused on animal health,

05:29from nutrition to epidemics and infectious diseases in livestock.

05:33Before entering the insectarium, we have to strip naked and change into special clothes.

05:39In the lab, biosafety level 2 rules apply.

05:43Then there's a negative pressure airlock.

05:46So when the door opens, nothing can fly out.

05:49But back to our mosquito larvae.

05:51After collection, we put them in these incubators to maintain more or less natural conditions,

05:58to rear them from their sub-adult stages to their adult stages.

06:02After hatching from eggs, mosquitoes go through four stages of larval development in the water before pupating.

06:13They only leave their watery environment when the adults emerge from the pupa.

06:20Catching individual specimens in the lab can be pretty tricky.

06:23The way this works is that you try to collect all the mosquitoes in the upper part of this net.

06:33And if they don't play along, we'll extend the entire setup.

06:37The toilsome larva hunting in the boglands, then rearing them in the lab and harvesting the adults with some technical ingenuity,

06:52it's all just prep work for the actual research.

06:54We breed mosquitoes for a variety of studies.

07:00In some of them we test the vector competence of different species.

07:04Vector competence is the ability of mosquitoes or other arthropods to transmit pathogens.

07:10This involves producing them in large numbers so that we have enough for experiments.

07:16We use vector competence trials to test whether certain mosquito species can transmit specific pathogens.

07:25Patrick Gutjahr is preparing to feed his little charges some blood.

07:29There are no host animals in the insectarium for the mosquitoes to dine on,

07:33but after mating, the females need blood to produce eggs and therefore have to be fed.

07:40This blood was taken from cattle.

07:43Depending on the species, mosquitoes prefer different hosts, which might be amphibians, birds or, well, mammals like us.

07:54Back to the mosquito hunt, and a pumping station where the researchers have also set a trap.

08:01Mandy Schaefer and Patrick Gutjahr have put out 15 in all, in both wet and dry peatlands.

08:07Dry peatlands are areas that are still drained for agricultural use.

08:18As it has for centuries, farming plays an important role here.

08:21Though livestock numbers have dropped steadily in the region,

08:24there is still a lot of contact between humans and animals.

08:26A long time ago, there used to be a lot of mosquitoes here.

08:36Uschi was covered in them.

08:39It was awful.

08:40Milking her was unbearable.

08:43So I went and rubbed mosquito repellent into her.

08:48Which did help a bit.

08:52Right, Uschi?

08:54There is a mosquito trap in Resi Scheumann's garden, too.

08:58If re-wetting peatlands means more of the insects, locals will also obviously be affected.

09:04Although the importance of the scientific findings extends well beyond the region.

09:08It's always important to check for specific details that are affecting the area first,

09:15and then gradually zoom out and see what global or general patterns we may find in mosquito behaviour,

09:23and also in pathogen transmission cycles.

09:25The inquisitive researchers check the rainwater barrels.

09:30This time, their curiosity pays off. It's full of larvae.

09:34It's good they check. They have to know how many foreign mosquitoes we have around here.

09:42Identifying the species of mosquitoes later is a very laborious undertaking.

09:48To date, Patrick Gutier has analysed 114,000 specimens, and there are 20,000 more in the freezer still waiting to be examined.

09:59The researchers identify species by looking at morphological features, such as particular scale patterns,

10:06or how long leg segments are in relation to each other.

10:11If need be, they turn to what's called DNA barcoding, where species are determined based on a specific genetic sequence.

10:18But the researchers can identify many species by eye alone.

10:26This is an Anulipes.

10:28Anulipes.

10:29And right behind it, what looks like a clavager with a white stripe.

10:37And a mohawk too.

10:40And another clavager.

10:46Aedes loycomelas.

10:51Right.

10:53Patrick reveals one delicate method of examination.

10:57It's relatively common in entomology to take off the male genitalia and prepare them as a microscopic sample, basically.

11:09And then look at the really fine structures to determine the species.

11:14They are also on the lookout for invasive species.

11:17Aedes albopictus, which, as mentioned, is native to the Asia-Pacific region, has made its way to Europe.

11:23Until now, though, it's mostly been found in southern and western Germany.

11:29Finding Aedes albopictus here in northeast Germany would be a first.

11:33It would tell us that the species is spreading and that we need to track that.

11:40This species has a relatively broad vector competence.

11:44It can transmit a range of pathogens effectively.

11:47And that's the kind of information that's relevant in an outbreak context, for example.

11:57The researchers have found close to 30 types of mosquito in the Peene Valley peatlands.

12:03But so far, none pose an immediate danger to humans.

12:07A happy end to our tale of mosquitoes.

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