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Showing posts with label mosquitoes. Show all posts
Showing posts with label mosquitoes. Show all posts

Thursday, September 21, 2023

How warmer climates spread disease; Fighting dengue with more mosquitoes

 

A mosquito feeds at the Salt Lake City Mosquito Abatement District in Salt Lake City, United States.-AP


How warmer climates spread disease


LIVING on the edge of wetlands on the Italian island of Sardinia, Anna Rita Cocco is mourning the loss of her elderly father who died in a coma within weeks of a fatal mosquito bite.

“My father was full of life and used to walk for miles each day. I was expecting him to die at some point, but not suffering like that, taken from me by a mosquito,” she said her late father, Bernardino, who died aged 80.

Italy was only declared malaria-free by the World Health Organisation (WHO) in 1970, but now, other lesser-known mosquito- or tick-borne diseases are on the rise.

A complex mix of global warming, changes in land use and more movement of people and goods are contributing to the spread of illnesses – such as dengue or Lyme disease – to new regions in a worsening trend, the UN panel of scientists says.

Migratory birds infected by mosquitoes and flying over 3,200km from Senegal in West Africa have been identified as carriers of the West Nile virus that killed Cocco’s father in Sardinia, where summers are becoming hotter.

The Mediterranean island, and northern areas of Italy where the virus is also spreading, are both suffering more extreme events of floods and droughts.

Abundant water helps mosquitoes to breed, while more drought and fewer trees constrict the migratory birds’ ecosystems, forcing them into closer contact with each other, enabling some diseases to spread.


A municipal worker fumigates a housing colony as a preventive measure against mosquito-borne diseases in Hyderabad, India. —AFP

“People don’t seem to be aware of the threat,” said Cocco.

Epidemiologists identify habitat change as one of the main factors behind the intercontinental leap of the West Nile virus.

First identified in 1937 in the West Nile region of Uganda, the disease has spread within Africa and to other continents. Almost 3,000 people have died in the United States alone since a first outbreak in New York in 1999.

In the red clay houses of Maka Diama village in northwest Senegal, women make soap from plants that grow in a nearby river, which they sell to tourists and local hotels, and cook rice grown in surrounding paddy fields.

Recent years have seen huge changes in this wetland region teeming with crocodiles and migratory birds, most notably a leap in rice production, driven by government efforts to reduce Senegal’s reliance on imported rice.

Barrages built near the coast to retain and safeguard freshwater supplies from salty sea water have slowed river flows, and fertilisers used for rice paddies have encouraged the growth of river plants.

This push for greater food self-sufficiency has tripled rice production to 1.3 million tonnes over a decade. But changes in land use have upset the delicate wetland habitats, helping mosquitoes which lay eggs in stagnant water.

“There are so many mosquitoes here these days,” said Arame Diop, one of the village soap-makers. “Far more than there used to be.” Diop’s family already sleeps under mosquito nets to avoid malaria, which is endemic in Senegal.

Assane Gueye Fall, an entomologist at the National Livestock and Veterinary Research Laboratory in the capital, Dakar, said Senegal’s policies sought to improve food and water security.

“But to solve a problem, they created another,” he said of what he called the “explosion of mosquitoes” and of disease.

The long-distance carriers of West Nile are birds that receive the virus from bites by infected mosquitoes and then fly on their migratory routes, to be bitten once more by mosquitoes that then spread illness to people and other animals, mainly horses. Flamingos, herons, storks and birds of prey are among many migratory species found in the wetlands of the Djoudj National Bird Sanctuary, a Unesco World Heritage Site near Maka Diama.

Navigating his boat slowly, captain Ibrahima Ndao, the park conservationist, explained how abrupt changes in land use are impacting the wetlands. Pelicans are swooping all around, catching fish for their young.

“There has been a significant expansion of paddy fields around the reservoir. But we have to make sure that the birds’ environment is preserved,” he said.

“If the space of their environment is reduced, it’s easier for illnesses to spread,” said Ndao, pointing out increased growth of plants along the banks, including those used by the women of Maka Diama to make soap.

Ndao stressed the importance of a “one-health approach” that looks at human and animal health as one issue.

As in Europe, Senegal is also losing natural habitats through desertification exacerbated by climate change, forcing animals into closer contact with human communities. Vector-borne diseases – such as malaria, dengue, Zika, yellow fever and West Nile – are seen by WHO as an increased threat in Africa, potentially affecting over 800 million people, some 70% of the population.

West Nile virus has gained a foothold in an increasing number of countries, from Australia to Venezuela. Because it is easy to confuse West Nile with a generic flu or other mosquito-borne illnesses, patients rarely get tested. As a result, the impact of the virus in Africa is virtually unknown.

West Nile is often asymptomatic or mild, but one out of 150 people who contract the virus can develop severe neurological complication including meningitis, paralysis and even death.

In 2022, 12 European nations reported 1,335 locally acquired cases of West Nile virus – with a few others brought in by international travellers – and 104 deaths. It was the highest number of cases since a peak of more than 1,500 in 2018.

Italy suffered most in the European Union in 2022 with 51 deaths, ahead of 33 in Greece and five in Romania, according to the European Centre for Disease Prevention and Control. A public health campaign is alerting people, and authorities are stepping up tests of birds and mosquitoes.

The main vector is the Culex mosquito, but what makes West Nile potentially endemic is that it can be transmitted by more than 50 species of mosquito and by ticks, said entomologist Fall in Dakar. By contrast, dengue, for example, relies on one or two species. — Reuters

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Fighting dengue with more mosquitoes


Boquín, a project leader working with Doctors Without Borders, holding a glass jar filled with mosquitoes before their release in neighbourhoods rife with dengue, in a facility in Tegucigalpa. Doctors Without Borders is partnering with the World Mosquito Programme to release close to nine million Wolbachia-infected mosquitoes in Tegucigalpa over the next six months. —AP


FOR decades, preventing dengue fever in Honduras has meant teaching people to fear mosquitoes and avoid their bites. Now, Hondurans are being educated about a potentially more effective way to control the disease – and it goes against everything they’ve learned.

Which explains why a dozen people cheered last month as Tegucigalpa resident Hector Enriquez held a glass jar filled with mosquitoes above his head, and then freed the buzzing insects into the air.

Enriquez, a 52-year-old mason, had volunteered to help publicise a plan to suppress dengue by releasing millions of special mosquitoes in the Honduran capital, Tegucigalpa.

The mosquitoes Enriquez unleashed in his El Manchen neighbourhood – an area rife with dengue – were bred by scientists to carry bacteria called Wolbachia that interrupt transmission of the disease. When these mosquitoes reproduce, they pass the bacteria to their offspring, reducing future outbreaks.

This emerging strategy for battling dengue was pioneered over the last decade by the non-profit World Mosquito Programme, and it is being tested in more than a dozen countries. With more than half the world’s population at risk of contracting dengue, the World Health Organisation is paying close attention to the mosquito releases in Honduras, and elsewhere, and it is poised to promote the strategy globally.

In Honduras, where 10,000 people are known to be sickened by dengue each year, Doctors Without Borders is partnering with the mosquito programme over the next six months to release close to nine million mosquitoes carrying the Wolbachia bacteria.

“There is a desperate need for new approaches,” said Scott O’Neill, founder of the mosquito programme.


A Doctors Without Borders’ worker releasing laboratory-bred mosquitoes infected with bacteria that interrupt the transmission of dengue, in Tegucigalpa, Honduras, where 10,000 people are known to be ill from dengue each year. — AP

Scientists have made great strides in recent decades in reducing the threat of infectious diseases, including mosquito-borne viruses like malaria. But dengue is the exception: its rate of infection keeps going up.

Models estimate that around 400 million people across some 130 countries are infected each year with dengue. Mortality rates from dengue are low – an estimated 40,000 people die each year from it – but outbreaks can overwhelm health systems and force many people to miss work or school.

“When you come down with a case of dengue fever, it’s often akin to getting the worst case of influenza you can imagine,” said Conor McMeniman, a mosquito researcher at Johns Hopkins University. It’s commonly known as “breakbone fever” for a reason, McMeniman said.

Traditional methods of preventing mosquito-borne illnesses haven’t been nearly as effective against dengue.

The Aedes aegypti mosquitoes that most commonly spread dengue have been resistant to insecticides, which have fleeting results even in the best-case scenario. And because dengue virus comes in four different forms, it is harder to control through vaccines.

Aedes aegypti mosquitoes are also a challenging foe because they are most active during the day – meaning that’s when they bite – so bed nets aren’t much help against them. Because these mosquitoes thrive in warm and wet environments, and in dense cities, climate change and urbanisation are expected to make the fight against dengue even harder.

“We need better tools,” said Raman Velayudhan, a researcher from the WHO’s Global Neglected Tropical Diseases Programme. “Wolbachia is definitely a long-term, sustainable solution.”

Velayudhan and other experts from the WHO plan to publish a recommendation to promote further testing of the Wolbachia strategy in other parts of the world.

The Wolbachia strategy has been decades in the making.

The bacteria exist naturally in about 60% of insect species, just not in the Aedes aegypti mosquito.

“We worked for years on this,” said O’Neill, 61, who with help from his students in Australia eventually figured out how to transfer the bacteria from fruit flies into Aedes aegypti mosquito embryos by using microscopic glass needles.

Around 40 years ago, scientists aimed to use Wolbachia in a different way: to drive down mosquito populations. Because male mosquitoes carrying the bacteria only produce offspring with females that also have it, scientists would release infected male mosquitoes into the wild to breed with uninfected females, whose eggs would not hatch.

But along the way, O’Neill’s team made a surprising discovery: mosquitoes carrying Wolbachia didn’t spread dengue – or other related diseases, including yellow fever, Zika and chikungunya.

And since infected females pass Wolbachia to their offspring, they will eventually “replace” a local mosquito population with one that carries the virus-blocking bacteria.

The replacement strategy has required a major shift in thinking about mosquito control, said Oliver Brady, an epidemiologist at the London School of Hygiene and Tropical Medicine.

“Everything in the past has been about killing mosquitoes, or at the very least, preventing mosquitoes from biting humans,” Brady said.

Since O’Neill’s lab first tested the replacement strategy in Australia in 2011, the World Mosquito Programme has run trials affecting 11 million people across 14 countries, including Brazil, Mexico, Colombia, Fiji and Vietnam.

The results are promising. In 2019, a large-scale field trial in Indonesia showed a 76% drop in reported dengue cases after Wolbachia-infected mosquitoes were released.

Still, questions remain about whether the replacement strategy will be effective – and cost effective – on a global scale, O’Neill said. The three-year Tegucigalpa trial will cost US$900,000 (RM4.2mil) , or roughly US$10 (RM46) per person that Doctors Without Borders expects it to protect.

Scientists aren’t yet sure how Wolbachia actually blocks viral transmission. And it isn’t clear whether the bacteria will work equally well against all strains of the virus, or if some strains might become resistant over time, said Bobby Reiner, a mosquito researcher at the University of Washington.

“It’s certainly not a one-and-done fix, forever guaranteed,” Reiner said.

Many of the world’s mosquitoes infected with Wolbachia were hatched in a warehouse in Medellín, Colombia, where the World Mosquito Programme runs a factory that breeds 30 million of them per week.

The factory imports dried mosquito eggs from different parts of the world to ensure the specially bred mosquitoes it eventually releases will have similar qualities to local populations, including resistance to insecticides, said Edgard Boquín, one of the Honduras project leaders working for Doctors Without Borders.

The dried eggs are placed in water with powdered food. Once they hatch, they are allowed to breed with the “mother colony” – a lineage that carries Wolbachia and is made up of more females than males.

A constant buzz fills the room where the insects mate in cube-shaped cages made of mosquito nets. Caretakers ensure they have the best diet: males get sugared water, while females “bite” into pouches of human blood kept at 37°C.

“We have the perfect conditions,” the factory’s coordinator, Marlene Salazar, said.

Once workers confirm that the new mosquitoes carry Wolbachia, their eggs are dried and filled into pill-like capsules to be sent off to release sites.

The Doctors Without Borders team in Honduras recently went door-to-door in a hilly neighbourhood of Tegucigalpa to enlist residents’ help in incubating mosquito eggs bred in the Medellin factory.

At half a dozen houses, they received permission to hang from tree branches glass jars containing water and a mosquito egg-filled capsule.

After about 10 days, the mosquitoes would hatch and fly off.

That same day, a dozen young workers from Doctors Without Borders fanned out across Northern Tegucigalpa on motorcycles carrying jars of the already hatched dengue-fighting mosquitoes and, at designated sites, released thousands of them into the breeze.

Because community engagement is key to the programme’s success, doctors and volunteers have spent the past six months educating neighbourhood leaders, including influential gang members, to get their permission to work in areas under their control.

Some of the most common questions from the community were about whether Wolbachia would harm people or the environment. Workers explained that any bites from the special mosquitoes or their offspring were harmless. — AP

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Fighting dengue mosquito with Wolbachia


Everyone must do their part as the number of dengue cases this year projected to break a new record


Dengue case numbers to peak this year following cycle uptrend

 


Monday, September 18, 2023

Everyone must do their part as the number of dengue cases this year projected to break a new record


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PETALING JAYA: With the number of dengue cases this year projected to break a new record, health experts say a whole of society approach is what it takes to contain the surge.

They said piecemeal strategies such as fogging or mosquitoes with Wolbachia are not enough to stem an outbreak, and that it is the combination of methods that will save lives.

Time is also of the essence as there are already 59 deaths due to dengue logged this year from January to Sept 9, compared with 56 deaths for the whole of 2022.

There were also 82,485 cases from January to Sept 9, 2023, compared with the 66,102 cases in 2022.


Asia Dengue Voice and Action Group international adviser Prof Dr Tikki Pangestu (pic) said integrated efforts are needed to fight dengue not just by deploying mosquitoes infected with Wolbachia, or vaccines.

Countries at the recent 6th Asia Dengue Summit in Bangkok, Thailand, agreed that what is needed is an integrated holistic set of strategies and initiatives that has five key components, he added.

“The first one is straightforward – surveillance. That’s basically tracking and keeping tabs on viruses, on a number of cases, on the number of mosquitoes,” he said in an interview.

“Secondly, the health system must be ready to manage those who actually get sick with dengue and end up in hospital.

“About 90% of people who get dengue do not need to go to hospital. They can maybe go and see a GP (general practitioner), rest at home and that’s fine.”

“But for the serious cases, hospitals need to be ready to manage and take care of them,” said Prof Pangestu, who is a visiting professor at the Yong Loo Lin School of Medicine, National University of Singapore.

It is only then that vector control measures and vaccines can play a role, he added.

“But the fifth and final one, which is perhaps the most important in terms of a foundational stone behind all the other strategies, is community involvement.

“Community engagement, community buy-in, and community awareness of the dangers of dengue – that is the fifth column.

“It involves community education and community awareness so that in their everyday lives, they make sure that their immediate environment does not encourage mosquito breeding,” said Prof Pangestu.

Another expert, Dr Rahmat Dapari, said the projected outbreak later this year or next year could potentially surpass the historic number of cases in the 2019 outbreak.

Over 130,000 dengue cases were recorded in 2019, beating the previous historic high of 120,836 cases reported for the whole of 2015, said Dr Rahmat of Universiti Putra Malaysia.

But there were fewer deaths in 2019 at 182, compared with 336 in 2015, said the senior medical lecturer and public health medicine specialist.

Dr Rahmat said while various vector control measures have been implemented to reduce disease transmission, including the destruction of mosquito breeding places, fogging, community clean-ups and health education, these methods alone were not sufficient.

Innovations such as Wolbachia-infected mosquitoes and dengue vaccination are promising but there is still a need for communities to do their part, he added.

Wolbachia is a bacterium and a form of biological control that is naturally occurring in 60%-70% of insects, spiders and nematodes.

Selected strains of Wolbachia have been introduced into Aedes aegypti populations to prevent transmission of dengue viruses by the vector.

Currently, the Health Ministry has deployed Wolbachia-carrying Aedes in 28 localities in Malaysia.

“To this end, there needs to be a holistic approach using varied strategies so that dengue can be tackled from every angle.

“This involves collaboration between multiple agencies and different fields of expertise, as well as community engagement and education, together with diverse strategies that address breeding and transmission, and preventive methods,” said Dr Rahmat.

He added that the newly established Dengue Prevention Advocacy Malaysia (DPAM) also plays a crucial role in supporting the government to foster holistic dengue management strategies and reduce resource burdens.

“As a community, we must be well informed of these novel approaches and be more disciplined and proactive in doing our part to support the government in combating dengue.

“By working together, we can make a significant impact and create a safer and healthier environment for all Malaysians,” he said.

Tropical Infectious Diseases Research and Education Centre director Prof Dr Sazaly Abu Bakar said while the number of dengue cases in 2023 may seem high, it is not even half of the cases during pre-pandemic times such as in 2019.

“There must be a full and total commitment by the government to tackle dengue and not just leave it to the Health Ministry,” he said.

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Dengue case numbers to peak this year following cycle uptrend

 

Tuesday, April 11, 2023

Fighting dengue mosquito with Wolbachia

 

How do male Wolbachia-Aedes mosquitoes help suppress dengue mosquito population?

 

 Prof Ooi Eng Eong on using Wolbachia-Aedes mosquitoes to control dengue

Wolbachia mosquitoes have been released in some 39 localities since the “successful” pilot run of a dengue control project in 2017 that significantly reduced cases, according to the Institute for Medical Research (IMR).

The IMR, which is the research arm of the Health Ministry, told The Star that the Malaysian Wolbachia project that was launched on March 28, 2017, saw Wolbachia-carrying Aedes mosquitoes being released at 11 dengue hotspots in the Klang Valley.

“After one year of release, dengue cases decreased significantly,” it said.

IMR said that “after seeing the promising effect of the initial releases and being impressed by the apparent success of the trial”, the Health Ministry’s Disease Control Department, in collaboration with the IMR, has deployed Wolbachia-carrying Aedes to 28 more localities.

“The outcomes of this operational programme serve as the basis for future expansion of releases in additional dengue-prone areas.

“Malaysia is the first endemic country to use Wolbachia mosquitoes for dengue control. The Health Ministry has established a five-year plan for the release of Wolbachia mosquitoes in dengue hotspots as its rollout programme,” it said.

Vector control, consisting of source reduction, chemical control, biological control, and even genetic control, was one of the strategies used to combat Aedes-borne viruses, IMR said.

Biological control consists of using Wolbachia mosquitoes and the “sterile insect technique”.

“The Malaysian approach is a replacement strategy, where both male and female mosquitoes are released to replace the wild Aedes population in the field,” IMR said.

In other words, the “bad” Aedes aegypti mosquitoes are replaced with “good” Aedes aegypti mosquitoes.

The female Aedes aegypti mosquitoes carrying Wolbachia prevent the growth of dengue virus in the mosquitoes so that the dengue virus could not be transmitted when mosquitoes bite humans, it added.

IMR said the added benefit of the Wolbachia strategy was that it prevented the mosquito from picking up dengue virus from dengue patients who are asymptomatic.

“The asymptomatic transmission of dengue virus to mosquitoes through mosquito bites has been known for years, but there has been no solution to prevent it, but with the Wolbachia strategy, the solution is there,” it said.

When contacted last month, Health director-general Tan Sri Noor Hisham Abdullah said that analysis had shown that dengue cases had been reduced by 75% to 100% in the 14 localities where the Wolbachia Mosquito Operation (WMO) had been implemented for at least two years.

“Nevertheless, ongoing evaluation is required to assess the effectiveness of WMO in reducing dengue cases as well as its impact on averting dengue morbidity and mortality in the long term,” he said.

He said the WMO, which was launched in 2019, had also become a novel tool for vector control under the National Dengue Control and Prevention Programme.

Since July 2019, 28 high-dengue burden localities in Selangor (10), Kuala Lumpur and Putrajaya (7), Penang (4), Kelantan (2), Johor (2), Pahang (2), and Melaka (1) have been selected to implement WMO in a staggered manner.

Wolbachia is a bacterium and a form of biological control that is naturally occurring in 60%-70% of insects, spiders and nematodes.

It is usually introduced into Aedes mosquitoes to prevent the transmission of dengue viruses.

The Wolbachia bacteria stops the dengue virus from replicating, so the mosquito does not spread the virus when it bites. 

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Friday, March 31, 2023

Dengue case numbers to peak this year following cycle uptrend

 



Dengue spike due to four-year epidemic cyclical pattern, says Health DG

 

PETALING JAYA: The rising number of dengue cases is part of a cyclical trend and is expected to peak this year, says Tan Sri Dr Noor Hisham Abdullah.

The Health director-general said this was based on national data, which shows that dengue trends follow a cyclical pattern with an epidemic being reported every four to five years.

“The recent dengue epidemics were observed in 2014 and 2019, with an average of 2,300 cases per week and 2,500 cases per week reported respectively.

“The rising number of dengue cases is partly contributed by the change in dominant circulating dengue serotype, or the ‘serotype shift’, which is a well-known reason for dengue surges.

“It has been observed that dengue cases will increase usually four to six months after a serotype shift due to the lack of immunity in the community towards the new dominant circulating serotype,” he said in a statement yesterday.

From the Health Ministry’s surveillance monitoring, there has been a shift of the circulating dengue virus serotype from DEN 3 to DEN 4 since June 2021, Dr Noor Hisham added.

Since then, the DEN4 serotype has been the dominant circulating virus serotype in the environment, he said.

In 2022, Malaysia reported 66,102 dengue cases with 56 deaths, compared to 26,365 cases with 20 deaths in 2021.

This was an increase of 150.7% in dengue cases and a 180% increase in deaths from the previous year.

Dr Noor Hisham said that other countries in the region are also seeing a rise in dengue this year.

In terms of contributing factors, he pointed out that human behaviour, such as littering, is among the main reasons for poor environmental cleanliness.

“The abundance of man-made containers (being littered) have provided suitable breeding places for Aedes mosquitoes,” he said, adding that climatic change is also an important factor, especially with alternating rainy and hot seasons. 

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