How Jamaica plans to fight Dengue with Sterilized male Aedes aegypti mosquitoes

“We are projecting to start releasing by March 2020. We have about a million in the lab. If you go there now, you would witness the mosquitoes going through the processes. We keep them in cages and feed them on human blood from the Blood Bank and other blood as well.”

Sherine Huntley Jones, head of the Vector Control Programme within the Ministry of Health

There have also been a number of suspected deaths from the illness. Thus the Government of Jamaica has decided to pull out the equivalent of a Neutron Bomb.

They've decided to release sterile mosquitoes to halt the reproduction of the female Aedes aegypti mosquitoes that carries and spreads the disease as reported in the article “Gov’t To Release Sterile Mosquitoes To Combat Dengue”, Published Wednesday February 20, 2019, The Jamaica Gleaner.

The statistics so far looks grim. As of February 8, there were have been:

1.      1,166 suspected, presumed or confirmed dengue cases since the start of the year

2.      1,023 suspected, presumed or confirmed dengue cases in 2018

So come 2020, the Government of Jamaica will release 500,000 sterile male mosquitoes into the environment per week. The idea is that will mate with the female Aedes aegypti mosquitoes responsible for spreading the deadly dengue virus and produce stillborn eggs that never hatch.

So how is this being done?

How male Aedes aegypti mosquitoes are sterilized

Sterilize Aedes aegypti mosquitoes is basically making it so that their reproductive organs cannot fertilize the female mosquitoes.

According to Sherine Huntley Jones, head of the Vector Control Programme within the Ministry of Health, there are three (3) ways to sterlize the mosquitoes:

1.      Gene manipulation

2.      Irradiation

3.      Wolbachia Bacteria

Jamaica has chosen the Irradiation, as it is more suited to quick mass production of 500,000 sterile male mosquitoes per week. “Jamaica is using the radiation methodology. At the National Public Health Laboratory in Kingston, we are into mass production of mosquitoes. We are now standardising our procedure for mass growing, with the intention of rearing enough males so we can sterilize and release them,” said Sherine Huntley Jones, head of the Vector Control Programme within the Ministry of Health.

This makes it more like a factory production line where batches of them can be made and quality control procedures can be performed to makes sure they are all sterile, as pointed out by Sherine Huntley Jones, quote: “Jamaica is using the radiation methodology. At the National Public Health Laboratory in Kingston, we are into mass production of mosquitoes. We are now standardising our procedure for mass growing, with the intention of rearing enough males so we can sterilize and release them.”

With a million already being processed for sterilization, Health Minister Dr Christopher Tufton is counting on them to do a better job than fogging. Clearly they cannot keep using the same approach, as it is not working, as pointed out by Minister Tufton, quote: “We cannot engage the same approach to tackling and controlling the mosquito population, like fogging and applying chemical to water. We visited Cayman and looked at their mosquito-control centre. They told us the mosquitoes used to literally bite cattle till death. Mosquitoes are not so much of a nuisance [there] anymore”.

So are there any potential hazards to the environment?

 Sterile Mosquitoes and Reproduction - Females can potentially mutate

Sherine Huntley Jones was speaking with The Gleaner at the Spanish Court Hotel, Valencia, during a seminar titled ‘Mosquito-Borne Diseases: Dengue Fever Impact on the Workforce and Communities’.

The event, put on by the Manpower and Maintenance Services Limited and held in collaboration with the Caribbean Health Management Consultants Ltd and H&L Agro, was fairly well attended.

Good to note here that it is the females that bite and transmute; males merely fertilize the females, hence the reason why they are being targeted. “Males do not transmit disease. Males do not bite. When you hear we are releasing mosquitoes, do not panic! The females are the ones that bite. They need the blood to develop eggs. So we will release the males with view of them mating with wild females to reduce the population,” Jones pointed out.

Albeit there is no danger as it related to irradiated mosquitoes as pointed out in the article Scientist Says Nothing To Fear From Release Of Sterile Mosquitoes, Published Wednesday February 20, 2019, The Jamaica Gleaner. 

But here is the problem.

Mosquitoes and Parthenogenesis – Mutations possible to adapt to decline in males

The female Aedes aegypti mosquitoes is not the only mosquito in town; a new breed is already in the island as pointed out by Minister Tufton, quote: “So what we do is go out, collect samples, breed them, and dissect them. Through the unit, we have discovered that there is a new species of mosquito in Jamaica, which we never knew of before. So we have to apply different methods to control it”.

Albeit different breeds of mosquitoes cannot interbreed, it might be able to interbreed with the sterile males and reproduce. This is because for some insects, they can reproduce asexually, needing only the stimulation of sexual contact to reproduce i.e. male courtship stimulates them.

This method of reproduction is called parthogenesis and is common among Greenflies, stick insects, aphids, water fleas, scorpions, termites and honey bees (Folden, 2018). Albeit it has not been seen in mosquitoes, scientists are yet explain how other insect and animals evolved to develope this trait.

The examples listed are all capable of reproducing without males, using parthenogenesis. In the case of the honey bee, the use of parthenogenesis has evolutionary benefits, as they elect to use parthenogenesis when the local population requires more workers, or more queens.

The possibility exists that millions of years ago, during their evolution, the female gender of these insects and animals that are capable of parthenogenesis developed this trait due to a response in a drop in their male sex partners. Albeit mosquitoes have never faced this problem as honeybees doe, being as they are not communal creatures, they can potentially evolve this capability due to deliberate generic mutation if their reproductive system senses a threat to their continued existence.

Thus, albeit unlikely, the mosquitoes over time, may evolve a mechanism to basically switch from sexual to asexual reproduction and thus thwart irradiation and other threats to their existence.

Being as they reproduce so fast and the Aedes aegypti have a live cycle of 1.5 to 3 and produce on average 100 to 200 eggs per batch (Dengue virus Net, 2019), this evolutionary adjustment may occur rapidly, allowing them to adapt possible in less than 1000 or iterations or life cycles.

Thus by 2025, they may be back at it again, this time reproducing via parthenogenesis, having recovered from the initial shock of their numbers being depleted by irradiation. Such insects, once they interact with each other, can be induced to fertilize their eggs without male gamete.

If the females adapted to irradiation in this way, by 2025 they could continue to reproduce irregardless, producing females that can self-fertilize via parthenogenesis and pass on this trait to their young.

References:

1.      Dengue virus Net. (2019). Retrieved from http://www.denguevirusnet.com/life-cycle-of-aedes-aegypti.html 

2.      Folden, S. (2018). ANIMALS THAT DON'T HAVE A MALE FOR REPRODUCTION. Retrieved from https://animals.mom.me/animals-dont-male-reproduction-9838.html