Wolbachia and the Prevention of Mosquito-Borne Diseases

Aedes aegypti is a mosquito that transmits both dengue and Zika virus disease.
Aedes aegypti is a mosquito that transmits both dengue and Zika virus disease. | Source

A Potentially Useful Parasite

Wolbachia is a common insect parasite that appears to be harmless to humans. The bacterium may not kill its host, but it does affect the insect's biology. Researchers have discovered that Wolbachia inhibits the replication of viruses in mosquitoes. This ability could be very useful, since mosquitoes transmit some unpleasant and sometimes dangerous viral diseases. Deliberately infecting the mosquito population with the bacterium may prevent several illnesses in humans, including dengue and Zika virus disease.

Some people may wonder why scientists are infecting mosquitoes with bacteria instead of killing the insects outright. One reason is that once enough female mosquitoes are infected, the infection process is self-sustaining because the females pass bacteria to their offspring. Another reason is that mosquitoes are becoming resistant to the present insecticides. In addition, some insecticides are harmful for the environment. This is why research into mosquito control methods and vaccines for humans is so important.

Wolbachia bacteria (inside the circles with white borders) in an insect cell
Wolbachia bacteria (inside the circles with white borders) in an insect cell | Source

Wolbachia was discovered in 1924 by S. Burt Wolbach and Marshall Hertig. They found the bacterium in Culex pipiens, a widespread insect generally known as the common house mosquito.

The Wolbachia Bacterium

Insects belong to the phylum Arthropoda. Wolbachia is found in many insects, other arthropods, and some members of the phylum Nematoda (roundworms). It occurs naturally in some mosquitoes and has been added successfully to others.

Wolbachia is said to be a heritable microorganism because it passes from one generation to the next. It lives inside its host's cells, including those of the ovaries and testes. Some bacteria enter the egg cells. During fertilization, a sperm inserts its nucleus into an egg. As the fertlized egg multipliies to make an insect, the bacteria in the egg reproduce and become part of the new individual.

Wolbachia affects its host's reproductive biology in intriguing ways that are not well understood. The bacterium favours the production of female offspring and hinders the production of males. Since Wolbachia is passed from one generation to the next in eggs, increasing the percentage of females in the population is beneficial for the bacterium.

Exploring Wolbachia Bacteria in Mosquitoes

How Does Wolbachia Favour the Production of Females?

Researchers have found that the bacterium can control the gender of host offspring in the following ways, although it may not produce each effect in every type of host.

  • Male killing: males die during the larval stage of their development
  • Feminization: larval males develop into females or infertile males
  • Parthenogenesis: reproduction occurs without the presence of males, making all the offspring females

Cytoplasmic Incompatibility in Infected Mosquitoes

Wolbachia has another interesting effect on its host's reproduction. The effect is known as cytoplasmic incompatibility and has been observed in at least some of the mosquitoes that cause disease. As a result of the bacterium's presence, under certain conditions the eggs and sperm are no longer compatible and can no longer produce viable offspring.

Cytoplasmic incompatibility operates when the following conditions exist, as shown in the diagram below.

  • An infected male mates with an uninfected female.
  • An infected male mates with a female infected by a different strain of Wolbachia.

An infected female is able to reproduce when she mates with an uninfected male or with a male infected by the same strain of Wolbachia. The net effect of cytoplasmic incompatibility is the spreading of the female's strain of Wolbachia to the next generation.

Cytoplasmic Incompatibility Induced by Wolbachia

The circle with a cross hanging below it is the biological symbol for a female. The circle with an arrow on its right is the symbol for a male.
The circle with a cross hanging below it is the biological symbol for a female. The circle with an arrow on its right is the symbol for a male. | Source

The species of Wolbachia used in mosquito experiments is Wolbachia pipientis. The species exists in slightly different forms known as strains. Different strains have different effects on mosquitoes.

Mosquitoes That Transmit Dengue and Zika Virus Disease

The insect with the scientific name Aedes aegypti has the common name yellow fever mosquito. As this name suggests, the insect can transmit the disease known as yellow fever to humans. It can also transmit chikungunya, dengue (pronounced dengee) and Zika virus disease. It's the main vector or transmitter for these diseases. It's native to Africa but has spread to tropical and semitropical areas of the United States.

Aedes albopictus also transmits viruses to humans, including the dengue and Zika viruses, but to a lesser extent than its relative. It's native to Southeast Asia but has spread to the United States. Its range has extended further north than that of its relative because it can tolerate a cooler environment.

Aedes albopictus or the Asian tiger mosquito
Aedes albopictus or the Asian tiger mosquito | Source

Mosquito Bites and Disease

Only female mosquitoes bite humans and suck up blood. They need some of the nutrients in blood in order to produce their eggs. The females inject saliva containing an anticoagulant into the wounds that they create. The anticoagulant stops coagulation or blood clotting, enabling a mosquito to get a good drink. The injected saliva may contain viruses that can cause disease. These viruses enter the saliva from the insect's salivary glands and travel into the victim's bloodstream with the anticoagulant.

When a mosquito withdraws blood from an infected person, it may withdraw viruses as well. If these viruses get into the salivary glands, they may pass into the bloodstream of an uninfected person during a mosquito bite.

The Three Phases of Dengue Fever


Hypotension is low blood pressure. Pleural effusion is the collection of fluid around the lungs. Ascites is the collection of fluid between the lining of the abdominal cavity and the organs in the cavity.

Dengue Fever

Dengue or dengue fever is a tropical, flu-like illness that is often mild but is sometimes serious. It's caused by the dengue virus. Possible symptoms are shown in the illustration above. A patient may not experience all of the symptoms when they have the disease. The disorder is also known as breakbone fever because of the pain that it sometimes causes.

Dengue fever is classified as uncomplicated or severe. A "complication" of a disease is a secondary effect or disease that develops after the main illness. Patients generally recover from uncomplicated dengue. Severe dengue often requires hospital treatment and may even be deadly, however.

In some parts of the world, dengue is a major and widespread public health issue. Both dengue and Zika virus disease (sometimes called Zika fever) generally occur in warm climates outside of North America. Recently outbreaks of each disease have occurred in the United States, however - dengue in Hawaii and Zika virus disease in Florida.

Information about the Zika Virus

Zika Virus Disease

The Zika virus is named after the Zika Forest in Uganda, where it was discovered in 1947. (This is why its name always begins with a capital letter.) It's transmitted mainly by a bite from a mosquito in the genus Aedes, especially Aedes aegypti. More rarely, it's transmitted by sexual contact. The infection often causes mild symptoms or even none at all. The complications may be far from mild, however.

Symptoms that may develop from a Zika virus infection include a fever, a rash, joint pain and conjunctivitis (inflammation of the conjunctiva, or the membrane covering the surface of the eye and the inside of the eyelid). The affected person may also experience a headache and muscle pain.

Zika infection during pregnancy can cause a serious birth defect called microcephaly and other severe fetal brain defects. Guillain-Barre syndrome (GBS), an uncommon sickness of the nervous system, is also very likely triggered by Zika in a small number of cases.

— CDC (Centers for Disease Control and Prevention)

Complications of Zika-Virus Disease

As can be seen from the quotes shown above and below, scientists say that Zika virus disease can cause microcephaly. This is a condition in which a baby is born with an unusually small head. The condition is often (but not always) accompanied by incomplete brain development and lifelong problems for the child. Zika virus infection of the mother during pregnancy is one cause of microcephaly. The virus is thought to cross the placenta and reach the developing baby, although how it does this is still unknown.

The Zika virus very likely causes Guillain-Barré syndrome as well as microcephaly. As can be seen in the different wording of the WHO and CDC quotes, however, some scientists consider this association to be less obvious than the link between the virus and microcephaly.

After a comprehensive review of evidence, there is scientific consensus that Zika virus is a cause of microcephaly and Guillain-Barré syndrome.

— WHO (World Health Organization)

Guillain-Barré Syndrome

Guillain-Barré syndrome is an uncommon disorder in which a person's immune system attacks part of their nervous system. Symptoms of the disorder include weakness, tingling, and in severe cases, paralysis. The latter situation is a medical emergency because the paralysis may involve the breathing muscles and the muscle in the heart. The syndrome can be treated, however, and most people recover. Some are left with residual symptoms such as weakness. In many cases, the syndrome appears after the person has experienced a viral infection.

How a Virus Replicates

A virion is an individual virus. Its genetic material is either RNA or DNA. Both the dengue and the Zika virus contain RNA.
A virion is an individual virus. Its genetic material is either RNA or DNA. Both the dengue and the Zika virus contain RNA. | Source

The Zika virus and the dengue virus are related to one another. They belong to a group known as flaviviruses.

Viral Replication

Wolbachia enables at least some mosquitoes to avoid infection by specific viruses. It works by stopping the viruses from replicating inside a mosquito's cells. During an infection of an insect cell (or of our cells), a virus particle enters the cell and "forces" it to make new virus particles. These leave the cell and invade new ones, repeating the replication process. A large viral population is often produced.

The discovery that Wolbachia can somehow stop the replication of certain disease-causing viruses is an exciting one. Without virus particles in its salivary gland, a mosquito will be unable to spread viral diseases when it bites humans.

Controlling Dengue with Wolbachia

Effects of Wolbachia on Mosquitoes and Dengue

Wolbachia doesn't occur naturally in Aedes aegypti. Wolbachia insertion is already being used experimentally in an attempt to fight dengue, however. Researchers have learned how to insert the bacteria into mosquito eggs without killing the eggs.

The Eliminate Dengue Program is an international effort led by Monash University in Australia. The main goal of the program is not to reduce the number of mosquitoes but to prevent them from carrying the dengue virus. The scientists in the program rear mosquitoes with added bacteria and then release the adults into the environment, where they mate with wild mosquitoes. The inserted bacteria stay alive in their hosts and gradually spread through the population via the eggs of infected females. They also appear to reduce the incidence of dengue in the area. Quantitative data is needed to demonstrate the correlation between altered mosquitoes and dengue reduction, however.

Increasing the percentage of bacteria in a mosquito population takes time, but it should be a safe and self-sustaining process. The researchers are monitoring the results of their experiments carefully. So far, there is no evidence that the mosquitoes with added bacteria are harmful for humans or the environment.

Some researchers are using a different tactic to control mosquitoes. They are creating bacterially-altered mosquitoes in order to decrease the insect population by cytoplasmic incompatibility.

Zika virus (artificially coloured red)
Zika virus (artificially coloured red) | Source

Wolbachia and Zika Virus Disease

Given the preliminary success of Wolbachia in the fight against dengue, some researchers suspect that the same results will be obtained with the Zika virus. Encouraging results have been obtained with mosquitoes in the lab. Researchers have shown that infection by a specific strain of Wolbachia decreases the amount of Zika virus in mosquitoes and eliminates the virus from their salivary glands. It has not yet been demonstrated that these altered mosquitoes lack the ability to transmit Zika virus disease to humans, but the possibility is tantalizing.

The use of Wolbachia is being investigated in relation to other mosquito-borne diseases, including malaria. It would be wonderful to have an effective and environmentally safe method to control diseases transmitted by mosquitoes. They are annoying and troubling insects.

© 2016 Linda Crampton

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Comments 28 comments

Jackie Lynnley profile image

Jackie Lynnley 2 months ago from The Beautiful South

Wow, what information and so very interesting. I had heard some about what they are trying to do with the Zika and how it is unlikely it will spread easily. I sure hope something is done, I am a mosquito magnet and I get bit every day no matter how careful I try to be. Would be nice if I was building up an immunity but I know that is not how it works!

Thanks for a much needed article! Shared.

AliciaC profile image

AliciaC 2 months ago from British Columbia, Canada Author

Thanks for the comment and the share, Jackie! Mosquitoes are certainly a nuisance. I hope the Zika virus doesn't spread further into North America.

Mel Carriere profile image

Mel Carriere 2 months ago from San Diego California

Although this Wolbachia certainly sounds like a boon in the battle of mosquito-borne diseases, I always wonder if there might not be consequences that we have not been able to identify. Throughout the American West they brought in Salt Cedars (Tamarisk) for erosion control. Now the Salt Cedars have supplanted the native vegetation, and are near impossible to eradicate. Sometimes the cure winds up to be worse than the disease. Perhaps we should research this more extensively before unleashing another Pandora's box into the wild.

Wonderfully written hub and, as always, very educational.

AliciaC profile image

AliciaC 2 months ago from British Columbia, Canada Author

Hi, Mel. Thank you very much for the comment. I think that your concern is very valid. Every time we try to take control of nature there are risks. As you say, Wolbachia sounds like a boon. It could be very helpful in preventing disease, but it's important that we're careful and learn as much as we can about the bacterium.

billybuc profile image

billybuc 2 months ago from Olympia, WA

With Bev's recent illness, I find myself hopelessly behind in my readings, so I'm sorry I'm so late for this one. Having said that, thank you for your continued dedication to learning and quality writing.

AliciaC profile image

AliciaC 2 months ago from British Columbia, Canada Author

You're not late at all, Bill! I only published the article yesterday. Thank you very much for commenting. I'm so glad that Bev is better. I hope the upcoming week goes much better for both of you.

BlossomSB profile image

BlossomSB 2 months ago from Victoria, Australia

What an interesting article. I also enjoyed seeing the images of the mosquito. In PNG the one that carries filaria has stripes on its body. I, too, am wondering if this particular bacterium can be harmful to other insects that may be useful to humanity.

AliciaC profile image

AliciaC 2 months ago from British Columbia, Canada Author

Hi, Blossom. Thanks for the comment and for sharing the information. I very much hope that the bacterium isn't harmful but is a solution instead. We certainly need help in fighting mosquito-borne diseases.

FlourishAnyway profile image

FlourishAnyway 2 months ago from USA

While it's certainly good news for people, I do wonder if they've fully investigated the downstream environmental impact as much as they think they have, particularly considering unintended consequences. Nature is such a delicate balance, and many migratory birds, song birds, waterfowl and some fish depend on mosquitoes. You've done an excellent job present this information. Zika, dengue and other mosquito-bourne illnesses are frightening because they can literally happen to anyone.

Larry Rankin profile image

Larry Rankin 2 months ago from Oklahoma

Always informative and interesting. Another wonderful article.

AliciaC profile image

AliciaC 2 months ago from British Columbia, Canada Author

Hi, Flourish. Yes, I think "as much as they think they have" is a key phrase. While I hope the research into fighting disease with Wolbachia continues, I think that it's important that researchers monitor the effects on the environment as widely and as carefully as possible. Thanks for the thoughtful comment.

AliciaC profile image

AliciaC 2 months ago from British Columbia, Canada Author

Thank you very much for the kind comment, Larry.

teaches12345 2 months ago

I find the topic quite interesting as we look into the Zika virus. Here in South Florida, we are taking precautions to prevent the spread. Thank you for the quality writing and education on the topic of Wolbachia.

AliciaC profile image

AliciaC 2 months ago from British Columbia, Canada Author

Thank you very much for the comment and for sharing the information about what is happening in Florida, Dianna. I hope the situation doesn't become worse than it already is.

MsDora profile image

MsDora 2 months ago from The Caribbean

"Mosquitoes are becoming resistant to the present insecticides." Now, that's scary. Mosquito bites are almost a daily occurrence so imagine the fear that exists. Thanks for the important research and the quality presentation.

AliciaC profile image

AliciaC 2 months ago from British Columbia, Canada Author

Hi, MsDora. Thanks for the visit. The mosquito situation is frustrating. Some researchers say that we need to use a combination of methods to control them. I hope we are soon able to prevent the diseases that they transmit.

Buildreps 2 months ago

Very interesting article, Alicia. I enjoyed reading it! Very well explained how the manipulation of mosquitoes population by the Wolbachia works. It offered me profound insights in this issue. Thanks for that!

AliciaC profile image

AliciaC 2 months ago from British Columbia, Canada Author

Thanks, Buildreps. I appreciate your comment very much, as I always do!

DDE 2 months ago

An interesting and a topic not be ignored. You shared a useful hub.

AliciaC profile image

AliciaC 2 months ago from British Columbia, Canada Author

Thank you for the visit and the comment, Devika.

Deb Hirt 8 weeks ago

This is an interesting article. A sci-fi story was written decades ago about females impregnating themselves without the need for a male, which immediately came to mind while reading this. Oddly enough, mosquitos only use, in my opinion, is the fact that they do pollinate.

AliciaC profile image

AliciaC 8 weeks ago from British Columbia, Canada Author

Hi, Deb. The story that you've described sounds interesting! Thank for commenting and for sharing the information.

Yeeshouw W. 5 weeks ago

This is a very well written article. This gave tons of information that I could use for my solution to stop mosquito-borne diseases harming humans without harming them in the prospect. Could you please send me your e-mail for further questions I have?

Thank you,


AliciaC profile image

AliciaC 5 weeks ago from British Columbia, Canada Author

Thank you very much for the comment, Yeeshouw W. I appreciate your visit. I'm sorry, but I don't share my email address on my articles. If you have a question, I'll try to help you if you leave another comment.

Yeeshouw W. 5 weeks ago

Thank you Linda,

So I am from a local FLL (FIRST Lego League) team. FLL is a worldwide organization involving all the fields of STEM for all kids from ages 9-14. My name is Yeeshouw and I am from the team Tech-Narwhals. I am in 9th grade. Each year there is a different theme that our research project and robot game revolves around. This year’s theme is Animal Allies. The research prompt is to find an important human-animal interaction and find a way to improve this interaction. As a team, we have recently decided to focus our topic on mosquitoes. We were hoping you could help us broaden research this year. I would be very grateful if you could answer the following questions to the best of your ability.

-Are there any possible solutions to stop mosquitoes getting too close to human populated areas like a certain hormone?

-How is the bacteria, Wolbachia, injected into the mosquitoes like, Ae. aegypti?

-How do you think that we could improve one this Wolbachia solution?

-What is the reliability one the Wolbachia solution?

-Finally, what is the most harmful mosquito-borne disease in your opinion?

Thank you very much for your time and consideration. We really appreciate your expertise and professional opinion. If there are some question you are unable to answer could you please guide me to another source that could help me with my research? May I comment later if any question in mind pop up?

Best regards,


AliciaC profile image

AliciaC 5 weeks ago from British Columbia, Canada Author

Hi, Yeeshouw. The FIRST Lego League sounds very interesting! Since I'm a science teacher and writer but not an entomologist, I think it would be a good idea to tell you about some websites run by scientists that should be able to help you. The eliminate dengue website is run by people injecting mosquitoes with Wolbachia. They have a "Contact" section where you can ask the researchers questions. The WHO (World Health Organization) and the CDC (Centers for Disease Control and Prevention) websites have information about the number of people infected by different mosquito-borne diseases.

Good luck with your project. Feel free to comment later. I should be able to suggest places where you can get information.

Yeeshouw W. 5 weeks ago

Hi, Linda. Thank you so much for these sources to help me out with my research. I really appreciate your help. I'll be sure to look at these websites as they sound very interesting.

Thank you again for these sources,


AliciaC profile image

AliciaC 5 weeks ago from British Columbia, Canada Author

You're welcome, Yeeshouw.

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    Linda Crampton (AliciaC)1,244 Followers
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    Linda Crampton is a teacher with an honours degree in biology. She enjoys writing about human biology and the science of health and disease.

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