The mosquito microbiome: An ally in the fight against disease

The annoying buzz of pesky little mosquitoes. At this time of year, the sound can be heard in backyards all around the world. Due to emerging threats like Zika and Dengue virus, people are becoming more and more familiar with the harm these little devils can cause. While vaccines and treatments for many mosquito-borne illnesses remain elusive, some researchers are placing new hope in other micro-organisms who may be able to play a role in preventing these dangerous diseases.

Previous work focused on malaria and its vector, the anopheline mosquitoes, has implicated micro-organisms, such as bacteria or fungi, within the mosquito to have an effect on the mosquito's ability to transmit the disease. Numerous studies in both Anopheles stephensi and Anopheles gambiae have shown that microbes in their midguts can influence the malarial parasite's ability to develop and transmit to new hosts. This is also not a new concept in the Aedes mosquitoes, the vectors for many of the mosquito-borne viruses. Wolbachia bacteria have been successfully introduced multiple times into these mosquitoes to prevent infection in the past.

Most previous studies have focused on introducing microbes to adult mosquitoes. In the field, this naturally presents challenges with application as adult mosquitoes are constantly migrating from place to place. However, recent work highlights that similar strategies could be used on mosquito larvae to influence their ability to transmit disease as adults. Larvae are much more targetable, due to the relative ease of identifying larval development sites.

In the latest study of the mosquito microbiota and its effects on vectorial capacity (the ability of a vector, like the mosquito, to transmit a particular disease), researchers found that differences in bacterial colonization of larvae could have an effect on the adult mosquito's traits. This means that by changing the bacteria larvae are exposed to, you could influence their ability to transmit disease as adults.

While there are many environmental concerns that will need to be addressed before a strategy altering the bacterial make-up of mosquito breeding sites, this new study and the growing body of work focusing on the mosquito microbiome's effects on vectorial capacity offer hope for new strategies to control disease spread. Perhaps some day we will be able to add a simple pellet of bacteria to a pool of water with mosquito larvae and prevent all the subsequent adults from transmitting disease. This may seem like a far-fetched dream today, but with continued research, it could one day be a reality.

Zika virus--an emerging infectious disease or an old nuisance?

Zika virus has been peppering the news the last few weeks as cases have begun to emerge in the United States. What the news anchors most likely won’t tell you is that Zika is just the most recent of the “tropical” diseases to make its way into the US. Also, they probably won’t mention that transmission of Zika within the US is unlikely at this point, so efforts for disease control and eradication should be focused at the epicenter of the outbreak, South America. Here are the facts of this disease.

Zika is not a new virus. Outbreaks have occurred throughout Africa, Southeast Asia, and the Pacific Islands since the 1950's, long before the outbreak of 2015 that caught the media buzz. The infections spread to Brazil in May 2015, and have disseminated from there for the past 9 months. Zika virus is transmitted between people by the bite of an infected female Aedes mosquito. The Aedes mosquito is also responsible for the transmission of Dengue virus and the emerging Chicunguña virus, which have also recently popped up on the radar of Americans. These mosquitoes are very common near the equatorial zone of the globe, including the southern US states, but not as common farther north.

They are known to lay eggs in bodies of standing water, which can be as small as a bucket. Once they reach adulthood, a female must take a bloodmeal in order to lay her eggs. This genus of mosquito prefers to feed on humans above other mammals, and they tend to feed during the daytime. Each bloodmeal is an opportunity to pick up or spread the virus.

At this time, the only real way to deal with Zika virus infection is to prevent mosquito bites. There is no vaccine for the virus, and also no cure. Once infected, an individual has about a one in five chance of developing illness. However, it is important to remember that even those who do not develop clinical symptoms can contribute to spread of the disease as the virus replicates in their cells. The most common clinical symptoms include fever, rash, joint pain, and conjunctivitis. In most cases, the disease is mild and resolves itself in a few days. The real danger that has been identified with Zika virus is the risk that it poses to pregnant women. Zika has been linked to microcephaly in the developing fetus, leading to birth defects and lifelong challenges.

Now for my own opinions. Since the same mosquitoes can carry the Zika virus as carry the Dengue and Chicunguña viruses, fighting all three together through mosquito control is a logical step. In the United States, we are fortunate to have the luxury of air conditioned buildings with firm walls and screened windows, keeping us at a lower risk of exposure to mosquito bites. This is not the case in many other countries. If we, in America, want to stop the threat of Zika (and other mosquito-bourne pathogens), we should think about focusing our efforts on expanding mosquito control methods in other countries. Of course, it would be great to develop a vaccine for this disease; but vaccine development takes many years, and that strategy would require a separate vaccine for each of the mosquito-bourne diseases. Vaccination is a great long-term goal, but to have the most impact in the short-term, vector control is an essential component of the strategy. 

The fight against infectious diseases is difficult and often disheartening. As soon as one outbreak is under control, another arises. As a global community, we just wrapped up the Ebola crisis, and now another potential crisis is emerging right in front of use. But it is important to remember our past successes as a global community that works together to save the lives of everyone at risk from these infections. As has been done with smallpox and almost done with polio, diseases can be controlled and even eradicated if we can just work together and find the right way to address them.