Could Mosquito Saliva Prevent Another Pandemic?

 

 

Video Essay Transcript:

One of the most prevalent problems in the world today is the COVID-19 pandemic. As many people know, researchers are hard at work on combating this virus. However, many people don’t know that there may be another pandemic on the rise. According to The Journal of Infectious Diseases, mosquito-borne illnesses cause one million deaths each year. The most effective solution to this problem would be to develop vaccines to combat all these diseases which are caused by pathogens, such as bacteria or viruses. While scientists have been working on developing vaccines, it has proven to be very time-consuming and costly because each disease requires a different vaccine. However, a recent study suggests that there may be a way to protect against these pathogens all in one stop. This is possible through the development of a vaccine that would target mosquito saliva. In this study, scientists at the Laboratory of Malaria and Vector Research conducted a clinical trial that found that the “participants in the adjuvanted vaccine group had significantly higher vaccine-specific total IgG antibody responses than those in the vaccine only or placebo groups” (Manning 2020, p. 2003). This adjuvant vaccine is composed of oils and emulsifying agents that enhance the body’s immune reaction to the injection and slow the pathogen clearance against the body’s immune system. Therefore, the study shows that using a vaccine that familiarizes the body with properties in the mosquito spit could help to protect humans from many mosquito-borne pathogens. These findings are important because “in recent decades, mosquito-borne viruses, such as West Nile, chikungunya, dengue, and Zika have re-emerged and spread widely, in some cases pandemically” (Manning 2018, p. 7). So, in order to avoid another situation like the recent COVID-19 pandemic, a vaccine that could potentially be used for protection against many if not all diseases caused by mosquitos is paramount. 

This recent study was conducted in 2017 by Dr. Jessica Manning and her team at the National Institutes of Health Clinical Center in Bethesda, Maryland. It was funded by the Office of the Director and the Division of Intramural Research at the National Institute of Allergy and Infectious Diseases and by the National Institutes of Health. The study was then published in 2020 in The Lancet. Since the 1940s, researchers have observed that mosquito saliva allows pathogens to enter the body more easily. More specifically, the mosquito inserts its proboscis, a mouth-like structure, into the skin. As it probes for blood, the mosquito ejects a salivary mix of vasodilators, anticoagulants, and other anti-hemostatic components into both the epidermis and the dermis that keep the blood flowing. In addition to these factors, mosquito saliva also contains proteins that trigger both innate and adaptive immune responses. It does this by dampening “the host’s antiviral Th1 immune response” and by preoccupying the body, which allows the pathogens to infect the host (Manning 2018, p. 8-9). Dr. Jessica Manning and her team have responded to this issue by testing a vector-targeted salivary protein-based vaccine on humans for the first time ever. They hypothesized that a vaccine targeting proteins in mosquito saliva instead of individual pathogens would protect humans against multiple mosquito-borne infections in one shot and will be more effective at combatting the diseases themselves. This type of vaccine injects genetic code for the antigen rather than the antigen itself in order to infect host cells and instruct the body to make the antigen. This triggers an immune response that mimics what happens during natural infection (Gavi 2021). And in the future, when coming encountering truly infected mosquito saliva, the body is then able to recognize the proteins in the saliva that trigger the immune response and react to the pathogens in the saliva with the preexisting antigens that the body has just made. 

When conducting their clinical trial, they aimed to determine if a vector-targeted vaccine could be used safely in humans to induce immunogenicity to mosquito salivary proteins. In phase one, participants were randomly selected and enrolled in the National Institutes of Health Clinical Center. The trial was double-blind, meaning that neither the researchers nor the participants knew whether they received the placebo or the vaccine. The participants were randomly assigned into three different groups, using block randomization through a computer-generated randomization sequence. The three treatments were 200 nanomoles of AGS-v vaccine, 200 nanomoles of AGS-v with the adjuvant Montanide ISA fifty-one, and sterile water as the placebo. The AGS-v vaccine consisted of “ a combination of four synthetic salivary peptides… ranging from [thirty-two] to [forty-four] amino acids” (Manning 2020, p. 2000). All participants were given injections of their treatment on day zero and day twenty-one. Then, they were exposed to uninfected Aedes aegypti mosquitos on day forty-two to assess the effectiveness of each vaccine. 

Dr. Manning and her team found that targeting the salivary proteins resulted in antibodies that can better attack the pathogens instead of the innate immune response that typically occurs when encountering mosquito saliva. More specifically, the trial showed that the “AGS-v [vaccine] was well tolerated and [the] adjuvanted AGS-v [vaccine] produced an increase in both saliva vaccine peptide-specific antibodies and IFN-γ release compared with [the] placebo at the primary endpoint of day [forty-two]” (Manning 2020, p. 2005). However, the research behind this vaccine is not done because there are some flaws with this study. For instance, some of the participants dropped out along the way, which lead to a small sample size, making the trial less representative of how the population may react to the vaccine. The participants also self-reported mosquito bites which could lead to response bias and skew the results of the study. There are also limitations on who can ethically be tested in this type of study. Since the risk of serious reactions to the vaccine must be taken into consideration, the vaccine can only be tested on humans that aren’t immunocompromised and are healthy. So, it is hard to know the reactions that people with weaker immune systems will have. With all of this said, the design of this study is good because it can be repeated. The study can also be justified because it could save a lot of people from dying by preemptively confronting the next pandemic since it could protect against many possible diseases. So, unlike the coronavirus, researchers won’t have to scramble to determine what the pathogen is and how to vaccinate against it. The vaccine will also be very important to lower-income countries where mosquito-borne diseases are high and paying for multiple vaccines is unrealistic. 

In terms of the future, researchers should continue to run trials on this vaccine in order to see if the results can be replicated, preferably with larger sample sizes. After conducting these trials to evaluate the effectiveness of the vaccine, it will be necessary to identify which diseases the vaccine protects against in terms of mosquito-borne diseases and determine if the vaccine is safe for immunocompromised people. If all of this is done, a mosquito-borne pandemic is less of a threat to our society. Furthermore, this research could even change how we vaccinate in the future by applying this vaccination method to other groups of diseases. Being able to protect against multiple diseases in one doctor’s visit could allow for vaccines to be more accessible to poorer countries that have less access to them because of costs and the ability to take the time to go to the doctor, which would lower death rates worldwide. Maybe this technology could even be used for corona virus-related pathogens and create a vaccine to combat all of the pathogens in this family, ending the pandemic we are in now and the risk of future pandemics due to other various pathogens in the coronavirus complex.

 

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Feature Image

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