Nav: Home

Mosquito 'spit glands' hold key to curbing malaria, study shows

August 12, 2019

Mosquitoes can harbor thousands of malaria-causing parasites in their bodies, yet while slurping blood from a victim, they transmit just a tiny fraction of them. In an effort to define precisely the location of the parasite bottleneck, Johns Hopkins Medicine scientists say they have discovered that the parasites are stopped by a roadblock along the escape route in the insect's spit glands, a barrier that could potentially serve as a novel target for preventing or reducing malarial infection.

"Our findings add substantial detail to the role of mosquito salivary glands as the gateway organs for diseases spread by these insects," says Deborah Andrew, M.S., Ph.D., professor of cell biology at the Johns Hopkins University School of Medicine. "By enhancing transmission barriers that naturally exist in mosquitos, we potentially can block the spread of malaria and other deadly mosquito-borne diseases, like Zika fever."

An estimated 220 million people worldwide, mostly in tropical and subtropical regions, have malaria, and more than 400,000 die of the parasite infection each year, according to the World Health Organization. Marked by disabling fever, chills, fatigue and sweating, the disease can be treated with drugs and prevented with mosquito eradication programs, but the high costs of drugs and eradication methods consistently hamper efforts to reduce malaria's prevalence. Other mosquito-borne diseases, including dengue fever, strike scores of millions more.

A description of the research is published in the Aug. 6 issue of the journal mBio.

Malaria parasites are dependent on female Anopheles mosquitoes to spread in a complex life cycle that begins when mosquitos eat male and female parasite sex cells during a blood meal from an infected animal host. The cells wind up in the mosquito's gut, where they fuse to form fertilized eggs that then squeeze through the gut's lining and become encased in cysts in the insect's body cavity. In these cysts, the parasites begin a reproductive frenzy, making more and more copies of themselves. When the cysts finally burst, the parasites raid the salivary gland by the hordes, ready to be squirted out when the mosquito takes its next blood meal. But scientists have long observed that most of them never make it out of the mosquito.

"Even though thousands of parasites invade the salivary gland, less than a 10th of them are transmitted during a mosquito bite," says Michael Wells, Ph.D., postdoctoral researcher in Andrew's laboratory and the study's lead author. "So, we knew that the salivary gland is blocking the parasites from getting out, but we didn't know exactly how."

The Anopheles mosquito's salivary gland is made up of three lobes of saliva-producing cells. The lobes are encased in a protective sheet called the basement membrane, and in each lobe are long ducts that extend into the insect's mouth. For release, the parasites must first go through the basement membrane, penetrate a layer of salivary cells and then swim across a space called the secretory cavity to reach the salivary duct.

To study how the salivary gland might obstruct malaria transmission, the researchers first let Anopheles mosquitoes feed on rodent blood enriched with malaria parasites. Since the mosquitoes decided how much they ate, each one consumed a different quantity of parasites. This offered the researchers data for different quantities of parasitic infection from hundreds of mosquito salivary glands.

The researchers then systematically mapped out the parasites' location by dissecting salivary glands from these mosquitos and looking for the parasites under high-powered microscopes. They found that most parasites were either inside the basement membrane or in the secretory cavity. But only a few parasites were in the salivary ducts.

"The parasites seem to have no trouble getting into the salivary glands," says Wells. "So, this told us that the obstruction happens later, when parasites are trying to get to the salivary duct."

Next, the researchers zoomed in on the cell layers in each lobe of the salivary gland. They found that most parasites appeared unable to leave the secretory cavity and were congregating at a fibrous, sturdy wall made of a substance called chitin that forms around the salivary ducts.

Some parasites, however, were able to tunnel through the chitin wall and reach the salivary duct, but like traffic bottlenecks, the narrow opening they burrowed into allowed only a few parasites to pass through. Wells says the lucky parasites that make it through the tough duct wall are likely the ones that are released during a bite.

If the chitin wall around salivary ducts can be fortified, infections may be thwarted. "Our study is a first step in better understanding how salivary glands in malaria-carrying mosquitoes limit the transmission of disease parasites," says Andrew. "In the future, we hope this information will advance strategies to limit transmission and uncover how other insects have evolved ways to affect disease transmission."
-end-
The research was supported by the National Institutes of Health (NIH RO1DE013899), a Johns Hopkins Malaria Research Institute postdoctoral fellowship and Bloomberg Philanthropies.

DOI: doi.org/10.1128/mBio.01238-19

News release written by science writing intern Vandana Suresh for the Johns Hopkins Institute for Basic Biomedical Sciences.

Johns Hopkins Medicine

Related Science Articles:

75 science societies urge the education department to base Title IX sexual harassment regulations on evidence and science
The American Educational Research Association (AERA) and the American Association for the Advancement of Science (AAAS) today led 75 scientific societies in submitting comments on the US Department of Education's proposed changes to Title IX regulations.
Science/Science Careers' survey ranks top biotech, biopharma, and pharma employers
The Science and Science Careers' 2018 annual Top Employers Survey polled employees in the biotechnology, biopharmaceutical, pharmaceutical, and related industries to determine the 20 best employers in these industries as well as their driving characteristics.
Science in the palm of your hand: How citizen science transforms passive learners
Citizen science projects can engage even children who previously were not interested in science.
Applied science may yield more translational research publications than basic science
While translational research can happen at any stage of the research process, a recent investigation of behavioral and social science research awards granted by the NIH between 2008 and 2014 revealed that applied science yielded a higher volume of translational research publications than basic science, according to a study published May 9, 2018 in the open-access journal PLOS ONE by Xueying Han from the Science and Technology Policy Institute, USA, and colleagues.
Prominent academics, including Salk's Thomas Albright, call for more science in forensic science
Six scientists who recently served on the National Commission on Forensic Science are calling on the scientific community at large to advocate for increased research and financial support of forensic science as well as the introduction of empirical testing requirements to ensure the validity of outcomes.
World Science Forum 2017 Jordan issues Science for Peace Declaration
On behalf of the coordinating organizations responsible for delivering the World Science Forum Jordan, the concluding Science for Peace Declaration issued at the Dead Sea represents a global call for action to science and society to build a future that promises greater equality, security and opportunity for all, and in which science plays an increasingly prominent role as an enabler of fair and sustainable development.
PETA science group promotes animal-free science at society of toxicology conference
The PETA International Science Consortium Ltd. is presenting two posters on animal-free methods for testing inhalation toxicity at the 56th annual Society of Toxicology (SOT) meeting March 12 to 16, 2017, in Baltimore, Maryland.
Citizen Science in the Digital Age: Rhetoric, Science and Public Engagement
James Wynn's timely investigation highlights scientific studies grounded in publicly gathered data and probes the rhetoric these studies employ.
Science/Science Careers' survey ranks top biotech, pharma, and biopharma employers
The Science and Science Careers' 2016 annual Top Employers Survey polled employees in the biotechnology, biopharmaceutical, pharmaceutical, and related industries to determine the 20 best employers in these industries as well as their driving characteristics.
Three natural science professors win TJ Park Science Fellowship
Professor Jung-Min Kee (Department of Chemistry, UNIST), Professor Kyudong Choi (Department of Mathematical Sciences, UNIST), and Professor Kwanpyo Kim (Department of Physics, UNIST) are the recipients of the Cheong-Am (TJ Park) Science Fellowship of the year 2016.
More Science News and Science Current Events

Trending Science News

Current Coronavirus (COVID-19) News

Top Science Podcasts

We have hand picked the top science podcasts of 2020.
Now Playing: TED Radio Hour

Making Amends
What makes a true apology? What does it mean to make amends for past mistakes? This hour, TED speakers explore how repairing the wrongs of the past is the first step toward healing for the future. Guests include historian and preservationist Brent Leggs, law professor Martha Minow, librarian Dawn Wacek, and playwright V (formerly Eve Ensler).
Now Playing: Science for the People

#565 The Great Wide Indoors
We're all spending a bit more time indoors this summer than we probably figured. But did you ever stop to think about why the places we live and work as designed the way they are? And how they could be designed better? We're talking with Emily Anthes about her new book "The Great Indoors: The Surprising Science of how Buildings Shape our Behavior, Health and Happiness".
Now Playing: Radiolab

The Third. A TED Talk.
Jad gives a TED talk about his life as a journalist and how Radiolab has evolved over the years. Here's how TED described it:How do you end a story? Host of Radiolab Jad Abumrad tells how his search for an answer led him home to the mountains of Tennessee, where he met an unexpected teacher: Dolly Parton.Jad Nicholas Abumrad is a Lebanese-American radio host, composer and producer. He is the founder of the syndicated public radio program Radiolab, which is broadcast on over 600 radio stations nationwide and is downloaded more than 120 million times a year as a podcast. He also created More Perfect, a podcast that tells the stories behind the Supreme Court's most famous decisions. And most recently, Dolly Parton's America, a nine-episode podcast exploring the life and times of the iconic country music star. Abumrad has received three Peabody Awards and was named a MacArthur Fellow in 2011.