This article was updated June 27, 2022 to include Oxitec’s response.
A mosquito infected with the potentially deadly West Nile virus (WNV) was captured last week in a trap in southwest Visalia, the first identified this year.
Cases of WNV-infected mosquitoes in the Delta Mosquito Vector Control District (DMVCD) – the local agency tasked with keeping the mosquito population in check – are common, and this year’s first case came well into the mosquito season.
“It happens every year,” said Erick Arriaga, DMVCD’s community education and outreach coordinator. “This year, it was a little later than usual.”
WNV can lead to West Nile fever, a disease that can, in rare cases, cause swelling of the brain or swelling of the membranes that surround the brain and the spinal column. No human WNV infections have been reported so far in California, according to the California Department of Public Health (CDPH).
“We haven’t had a (local) human case in a while,” Arriaga said.
After the infected mosquito was identified in southwest Visalia, Arriaga says the DMVCD increased its pest-fighting activity there, including additional spraying targeted at reducing the insect population. The move appears to have worked.
“The numbers of mosquitoes in traps are down,” Arriaga said.
West Nile Poses an Annual Threat
Last year, nine people in Tulare County were infected with WNV, eight of whom developed symptoms of West Nile fever. In Kings County, 10 cases were reported, with eight of the patients becoming symptomatic. One of those patients died.
Fresno County saw 17 cases, including one death, and Kern County had 10 cases, none fatal.
The fever is flu-like, causing aches and pains, vomiting, and diarrhea, according to the Centers for Disease Control (CDC). Only about 20% of those who are infected develop symptoms. Some symptomatic sufferers will develop a rash, and about one in 150 infected individuals will experience severe symptoms caused by damage to the central nervous system.
Most who develop symptoms from a WNV infection will recover completely, however, some experience weakness and fatigue that may last for weeks or months. Those who experience severe, life-threatening symptoms may never completely recover from the damage. At its worst, WNV can cause coma, vision loss, muscle weakness, loss of coordination and muscle paralysis, especially in people with existing medical conditions.
On average, one in 10 who suffer damage to the central nervous system dies, the CDC said. There is no vaccine against WNV, and there are no specific medicines intended to treat it. Severe cases frequently require hospitalization.
Company to Release GMO to Slow Invasive Mosquito
Tulare County and the DMVCD are home to more than one species of mosquito. The insect ID’d as infected with WNV was likely a species of Culex mosquito, which can carry pathogens that cause encephalitis, including malaria, which was once a leading cause of illness and death in Tulare County. Culex mosquitoes became more dangerous to humans in 1999, when WNV first appeared in North America during an outbreak in upstate New York.
The county has been invaded by a new species of mosquito, Aedes aegypti – known commonly as the yellow fever mosquito – which was first documented here in the early 2000s. Aegypti is a smaller cousin to the Culex mosquitoes, and despite its name the aegypti does not spread West Nile. Aegypti does spread a handful of rare diseases, none of which, like yellow fever, are known in California, according to the CDPH.
That doesn’t mean those diseases couldn’t eventually spread here, just like the insects that help spread the pathogens that cause them, says Dr. Mustapha Debboun, manager of the DMVCD. Debboun holds a doctorate in medical and veterinary entomology.
“We don’t have it (yellow fever) yet. That doesn’t mean people won’t travel,” he said. “They can bring it here, and we have the vector here.”
To that end, the district is working with Oxitec, a British company that plans to test the use of genetically modified male aegypti mosquitoes to attempt to reduce the population of the invasive insect.
State Still Mulling Release of Modified Mosquitoes
While the federal Environmental Protection Agency has already OK’d the use of the GM aegypti, the state’s Department of Pesticide Regulation (DPR) has yet to give its approval for Oxitec’s plan to release millions of live mosquitoes in Tulare County. The company also hopes to conduct tests in three other California counties – Fresno, Stanislaus and San Bernardino.
According to Oxitec, “the total number of non-biting Oxitec male mosquitoes released during our pilot project in the Florida Keys last year was fewer than 5 million.”
An employee of the DPR who wished to remain anonymous said the agency is performing a rigorous examination of the Oxitec plan to release its trademarked Friendly Mosquitoes, and the DPR will not issue its finding for several months. That means Oxitec and the DMVCD will not be able to start the test until 2023.
“We’re not going to be able to do it this year,” Debboun said. “The (mosquito) season already started.”
The female mosquitoes Oxitec has created need a source of the antibiotic tetracycline in order to reach maturity. Because the substance is not generally available in nature, the altered female aegypti are intended to die before they consume a blood meal and lay eggs.
The Friendly mosquitoes released will be male, and as they breed with the unaltered population, they will spread the altered gene.
According to the company, “Oxitec mosquitoes carry a self-limiting gene. When Oxitec male mosquitoes emerge and reproduce with invasive Aedes aegypti females, all offspring inherit a copy of this gene. The self-limiting gene prevents female offspring from surviving to adulthood.”
Oxitec plans to release millions of the males, and the company has already begun soliciting for volunteers willing to host a Friendly mosquito hatchery at their homes. The state has told Oxitec it must know exactly where it intends to release the modified insects.
Modified Mosquitoes Highly Sought
Debboun said DMVCD was selected out of 10 districts in the state that wanted the pilot program in their jurisdiction. Tulare County was chosen mainly because of its location and climate.
“It’s a combination of region – we were right in the center (of California) – and the (DMVCD) board wanted to go with the program,” he said. “I think the biggest thing is they (the modified mosquito release points) are central, they (the modified mosquitoes) can go north or south.”
Oxitec, which is based in Oxford, England, is already conducting a trial in the Florida Keys, a very humid region. Tulare County’s more arid climate will demonstrate how the Friendly bugs fare under less favorable conditions. The unaltered aegypti here are thriving.
The smaller cousin to the native mosquito is also known as the ankle-biter or the no-see-’em in states where the invasive species settled first before making its way west. Aegypti tend to bite more tender flesh than their larger relatives, and will bite the same victim repeatedly to get a full meal.
Aegypti are already insecticide-resistant, and Debboun said the Friendly mosquitoes offer a nontoxic approach to pest management.
“As a scientist, I’m always looking for new, innovative ways,” he said.
Critics Question GM Mosquitoes Friendliness
The plan to release billions of modified mosquitoes into the environment has been the subject of criticism. The group Friends of the Earth says a trial of the Friendly mosquitoes in Brazil led to a mixing of the GM mosquito’s genetic code with the local population, and the project did not reduce the number of aegypti in the test area.
Oxitec disagreed saying it “released non-biting male Aedes aegypti Friendly™ mosquitoes in the State of São Paulo, Brazil, and after 13 weeks suppressed up to 95% of Aedes aegypti mosquitoes. In May 2020, Oxitec received full commercial approval for this technology from Brazil’s national biosafety regulatory authority CTNBio after demonstrating the technology’s full safety for human health and the environment.
Friends of the Earth issued a statement at the time opposing the EPA’s approval of the use of the GM mosquitoes, claiming the testing will lead to unintended consequences.
“Scientists have found genetic material from GE (genetically engineered) mosquitoes in wild populations at significant levels, which means GE mosquitoes are not sterile. GE mosquitoes could result in far more health and environmental problems than they would solve,” said Dana Perls, Food and Technology Program Manager at Friends of the Earth, and a California resident. “EPA needs to do a real review of potential risks and stop ignoring widespread opposition in the communities where releases will happen.”
Oxitec says that Friends of the Earth misleads the public and that their statement is unfounded.
“There are over 100 independent peer-reviewed scientific publications on Oxitec’s technology. The EPA’s scientific and environmental assessments for included a review of over 4,500 pages of data and protocols, including 2,500+ pages of scientific peer-reviewed literature,” said the company.
The modified aegypti, however, are supposed to pass their genes to the endemic population in order to prevent the females that result from such breeding from reaching maturity.
The Friends of the Earth also claims the resulting offspring may be more robust and more able to spread disease in the environment. They point to a study from Yale University that shows the genes from the GM mosquitoes released in Brazil have irrevocably entered the local population. The study concluded:
It is unclear how this may affect disease transmission or affect other efforts to control these dangerous vectors. These results highlight the importance of having in place a genetic monitoring program during such releases to detect un-anticipated outcomes.
DMVCD says GM Mosquitoes Are Safe
In response, Debboun said the paper cited by Friends of the Earth has been retracted by some of its authors.
“Those are people who don’t have the correct data,” he said of the study’s authors. “I’ve read the articles and seen the science. The article was retracted.”
The editors of Nature, the scientific journal where the study was published in 2019, noted an “editorial expression of concern” regarding the article was published in May of 2020.
Concerns about the GM mosquitoes’ effects on the environment have not been dismissed, and that will be part of the research done in Tulare County if the DPR gives its OK to the plan.
“They (Oxitec) have to do their research,” Debborn said. “They need to review things.”
Meanwhile, the DMVCD is actively educating the public about the Oxitec insect release. The district has representatives at local events, such as home games of the Rawhide baseball team and at area farmers markets.
The district also hosts monthly informational webinars on the plan to release Oxitec’s mosquitoes and what residents can expect as a result. The next webinar is scheduled for 5 p.m. on Tuesday, June 21. Experts will explain the program during the webinar, then answer questions from the public.
Registration for the webinar is available at the DVMCD’s website, or by calling the district at (559) 732-8606.