The research, published in the Sept. 15 edition of PLOS Genetics, involved the study of Anopheles arabiensis, in Kilombero Valley in Tanzania. The mosquito is the primary vector of malaria in east Africa.
"We know that blood feeding preference among mosquitoes can be species specific,” said co-author and professor Greg Lanzaro, who leads the Vector Genetics Laboratory, UC Davis Department of Pathology, Microbiology and Immunology and is an affiliate of the UC Davis Department of Entomology and Nematology. “For example, there are mosquito species that specialize in feeding on amphibians or reptiles. We also know that many species are more catholic when choosing a meal and this can have important implications to human health—it's how some disease agents move between animals and humans.”
The publication is the work of a 13-member international team. Bradley Main, a researcher in the Vector Genetics Lab, is the lead author.
“Whether there is a genetic basis to feeding preferences in mosquitoes has long been debated,” said lead author Bradley Main, a researcher in the Vector Genetics Lab. “Using a population genomics approach, we have established an association between human feeding and a specific chromosomal rearrangement in the major east African malaria vector. This work paves the way for identifying specific genes that affect this critically important trait.”
Other co-authors, in addition to Lanzaro, are Anthony Cornel of the UC Davis Department of Entomology and Nematology faculty; researchers Yoosook Lee, Heather Ferguson, Travis Collier, Catelyn Nieman, Allison Weakley, all of the Vector Genetics Lab; Katharina Kreppel, Nicodem Govella and Anicet Kihonda of the Ifakara Health Institute, Ifakara, United Republic of Tanzania; and computer scientists Eleazar Eskin and Eun Yong Kang of UCLA.
In their summary, they wrote: “Malaria transmission is driven by the propensity for mosquito vectors to bite people, while its control depends on the tendency of mosquitoes to bite and rest in places where they will come into contact with insecticides. In many parts of Africa, where coverage with Long Lasting Insecticide Treated Nets is high, Anopheles arabiensis is the only remaining malaria vector. We sought to assess the potential for An. arabiensis to adapt its behavior to avoid control measures by investigating the genetic basis for its host choice and resting behavior. Blood fed An. arabiensis were collected resting indoors and outdoors in the Kilombero Valley, Tanzania. We sequenced a total of 48 genomes representing 4 phenotypes (human or cow fed, resting in or outdoors) and tested for genetic associations with each phenotype. Genomic analysis followed up by application of a novel molecular karyotyping assay which revealed a relationship between An. arabiensis that fed on cattle and the standard arrangement of the 3Ra inversion. This is strong support that An. arabiensis blood-feeding behavior has a substantial genetic component. Controlled host choice assays are needed to confirm a direct link between allelic variation within the 3Ra inversion and host preference.”
The publication, "The Genetic Basis of Host Preference and Resting Behavior in the Major African Malaria Vector, Anopheles arabiensis," is online at http://journals.plos.org/plosgenetics/article?id=10.1371/journal.pgen.1006303
Male Aedes aegypti mosquitoes infected with a bacterium, Wolbachia pipientis, are being released in Clovis, Fresno County, where this mosquito was discovered in June 2013. Although this mosquito is now found in California, there has been no locally transmitted case of the Zika virus in the state.
The project, to determine dispersal and survival, began Monday, May 10.
“The daytime-biting mosquito, which feeds predominantly on humans, has spread to at least seven counties since its discovery in Clovis,” said Cornel, a mosquito researcher and faculty member with the UC Davis Department of Entomology and Nematology and the UC Kearney Agricultural Research and Extension Center, Parlier.
“The biting nuisance and potential of the mosquito Aedes aegypti to transmit Zika, Chikungunya and dengue viruses in California is cause for concern,” he said. “Efforts to curb its spread and reduce populations have not been very effective. Control efforts have included educating the public to remove standing water (source reduction) insecticide barrier sprays and bacterial larviciding.”
The collaborative effort involves Steve Mulligan, director of the Consolidated Mosquito Abatement District, based in Fresno County; Stephen Dobson of the University of Kentucky; MosquitoMate Inc, (mosquitomate.com); and UC Davis. The researchers will evaluate the population suppressive ability of the novel sterile insect technique, which is part of a comprehensive vector management approach.
Only Aedes aegypti is targeted. “When the Wolbachia-infected male mosquito mates with non-infected females, the result is “cytoplasmic incompatibility, which causes the female to lay infertile eggs that will not hatch,” Cornel explained.
“This approach requires the release of tens of thousands of Wolbachia-infected males into residential neighborhoods where this mosquito is a nuisance,” the medical entomologist said. “Releasing large numbers of males increases the chance that an introduced male will mate with the native females.”
Although residents will notice increased numbers of male mosquitoes, male mosquitoes do not bite and cannot transmit disease. Both U.S,federal and State regulatory agencies have approved the technique for evaluation of effectiveness.
“This sterile insect technique was evaluated in 2015 in Los Angeles to suppress another invasive mosquito, Aedes albopictus,” Cornel said, adding that the results from that trial look promising.
The Zika virus, now spreading throughout the Western hemisphere, was first identified in Uganda in 1947 in rhesus monkeys, according to the World Health Organization. It was subsequently identified in humans in 1952 in Uganda and the United Republic of Tanzania. Outbreaks of Zika virus disease have been recorded in Africa, the Americas, Asia and the Pacific.
Despite the mosquito's invasion into new areas of the United States, there are no reported cases of locally transmitted Zika virus in California or in the contiguous United States, according to the Centers for Disease Control and Prevention. The cases have all involved travelers returning home from countries plagued with disease outbreaks.
“We can't predict how far this mosquito will spread in California,” said Cornel, noting that its range has expanded “south of Fresno to San Diego. The farthest site north is Madera in the Central Valley, but it's also been found in the more coastal area of Menlo Park in San Mateo.”
It's troubling that the mosquito is becoming more and more resistant to pesticides, said Cornel, who collects, rears and researches mosquitoes from all over the world, including the United States, Mali, Cameroon, Comoros, Tanzania, South Africa and Brazil.
“We have found that Aedes aegypti have insecticide resistance genes which likely explains why the use of ultra-low volume and barrier spray applications for control have not worked as well as expected.”
The event will take place in MU II (second floor) and is free and open to the public.
It's being held "to increase awareness among the general public about malaria, one of the world's oldest and deadliest diseases, as well as vector-borne problems at home in California," said medical entomologist Gregory Lanzaro, professor in the Department of Pathology, Microbiology and Immunology, UC Davis School of Veterinary Medicine.
Malaria "is a leading cause of death and disease in many developing countries, where young children and pregnant women are the groups most affected," the Center for Disease Control and Prevention (CDC) points out, citing these figures from the World Health Organization's World Malaria Report 2013 and the Global Malaria Action Plan:
- 3.4 billion people (half the world's population) live in areas at risk of malaria transmission in 106 countries and territories
- In 2012, malaria caused an estimated 207 million clinical episodes, and 627,000 deaths. An estimated 91% of deaths in 2010 were in the African Region.
The most vulnerable groups, CDC says, are young children, who have not yet developed partial immunity to malaria; pregnant woman, whose immunity is decreased by pregnancy, especially during the first and second pregnancies; and travelers or migrants coming from areas with little or no malaria transmission, who lack immunity.
The schedule for the UC Davis Malaria Awareness Day:
- 10 to 10:30 am.: Coffee/social/posters
- 10:30 to 10:50: "General Malaria Biology" by medical entomologist Gregory Lanzaro, professor, Department of Pathology, Microbiology and Immunology, UC Davis School of Veterinary Medicine.
- 10:50 to 11:20: Conducting Field Research in Rural Africa" by medical entomologist Anthony Cornel, associate professor, UC Davis Department of Entomology and Nematology and based at the UC Kearney Agriculture and Research Center, Parlier
- 11:10 to 11:30: "Malaria Parasites in the Mosquito" by molecular biologist Shirley Luckhart, professor, UC Davis Department of Medical Microbiology and Immunology and an adjunct professor in the Department of Entomology and Nematology
- 11:30 to 11:50: "Mosquito-Borne Viral Diseases" by medical entomologist Chris Barker, assistant adjunct professor and assistant research scientist, UC Davis Department of Pathology, Microbiology and Immunology
- 11:50 to 12:10: "Disease Transmission by Non-Mosquito Vectors" by epidemiologist/veterinarian and disease ecologist Janet Foley, professor, UC Davis Department of Medicine and Epidemiology
- 12:10 to 1:30: A free lunch will be provided, but reservations must be made by April 21 to Youki Kevin Yamasaki at firstname.lastname@example.org.
“It's an issue of great concern, especially as current control methods do not appear to be working well,” said Cornel, who does research on the mosquito in Clovis, Fresno County, where it was discovered in June 2013. Simultaneously, the insect was found in the cities of Madera and San Mateo.
“This ongoing widespread invasion and establishment proves that this is no longer a regional issue and has affected many cities and towns in California,” he wrote Feb. 8 in F1000 Research, http://f1000research.com/slides/5-149.
But Cornel is optimistic that the pest management intervention strategies and surveillance and control tactics now underway will help control its spread. Infected Aedes aegypti can transmit dengue, yellow fever, Zika and chikungunya viruses.
The Zika virus, now spreading throughout the Western hemisphere, is an emerging mosquito-borne virus that was first identified in Uganda in 1947 in rhesus monkeys, according to the World Health Organization. It was subsequently identified in humans in 1952 in Uganda and the United Republic of Tanzania. Outbreaks of Zika virus disease have been recorded in Africa, the Americas, Asia and the Pacific.
Despite the mosquito's invasion in parts of the United States, there are no reported cases of locally transmitted Zika virus in California or in the contiguous United States, according to the Centers for Disease Control and Prevention. The cases have all involved travelers returning home from countries plagued with disease outbreaks.
Cornel works with the Consolidated Mosquito Abatement District, based in Fresno County, to tackle the spread of the mosquito there. The district covers 1,058 square miles, including part of Kings County.
How far north in California will the mosquito, commonly known as yellow fever mosquito, spread?
“I don't want to exclude the possibility that it may spread as far north as Sacramento,” said Cornel, who collects, rears and researches mosquitoes from all over the world, including the United States, Mali, Cameroon, Comoros, Tanzania, South Africa and Brazil. “We need to see if it overwinters as eggs or adults or both.”
It's troubling that the mosquito is becoming more and more resistant to pesticides, Cornel said. “We have found that the Aedes aegypti have insecticide resistance genes which likely explains why their ultra-low volume and barrier spray applications have not worked as well as expected.”
At Clovis, Cornel and his colleagues trap mosquitoes in gravid or ovitraps; study overwintering and flight dispersal; and employ mark-release-capture trials to estimate dispersal and population size, needed to plan biological (Wolbachia) and chemical auto-dissemination control strategies. They also engage in “recruiting” mosquitoes to kill other mosquitoes. “We have mosquitoes spread insecticides for us, that is, we turn them into mosquito-control workers through the use of insect growth regulators and biopesticides.”
Their 27-slide document, “Surveillance and Control of Aedes aegypti Mosquito in Clovis, Calif.,” published in F1000 Research details their research with text and maps. It is work of Cornel and Yoosook Lee of UC Davis; Stephen Dobson of the University of Kentucky; Corey Bansfield of MosqMate Inc. and Jodi Holeman, Mark Amireno, Charles Smith and Stephen Mulligan III of the Consolidated Mosquito Control District. In the document, Mulligan, director of the Consolidated Mosquito Control District, describes Aedes aegypti as “the rat of the mosquitoes.”
The California team works with University of Kentucky scientists to develop novel control strategies. One trial involves coating male mosquitoes with insect growth regulators, which are passed on to the females. Males are also infested with a biopesticide or “a good bacteria-like organism,” Wolbachia. “The male transfers it to the female, which affects the ovaries and negatively affects immature development,” Cornel explained. “It's not new, but it's not been employed in large trials.”
Regarding flight dispersal, Cornel has found that “males can fly well over 200 meters in one night from their breeding site. We previously thought it was no more than 60 to 100 meters.”
“The Aedes aegypti fly predominantly during cooler periods of the day,” the medical entomologist said. “When it's too hot, they hang around the shade.” When residents walk at dusk, both male and female mosquitoes can follow them. “Only the females bite but the males will hang around your ankle waiting for the females to arrive.”
The researchers target mosquito breeding sites, primarily yard drains. “Despite the drought and the elimination of visible bodies of water, such as bird baths, pet bowls and flower pots, there's a major issue: yard drains,” Cornel said. “Yard drains installed in new home developments empty into the gutter or street and are cryptic breeding sites for mosquitoes.” He speculates that these mosquitoes are breeding underground.
“These drains are not easily accessible and we can't see the mosquitoes,” Cornel pointed out. “We need to blow out the water and plug these yard drains to eliminate these breeding sites.” He suggests that cities everywhere address this public safety issue and “redesign the yard drains.”
Cornel works with the Consolidated Mosquito Abatement District in setting gravid or “killing traps” in the front yards of homes in Clovis. The traps, which look like five-gallon buckets, contain orchard grass and water. “When the orchard grass decomposes, it releases a plume of chemicals that attracts female Aedes aegypti to lay their eggs in,” Cornel said. A screen prevents them from reaching the water to lay their eggs. The insects adhere to black sticky paper.
It's crucial for the public to become involved, Cornel said. “We have to focus on public education. We have to get the message across to eliminate mosquito breeding sites. We can't go to every house. We must rely on the public to eliminate the breeding sites.”
It's possible—but he hopes not—that what is now a “mosquito nuisance” will result in a disease outbreak.
- Anthony Cornel: Mosquito Man UC Davis Department of Entomology and Nematology
- Anthony Cornel, Kearney Agricultural Research and Extension Center
- Yoosook Lee, UC Davis Department of Pathology, Microbiology and Immunology, School of Veterinary Medicine
- F1000 Research
- Traps Tested in Clovis (UC ANR)
- Aedes aegypti, California Department of Public Health, Aedes aegypti
- Consolidated Mosquito Control District, based in Fresno County
Carlson, to speak on avian (bird) malaria, was one of 20 presenters--five from each specialty section--selected by ESA officials to deliver a Premier Presentation. Her specialty section is Medical, Urban and Veterinary Entomology. A two to three-minute video featuring her and her work will be posted online following her presentation.
Carlson will discuss the work she completed at UC Davis under the tutelage of her major professor, medical entomologist Anthony Cornel, a member of the UC Davis Department of Entomology and Nematology faculty who is headquartered at the Kearney Agricultural Research and Extension Center, Parlier. While at UC Davis, Carlson was based in the lab of William Reisen, then a graduate student advisor with the Department of Entomology and Nematology and director of the Center for Vectorborne Diseases, School of Veterinary Medicine. Reisen, now retired, also served on her dissertation committee.
“I will present the avian malaria disease risk predictions for the endemic avian populations on Socorro Island, Mexico, and in the subarctic region of Alaska,” she said. “Using California-based vector competence studies as a guideline, I will discuss how vectors are structuring Plasmodium-host relationships by serving as both a compatibility filter and as an encounter filter. These are extremely important entomological considerations that must be included in a wildlife conservation and management plan, failure to neglect this component in disease risk assessments could result in the collapse of a fragile endemic avian population.”
While at UC Davis, Carlson received a number of honors, including the William Hazeltine Memorial Research Fellowship Awards for four years, 2011 to 2014; the Henry A. Jastro Shields Research Award, 2012 to 2014; and the UC Davis McBeth Memorial Scholarship, 2011 to 2012.
Her current goals are four-fold:
1. To continue conducting research in the field of human and animal disease.
2. To apply her knowledge in vector-borne diseases to help improve human, animal and ecosystem health.
3. To participate in collaborative research on naturally occurring human and animal disease,
4. To learn new molecular techniques that would aid in the identification of re-emerging and novel pathogens.
Carlson received her bachelor of science degree in zoology in 2006 from Colorado, State University and her master's degree in biology in 2008 from San Francisco State University.