July 14, 2023
MCHD works with University of South Alabama to identify mosquito threats
MOBILE, Ala. — The Mobile County Health Department (MCHD) was formed in 1816 to help deal with the Yellow Fever outbreak that was devastating to local residents. During the epidemic of 1819 (the year of Alabama’s statehood), Mobile recorded approximately 430 deaths out of a population of about 1,000.
There were many suggestions at the time on how the disease was transmitted, but it was later determined to be spread by mosquitoes. So, from the beginning MCHD’s Vector Services has proven to be a valuable defender of the public’s health. A vector is any insect, rodent, or animal capable of harboring or transmitting diseases to humans.
“We have a multi-prong approach to mosquito-borne illness surveillance,” said Dr. Kevin Philip Michaels, Health Officer of Mobile County. “We have our sentinel chicken program, mosquito identification and testing, human surveillance of mosquito borne diseases, along with prevention and education of the community. We also use fish, larvicides and spraying to control them.”
At the end of June, a mosquito captured in one of the 28 traps maintained by MCHD inspectors tested positive for Eastern Equine Encephalitis Virus (EEEV). This case was the result of a collaboration with the University of South Alabama (USA) that began in 2018.
Jonathan O. Rayner, Ph.D., is an Assistant Professor in USA’s Department of Microbiology & Immunology and the Director of the Laboratory of Infectious Diseases. He said when he moved to Mobile in 2017 that he was impressed to learn MCHD had a sentinel chicken program.
“I actually reached out to MCHD myself to see what efforts were in place,” Dr. Rayner said. “I was probably the only person in the world to be excited about this.
“I already knew that MCHD had established its sentinel chicken program. I wanted to know what other methods they used to support the mosquito-borne infectious disease surveillance program.”
It was at this point that Dr. Rayner suggested a new procedure that could help.
“I started taking about molecular surveillance on the actual mosquitoes,” Dr. Rayner said. “It is a very common technique used in various states. Some places do chickens; some places do both.”
After a grant was awarded to help fund the project, MCHD began supplying mosquito samples to USA.
“MCHD sets up traps around the county,” Dr. Rayner said. “Once they collect the traps, the mosquitoes are sorted by species. That gives us an idea of what vector species are present.
“Then specific species are subjected to nucleic acid extraction. Next, they are screened using a Polymerase Chain Reaction (PCR) technique to detect the genome of the virus. The whole process takes about five to six hours once the mosquitoes are received in the lab.”
Mobile County has more than 50 species of mosquitoes. The genera most analyzed for viruses are Culex and Aedes. In 2022, more than 40,000 mosquitoes were collected by MCHD traps.
“We screen the Culex mosquitoes for EEEV, Saint Louis Encephalitis Virus, and West Nile Virus,” Dr. Rayner said. “These are maintained in nature between birds and mosquitoes. Thus, combined with the sentinel chickens, we have greater opportunity to identify the presence of the virus before we have human cases.
“We screen the Aedes mosquitoes for Dengue Virus, Zika Virus, and Chikungunya Virus. These are maintained in nature between primates, including humans, and do not infect birds, so the sentinel chicken program is not effective there. The risks for those viruses are significantly lower because we don’t have a lot of primates other than people in Mobile to sustain transmission.”
The USA program has identified viruses in several mosquitoes over the years. This includes a mosquito analyzed in 2019 with EEEV, two in 2020 with West Nile Virus, one in 2021 with EEEV, and three in 2023 with EEEV (one was PCR confirmed while the other two were listed as “weak positive”).
“Mosquitoes are collected and sorted by date and location to determine the abundance of species capable of transmitting pathogens to humans,” Dr. Rayner said. “Results from these activities together are used by the county to further direct and refine established abatement programs intended to reduce mosquito populations and minimize human exposure to the pathogens.”
Dr. Rayner said it is vital for all agencies to be focused on monitoring the mosquito population.
“It is really important to emphasize that we are a port city,” he said. “That provides an opportunity for new vectors and new viruses to be introduced.
“Global warming also has had a significant impact. More vectors are introduced and thrive for longer periods of time. Mosquitoes usually die off when cold. So, you have a greater chance for yearlong transmission.”
Local investigators also have to be prepared for other diseases not normally found here. “Malaria cases have recently been reported in South Florida,” Dr. Rayner said. “While we are not looking for malaria here, we have recorded the presence of the Anopheles mosquito which can transmit malaria. We have to be vigilant.”
A new online portal is now available to help the public request assistance from Vector Services and receive feedback on their request to deal with mosquitoes or rodents. To learn more about the department, you may visit https://mchd.org/vector-control. From there, you can find a link and a QR code to access the new online portal for ordering services. The telephone numbers for those without internet access are 251-690-8124 for Mosquito Control and 251-690-8819 for Rodent Control.
“Kudos to MCHD for setting up these efforts and being proactive for protecting the citizens here,” Dr. Rayner said. “Local efforts are really aimed at dealing with mosquitoes. Once a vector reaches a certain threshold, MCHD works to reduce it.”