Stock up on the bug spray and pet meds, California. Vets, insect experts and vector-borne disease researchers fear heavy winter rains will lead to an explosion of the mosquito, tick and flea populations. Diseases they spread can lead to irritation or even death for you and your pets.
‘Hell of a mosquito season’
"Yes, we are worried about mosquitos this year," said Nizza Sequeira, Public Information Officer for the Marin Sonoma Mosquito and Vector Control District. "When we have a year and receive so much rainwater as we did this past season, you're going to see a lot of areas that have been dry for a number of years collecting water."
She said that mosquitos only need a capful of water to breed.
"So our technicians at this point are out in force, checking fields, marshes, ditches, you name it, they're looking at it," she continued. "But one of our biggest concerns is what is in people's backyards."
Pots, trash, abandoned kids’ toys and play equipment can all collect water that can foster mosquito larvae.
"Our biggest concern right now is West Nile virus. And so that is spread by the bite of an infected mosquito," said Sequeira. "Generally, we tend to see the virus ramp up in the later during the summer months. But we have in the past detected the virus as early as spring."
About 1 in 5 people infected with West Nile virus develop a fever along with other symptoms like headache, body aches, joint pain, vomiting, diarrhea and a rash, according to the CDC. Fatigue and weakness can last weeks to months, and no medicine attacks the virus.
The CDC states that about 1 in 150 people develop a severe illness of the central nervous system, like encephalitis or meningitis. About 10% of those patients die.
West Nile virus doesn’t typically affect dogs or cats, but other mosquito-borne diseases are deadly to them. Heartworm disease is the main mosquito-borne issue, according to Erik Olstad, Assistant Professor at the University of California, Davis’ Veterinary Medicine Teaching Hospital.
"It's a devastating disease," Olstad said. "With all this new vegetation that's going to pop up with all this water that we have in our environment right now, I'm guessing we're going to see one hell of a mosquito season."
Infected mosquitos deposit small worms into an animal’s bloodstream.
"You can take a drop of blood and see the little tiny worms wiggle around in that blood sample. But over time, those worms mature into adult worms," he said and added that adults are large enough to be seen with the naked eye.
Babies take about six months to mature, and pets may not have symptoms while the worms grow.
"They will tend to accumulate in the chambers of the heart, and that pump no longer works effectively anymore," Olstad continued. "And so this worm can not only cause heart failure, but as the worms die, it can cause kind of an anaphylactic shock, reaction and thromboembolism and really horrible thing."
There is no approved treatment for cats except surgery on the heart and physically pulling the worms out.
Olstad injects a toxic medicine into infected dogs over three months for treatment. But dogs must be cage-bound the entire time to prevent a worm from being dislodged and entering the lungs.
Olstad said in rare instances, humans can be infected too.
The best protection is to keep pets on heartworm medications year-round, Olstad said. Even indoor pets are susceptible.
"How many times have you killed a mosquito in your house?" He asked.
Ticks become active during the rains. The blood-suckers thrive in years of higher humidity and precipitations, according to the Companion Animal Parasite Council. Olstad uses the CAPCvet.org site to track tick, mosquito and flea hot spots. And "conditions are ripe for reproduction," he said. Plus, the added vegetation gives ticks more opportunity to cling to a person or animal.
"And they want that vegetation. The little tick will be hanging off the branches with its little legs extended, just waiting for something fuzzy to walk past it," said Olstad "And they're really good at their job."
Marin/Sonoma vector control just started monitoring for ticks with tick-borne diseases for the year too. Vector control agencies across the world work to reduce or eliminate human contact with vectors such as ticks, mosquitos, rodents and birds that transmit disease.
"The start of the rainy season is what marks the start of active tick season here," Sequeira said. "If the wet weather were to persist late enough into the year, which would keep the ground level humidity up, that could possibly extend the tick season until later into the summer."
Ticks carry diseases as well, like Lyme disease, that can sicken animals and people. If not caught quickly, Lyme disease can cause lifelong complications and nervous system and organ damage.
Could this be a repeat of 2017 – the last drought-busting year in California?
California has been in drought since the start of this decade. The state is not officially out of drought yet. But, a series of atmospheric river storms dropped an average of over 11 inches of rain across every inch of the state in three weeks last month. San Francisco collected a quarter of the rain the city normally sees in a year in just one day during one of those storms.
The last drought-busting year was 2017, when a series of atmospheric storms rescued the state from a 5-year drought. Olstad was a practicing vet during that time and remembers seeing an increase in pests.
"We had a real bad year that year," Olstad said. "I definitely saw increases in the flea burden and the tick burden."
Marin/Sonoma Vector Control saw an uptick in birds killed by West Nile virus in 2017, too, compared to the recent years of drought. They found six times the number of infected birds in 2017 compared to either 2021 or 2022.
Flea for all
Fleas also thrive in damp environments. "Rain creates the perfect breeding ground for the insects that so often plague dogs, cats and people," stated the Wise and Wonderful Integrated Veterinary Center.
Fleas also love the grasses that are sprouting up across the state right now, according to Olstad.
Protect yourself and your pets
Medications can protect your pets. Covering up can protect people.
"The take-home message, really, when it comes to not just mosquito-borne illnesses, but personal protection against Lyme disease, is that it is a preventable disease," Sequeira said. "So it's extremely important that when you are out into a habitat, that you're taking the proper precautions."
She recommends these helpful tips to protect yourself against these insects:
- Wear long sleeves and pants in a tick habitat. Light-colored clothing makes it easier to see dark insects. You can treat clothing, boots and camping equipment with permethrin which can last through several washings.
- Use repellant on exposed skin with at least 20% DEET, picaridin, oil of lemon Eucalyptus or any other EPA-registered insect repellant. The EPA can help you find the product you need.