How Zika spreads (and who’s to blame)
For the first time, the aggressive day-biting mosquito that can transmit the Zika virus has been discovered in Sacramento County, according to the Sacramento-Yolo Mosquito & Vector Control District.
“Now that we have found these invasive mosquitoes in our area, the goal is to control and limit their expansion,” said Sacramento-Yolo District Manager Gary Goodman. “We are mobilizing and responding quickly in order to protect the residents we serve.”
The Aedes aegypti mosquitoes can carry not only the Zika virus but also the debilitating chikungunya virus and the deadly dengue fever. Zika, though, strikes fear in many pregnant women because it can cause preterm births, miscarriages and congenital defects despite the fact that its symptoms are generally mild — fever, rash, conjunctivitis, muscle and joint pain, malaise or headache.
Dr. Dean Blumberg, an expert in infectious diseases at UC Davis Health, said pregnant women are most at risk of transmitting the illness to their unborn children late in their first trimester or early in their second one. While concerned that the Aedes aegypti mosquito has been detected in the local area, Blumberg said he felt he should put the discovery in perspective.
“This mosquito species – Aedis aegyptii – has been detected previously in California,” he said. “But it’s at a very low concentration, and so I’m also wondering if it’s going to reach a critical mass in order to transmit....If you get a critical mass of the mosquitoes, then you can have sustained transmission, and that would be very worrisome. I think there needs to be concern, but that needs to be balanced by the concentration of the mosquitoes.”
Goodman said the Sacramento-Yolo vector district is coordinating ground treatments to eliminate mosquitoes in neighborhoods along the northern Sacramento and Placer County line starting early Friday morning.
Blumberg urged residents to take precautions to stem mosquito reproduction and protect themselves against the insects. Wear insect repellent, he said, and cover arms and legs with clothing. At dusk, stay indoors or in screened areas.
The mosquito district has urged residents to look for stagnant water where mosquitoes can breed and drain it, no matter how small or how large the source. In the case of the immature Aedes aegypti mosquitoes found Thursday, Sacramento-Yolo vector district officials said, the insects were breeding in water left in a watering can at a residence and in a street storm drain — both sites in the Citrus Heights area.
The mosquito and vector district will send out technicians to help find the source of unusually high mosquito activity and help with abatement. District also recommended homeowners cover or repair holes in screens or windows that allow pests inside.
These measures also will help in the fight against the deadly West Nile virus, a mosquito-born illness that has so far killed two people and sickened 45 in California this year. Since 2004, 305 people have died of West Nile in California.
Zika virus was first discovered in Uganda’s forest in 1947, Blumberg said, but it wasn’t until 2014 when the disease exploded in the Americas that experts in infectious disease began to notice the correlation between the illness and birth defects.
Babies infected with the illness while in the womb have developed microcephaly, or a small head, as a result, Blumberg said. When the illness occurs later in pregnancy, he said, there is risk of premature birth or miscarriage. Occasionally, babies can be born appearing to have no sign of the congenital defects, Blumberg said, but they appear months or a year later.
Not everyone who gets Zika virus will get symptoms, Blumberg said, and the disease can remain active in semen long after men have recovered from the disease. Consequently, he said, it can be transmitted through sexual encounters by men who look healthy.
To date, though, there has been no local mosquito-born transmission of Zika in California, according to the state Department of Public Health. Since 2015, 729 Californians have returned from travels with the illness.
As of Aug. 9, insects that can carry the disease have been found in 15 counties, including Fresno, Merced, San Joaquin, and Stanislaus, but never as far north as Sacramento County.
While Zika grabs headlines, Blumberg said, both dengue (den-gay) fever and chikungunya (chicken-goo-nyuh) are quite serious illnesses. While chikungunya is not fatal, he said, it causes very severe bone and joint pain that can last months to years, and it can be debilitating.
As for dengue, Blumberg said, it is typically not serious the first time that someone gets it, but the second time, it can be quite severe.
“The second time, it’s a very high fever and then the flu-like symptoms of nausea, vomiting and muscle and joint pains,” he said, “and then you get the plasma that leaks out and the fluid accumulates, and those patients can have the respiratory problems, bleeding and really a lot of failure of organs. Those are the ones at risk of death.”