MADISON — Wisconsin has not seen even a trace of Zika virus, which federal health officials confirmed last week can cause serious birth defects, but that could soon change.
State health officials expect Wisconsin, one of only 10 states that have not reported a case of Zika in someone who traveled to affected countries in Latin America or the Caribbean, to get a travel-related case any day.
People are unlikely to contract Zika from a mosquito bite in the state this summer, but health officials can’t rule it out. The mosquitoes most likely to carry Zika generally are found in southern states, but the estimated range of one species reaches as far north as southern Wisconsin.
With warmer weather coming, authorities say people concerned about Zika should take steps to avoid mosquitoes and ticks known to be capable of carrying other pathogens, such as West Nile virus and Lyme disease.
“The risk of acquiring Zika from a mosquito bite in Wisconsin is really not a concern at this point,” said Karen McKeown, health officer for the state Department of Health Services. “But we encourage people to take precautions to avoid mosquito bites.”
Lyme disease and other tick-borne illnesses, such as anaplasmosis, ehrlichiosis and babesiosis, generally have been on the rise in Wisconsin in recent years.
Deer ticks in Wisconsin and Minnesota recently have been found to carry new species of Lyme and ehrlichiosis bacteria, which can cause fever, chills, muscle pain, headache, fatigue and other symptoms.
“It seems like every year we have more people getting infected with tick-borne disease and more kinds of tick-borne disease,” said Susan Paskewitz, a UW-Madison entomologist.
In confirming there is no doubt that the mosquito-borne Zika virus can cause severe birth defects such as microcephaly, a small brain, Dr. Sonja Rasmussen of the Centers for Disease Control and Prevention said pregnant women and others should wear long pants and long sleeves, or use repellent, and get rid of pools of standing water.
“It’s always important for pregnant women, and actually for everybody, to not get bitten by mosquitoes,” Rasmussen said. “It’s really important to make sure there isn’t standing water that is a breeding place near houses.”
At least 358 Americans, including 31 pregnant women, have developed Zika by traveling to affected countries such as Brazil, according to the CDC. In U.S. territories such as Puerto Rico, at least 475 cases have been acquired, including 58 in pregnant women.
Nobody has been infected with Zika from a mosquito bite occurring in the 50 states. But officials are closely monitoring states such as Hawaii, Florida, and Texas, which in recent years have had local outbreaks of similar diseases including dengue fever.
All states bordering Wisconsin have had Zika cases associated with travel, including 10 cases in Illinois and 12 in Minnesota. But of hundreds of samples tested from Wisconsin travelers, none has been positive.
“It seems almost inevitable that we will have a travel-related case,” McKeown said.
Pregnant women shouldn’t travel to affected countries, the CDC says. Anyone with an active infection can spread the virus through mosquito bites and sex, so the CDC advises them to avoid mosquitoes and abstain from sex or use condoms.
The mosquitoes most likely to carry Zika, yellow fever mosquitoes or Aedes aegypti, aren’t found in the upper Midwest, according to the CDC’s estimate of their range.
But another species, Asian tiger mosquitoes or Aedes albopictus, is thought to live in parts of southern Wisconsin and southern Minnesota, along with all of Iowa and Illinois.
However, the chance that those mosquitoes will transmit the virus to people in Wisconsin this year seems slim, Paskewitz said.
“It’s probably pretty close to zero; it might even be zero,” she said. “I wouldn’t say that if we were Florida.”
Paskewitz and others plan to set up traps for Asian tiger mosquitoes in southern counties this summer.
Unlike Culex mosquitoes that transmit West Nile, which are active at night and can be lured with light, carbon dioxide or smelly pools of water, the Aedes mosquitoes thought to carry Zika are daytime feeders. Traps for them, which could be set up by June, involve containers for laying eggs or other chemical lures, Paskewitz said.
Meanwhile, UW-Madison researchers continue to study Zika in rhesus macaque monkeys.
Since February, they’ve infected 11 monkeys with the virus to examine three questions: how long Zika persists in blood, urine and saliva; if infection protects against future exposure; and whether the stage of pregnancy in which infection occurs impacts the effects on offspring.
The bodies of nine non-pregnant monkeys have gotten rid of the virus in an average of about 10 days, said David O’Connor, a UW-Madison pathology professor who is part of the research team. But two pregnant monkeys infected in the first trimester have retained the virus so far for two weeks and more than a month, O’Connor said.
Their fetuses might be infected, re-seeding the mothers’ infections, or the immune systems of the mothers might be weaker because they are pregnant, O’Connor said.
“There is something unusual going on in pregnancy,” he said.
“It seems like every year we have more people getting infected with tick-borne disease and more kinds of tick-borne disease.” Susan Paskewitz, UW-Madison entomologist