Zika outbreak: Possible case from Florida mosquito investigated

CBC News | Posted: July 20, 2016 1:30 PM | Last Updated: July 20, 2016

Potential 1st homegrown case of Zika virus in continental U.S.

Health officials in Florida are investigating what could be the first Zika case spread by a local mosquito in the continental U.S.

The Zika infection was confirmed in lab tests, the U.S. Centers for Disease Control and Prevention and Florida's Department of Health said.

The state health department said it's investigating "a possible non-travel related cases of Zika virus in Miami-Dade County."

The patient is an adult woman who lives in Miami-Dade County, a health official familiar with the case told the Associated Press on condition of anonymity because the official wasn't authorized to reveal details beyond the statements released.

There has yet to be a case of local transmission by mosquitoes in the continental United States. More than 1,300 people in the U.S. and 149 in Canada have reported infections after traveling to a Zika outbreak area.

Brazil and Colombia have reported widespread Zika outbreaks. In most people, the virus causes only a mild illness that lasts a few days. The majority of those infected don't have symptoms, health officials say.

The concern is what the World Health Organization calls a scientific consensus that Zika virus can cause microcephaly — abnormally small heads in those born to women infected in pregnancy who may experience disabling developmental problems.

Several affected countries have also reported an increase in the number of cases of Guillain-Barré Syndrome, a neurological disorder.

U.S. mosquito control

Since late last week, mosquito control inspectors have been spraying to kill mosquitoes in the Miami area and emptying containers because the insects like to lay eggs in and around standing water.

They are also distributing Zika prevention kits and repellent, which are both strongly recommend for women who are pregnant or planning to be become pregnant.

Avoiding mosquito bites is the main way to protect yourself against Zika when travelling, the Public Health Agency of Canada says.

Reassuringly, researchers at University of Wisconsin report two common North American mosquito species (Culex pipiens and Aedes triseriatus) weren't able to transmit Zika virus to mice in the lab. Other mosquito species still need to be tested.

Someone who is infected with Zika can also spread it by unprotected sex.

In Utah, doctors and scientists are investigating how a man who cared for his dying father was infected with Zika. The virus is considered a contributing factor in the elderly patient's death. His son recovered.

Utah's unique case

Health officials say the infected caregiver had not had any recent travel to an area where Zika is being transmitted and did not have sex with an infected individual. The lack of those known risk factors makes the Utah case unique, health officials said.

In studies, the Zika virus can be detected in blood, saliva, semen, urine, breast milk and internal eye fluid that differs from tears.

"It's very important that people who are caring for critically ill patients avoid body fluids and carefully wash their hands after contact," said CDC's Dr. Denise Jamieson.

On the mosquito front, U.S. officials have predicted local outbreaks to begin as the weather warms, particularly in southern states such as Florida and Texas.

There are three steps in local transmission:

Someone who is infected with Zika while travelling and has high enough level of the virus returns home to the U.S.
The person then gets bitten by a local mosquito that is able to acquire and replicate the Zika virus.
The local mosquito then bites and infects someone else.

Experts with the CDC have previously said if local spread of the virus occurs in the U.S., it is not likely to be as widespread as in Latin America and Caribbean.

They point to what happened when Aedes mosquitoes spread dengue and chikungunya, cousins of Zika virus. Locally transmitted outbreaks of dengue occurred in Florida, Hawaii and Texas. Locally acquired chikungunya was previously reported in Florida, the CDC said.

In the continental U.S., greater use of air conditioning, window screens, mosquito control, and less densely populated areas than in Central and South America are all thought to lessen the likelihood of widespread outbreaks, CDC officials have said.

There are two other reasons why Zika epidemics are less likely to happen in Canada and the continental U.S., said Fiona Hunter, an entomologist at Brock University in St. Catharines, Ont., who travelled to Latin America to study the virus.

There, uncollected garbage fills with tiny amounts of water that acts as breeding sites for mosquitoes, Hunter said.

Secondly, "when someone is sick, there is no way to avoid being bitten. Homes are extremely porous (especially in the poorest areas which may be the hardest hit) and mosquitoes can come and go as they please, biting ill people and then passing it on to their neighbours," Hunter said in an email.

It's hoped that a vaccine will help control outbreaks. On Tuesday, a Canadian-led team announced it will start human trials of an experimental Zika vaccine.

It will be years before experimental Zika vaccines are produced and approved for clinical use.