For about a year we’ve been hearing about a “new” virus affecting the health of infants: Zika. This Flavivirus originated in Uganda and was first isolated from rhesus monkeys in 1947. It was named after the Zika forest nearby. Like other infectious diseases, the ease of international travel has enabled this virus to spread out of Africa to the Americas and Asia. For parents and pediatricians, even as far from Brazil as Fort Collins, the news reports of neurologically damaged babies and escalating warnings from the CDC has caused tremendous concern.

What does Zika mean for us here in Colorado?

Two weeks ago, on the Pediatric Associates of Northern Colorado facebook page, I discussed another Flavivirus — West Nile Virus. While both are spread by mosquitoes, there are some important differences:

spread by Culex and Aedes mosquitos spread documented only in Aedes mosquitos*
persistent infection in many birds and mammals bit by infected mosquito Besides humans, only monkeys get infected
spreads from animals to humans commonly no evidence of animal to human spread
no sexual spread spreads through sexual contact and remains present in semen at least 2 months£

* Lab studies show Zika in Culex, but no known human cases from Culex (
£ one case report of Zika virus in semen at 6 months (

What all this means is that Zika virus can spread anywhere there are mosquitoes of the Aedes genus and so can be expected to eventually spread through the south, southwest and most of the midwest and eastern US. Fortunately, the seasonal variation in the US will limit the spread of the virus because mosquito populations fall when the weather gets cool. Also, at this time, few Aedes mosquitoes are in Colorado and the western US states (

Unfortunately, due to the ease of travel throughout the US as well as internationally, and the potential for human to human spread from sexual contact, we will likely see Zika virus in our state as well. As of 17 August 2016, there had been 2260 cases of Zika reported in the US — most from those who had traveled internationally or via sexual contact with those who had and in July health officials in Miami began to report spread of Zika domestically through infected mosquitoes there ( ).

What does Zika Virus do?

In older children and adults, Zika usually comes and goes without notice. Historically, only about 20% will exhibit any symptoms at all; and these are usually relatively minor: fever, joint pains, a rash and conjunctivitis (red eyes). Sometimes they may also have muscle soreness and headache. Rarely, an individual may develop a neurological disorder called Guillain-Barre Syndrome (GBS) which may cause a (usually) temporary paralysis that can affect the legs, torso and muscles used in breathing. (

In the unborn fetus, Zika can cause very severe brain malformations that cause the brain to be too small (microcephaly). Because this epidemic has occurred mostly in areas with fragmented and often insufficient healthcare systems, the specific incidence of various brain malformations remains unclear, but it appears that it is high, especially for mothers exposed in the first trimester of their pregnancy. The children with the more severe manifestations will have very limited physical and intellectual capabilities. (

What safety measures are recommended?

The CDC has issued a Level 2 travel alert which urges people traveling to high-risk countries and regions to take precautions to avoid mosquito bites. This means staying indoors at peak mosquito activity times (dusk), using mosquito netting and insect repellent. The also caution people who have recently returned from high-risk areas to use barrier contraceptives or avoid sex if pregnancy is at issue—for men who exhibit symptoms, the duration of this recommendation is 6 months; for others, 8 weeks is recommended.
Domestic travel is also potentially unsafe for pregnant women. In Florida, high-risk areas include Miami–Dade County, the city of Jacksonville, and Key West. In August, the CDC issued a travel alert recommending that pregnant women avoid these areas. In addition, border towns in southern and western Texas are at high risk of local Zika transmission and CDC officials predict that up to a quarter of Puerto Rico’s population might become infected with Zika this year. (
In the US, mosquito control is in the hands of local municipalities. In areas with concerning levels of Aedes mosquitoes pyrethrin and pyrethroid insecticides and various organophosphates, including naled, malathion, and in very rare instances chlorpyrifos are sprayed to reduce the mosquito population. Some of these agents are known to cause effects in humans and can be devastating to bees and other insects. Therefore, perhaps even more importantly, local authorities rely on public education campaigns encouraging homeowners to remove items that collect water outdoors, such as tires, buckets, planters, toys, birdbaths, flowerpot saucers, and trash containers so that mosquitoes have nowhere to breed.

Vaccine development

The Flaviviruses (Zika, WNV, Dengue, Yellow Fever, Japanese encephalitis) are tricky targets for vaccine development. Some of these viruses cause more severe effects in folks who catch it a 2nd time. Here, the antibodies developed from the prior infection amplify the inflammatory response upon re-infection in a phenomenon called antibody-dependent enhancement. Dengue is the best example of this where reinfection leads to massive immune-mediated hemorrhagic fever. In addition, there can be cross-reactivity of the antibodies to one of these viruses with others in the Flavivirus family. Virologists the world over are working to determine how Zika antibodies will act in humans. Will they provide protection or will subsequent infections be worse? Will Zika antibodies make infection with Dengue worse? Vice-versa?

Depending on the answers to these questions, we could see a vaccine in a couple of years or not at all.

If you’re worried about travel to areas that could have Zika the CDC website is updated frequently as recommendations change. You may also wish to talk over decisions about travel with an obstetrician or one of our pediatric providers at PANC.

Dr. Michael Hobaugh