After confirming Zika virus’ presence on St. Croix last Friday, local health officials are uncertain about how the outbreak will unfold in the territory.
There’s only been one confirmed case so far, but Zika’s possible link to developmental defects in newborn babies underscores the danger of its spread.
Looking at previous outbreaks of mosquito-borne diseases can offer hints of what could happen, but their varying pathologies make them difficult to compare. The territory’s geographical situation and environmental conditions do offer some clues about how the virus got here and why it’s spreading.
Past Mosquito-borne Disease Outbreaks
To date, dengue, chikungunya and Zika are the only known mosquito-borne diseases that have affected the territory.
Dengue was first reported in the Caribbean in the early 1900s and has likely been in the territory for decades, with the last outbreak occurring here in 2012. Chikungunya is a newcomer, having arrived in the Virgin Islands in July 2014.
The territory’s epidemiologist, Dr. Esther Ellis, said the 2014-2015 chikungunya outbreak peaked for about two months, infecting a confirmed number of 405 people, but that new cases tapered out within about a year. She added that detailed incidence reports don’t exist for past dengue outbreaks but will be kept going forward.
Even though the same mosquito type spreads Zika and chikungunya, Ellis said it’s difficult to predict how long the Zika outbreak will last here.
Zika and chikungunya can’t be reliably compared, since their pathologies are so different. According to the Centers for Disease Control, only one in five people experience symptoms with Zika, and the virus stays in the blood for less than five days, leaving a small window of time for mosquitoes to bite infected people.
Twenty-five percent of people show symptoms when they get dengue, while 75 percent of people who contract chikungunya do. These viruses stay in the blood for seven to ten days, a significantly longer time than Zika does.
Other vector-borne diseases are present in the Americas, such as West Nile Virus and leishmaniasis, which is spread by sandflies, but at this point they aren’t thought to be a threat to the territory. Ellis said the type of mosquito that spreads Malaria isn’t present in the region and its range is unlikely to change.
In the Virgin Islands, only the aedes aegypti mosquito carries viruses that can be passed on to humans. This mosquito species is present in every country in the Americas except for Canada, meaning Zika could spread a great deal more.
The Virgin Islands has already sent samples of suspected cases from all three islands for testing at the CDC in Atlanta, but results could take as long as two weeks to receive.
The fact that there’s a confirmed case of Zika in the territory and there haven’t been any recent ones for dengue or chikungunya makes local health officials think Zika is the likelier cause of the suspected cases.
Geographical and Environmental Factors
From a geographical perspective, small islands like those that make up the territory aren’t necessarily more or less susceptible to outbreaks of mosquito-borne disease.
Ellis said that the territory’s warm temperatures and wet environment are what make it conducive to mosquito reproduction.
"An outbreak could occur if local conditions are warm enough to permit mosquito biting activity, leading to an increase in the number of infected people and infected mosquitoes," Ellis said.
When Puerto Rico reports a case of mosquito-borne illness, it becomes a red flag for the Virgin Islands, since travel between the two is common. Past outbreaks of dengue have correlated with Puerto Rico due to similar rainfall seasons, since mosquitoes need water to breed and their population booms a few weeks after rainfall.
Since there’s only been a single outbreak of chikungunya and the Zika one is just beginning, health officials can’t yet link them to rainfall patterns. Typically there aren’t outbreaks this time of year, but more frequent travel and unexpected high levels of rainfall could be contributing to mosquito reproduction, Ellis explained.
The outbreaks of chikungunya and Zika in the Virgin Islands, however, were preceded by cases in Puerto Rico, an indication of frequent travel between the two places.
Increased travel is the driving force behind Zika spreading throughout the Americas, and to the Virgin Islands specifically, since an infected person must travel here and be bitten by an aedes aegypti mosquito that then bites another person.
Links to Birth Defects
As Zika’s symptoms are similar to but milder than dengue’s, the most alarming threat is its probable link to microcephaly in newborns, a rare condition that causes babies to be born with smaller than normal heads that in turn leads to intellectual disabilities.
To date no other mosquito-borne virus has been known to have such lasting prenatal developmental effects. With no vaccines or treatments, President Barrack Obama is urging medical professionals to work quickly to address the deficiency.
Countries across Latin America, including the governments of El Salvador, Brazil and Colombia, have issued notices urging women to delay pregnancy until the Zika outbreak is over.
So far, the Virgin Islands Department of Health has not issued such warnings, but Ellis said she would encourage women who are trying to conceive to wait. She noted that it will take time to determine what the exact cause of microcephaly is, though Zika is the likeliest suspect.
“It will be many more months to a year, since studies are getting started now to follow pregnant women, and this timeline would take at least nine months from start to finish,” Ellis said.
Zika was first found in Uganda in the 1940s and has since become common throughout parts of Africa and Asia, but it didn’t hit the Americas’ mainland until May 2015 when it popped up in Brazil. If the virus caused microcephaly in the past, it previously went unnoticed.
Tourism Commissioner Beverly Nicholson-Doty is aware that health warnings could impact visitor arrivals. With imported Zika cases reported in the U.S. mainland, the spread of the disease is now on more people’s radars.
“We are following the CDC guidelines and communicating this to our tourism partners. We are also working on a rack card that will be given to visitors on arrival similar to what was distributed at the height of chikungunya,” Nicholson-Doty said.
To prevent a full-blown outbreak of the disease, Ellis said people should prevent mosquito bites by staying indoors or wearing long-sleeves, as well as getting rid of mosquito breeding sites, since the aedes aegypti mosquito likes clean water and can breed in containers that are as small as water bottle caps.
“We have conducted trainings at both hospitals and have been working with providers to identify the symptoms of the Zika virus. We also want to stress to all pregnant women to seek medical attention in the event that you are experiencing any symptoms and use all means to prevent mosquito bites,” Ellis said in a press release issued Friday by the V.I. Department of Health.