Even as health authorities describe the symptoms of Zika infection in the general population as mild, a new surveillance study finds serious side effects are more common, and serious, than previously thought.
The Centers for Disease Control and Prevention (CDC) notes that many people infected with the Zika virus will have "no symptoms or mild symptoms" that may last a few days to a week. While it is well known that Zika causes severe defects when passed from mother to child in utero, less is known about how often, and how severe, symptoms are suffered by the general population.
A new study published in the Canadian Medical Association Journal (CMAJ) took a look at the full impacts of Zika infection on 1,118 travelers between October 2015 and September 2016 and found a "full clinical spectrum of acute Zika virus."
The Zika virus, currently thought to be carried by Aedes mosquitoes, gained a higher profile when it reached Brazil in 2013. Since that time, Zika virus has been found to spread by mosquito bite, through pregnancy, or between sexual partners. In the US to date, transmission of Zika from local mosquitoes has been reported in Florida and Texas.
Concern about the virus remains high. In Washington, DC, the CDC is offering retesting to more than 400 people, after lab workers in a city lab were found to have committed a small, but consistent error that led patients to believe they had not been exposed to the virus. So far, nine out of the 294 pregnant women retested have tested positive for Zika after originally being told they had not.
Research on Zika continues to explore its transmission, impacts, and treatment. A study published in the journal eLife uses data models to predict that 35 species of mosquitoes may be able to transmit Zika, including Culex pipiens, a mosquito with a range that includes the northern half of the US.
Against this backdrop of personal and public health concerns, scientists in the Canadian University Health Network analyzed a year of data collected from the Canadian Travel Medicine Network (CanTravNet) and found complications from infection with Zika virus could be underestimated.
The CMAJ study data was gathered at CanTravNet sites across Canada. On a larger scale, CanTravNet sites are part of the global surveillance network, GeoSentinal. Cases evaluated included Canadians that returned home sick, and non-Canadians who fell ill in Canada.
Physicians in CanTravNet follow a defined public health surveillance protocol and code data into the GeoSentinal platform. By analyzing the diverse group of travelers with standardized diagnostic methods, researchers developed the following findings:
- Of the 1,118 people evaluated, 41 (or 3.7%) had a Zika virus infection, 41 had dengue fever, and 23 had chikungunya. All of these are mosquito-borne viruses.
- Overall, Canada reported 330 cases of Zika virus infection during the 2015–2016 period, and the travelers in this study represented 12% of that total. As of February 2017, Canada reported a total of 473 travel-related cases of Zika, with three cases acquired through sexual contact.
- Of the 41 patients with Zika, 24 were women, and 19 were of child-bearing age, while three were pregnant.
- The virus was acquired by 40 individuals through mosquito bite, and one through sexual transmission.
- Regions where exposure occurred were the Caribbean and Central and South America. The patient who contracted the disease by sexual contact was through a partner who had been exposed to the virus in the Caribbean. Countries of concern include Columbia, Trinidad and Tobago, Nicaragua, Barbados, El Salvador, and Martinique.
- Infection occurred most commonly in the months of July, August, and December.
- Symptoms were not as mild as supposed. Rash and fever occurred in over 80% of the patients, and approximately half reported joint or muscle pain. More than 40 percent experienced headache. Two patients had symptoms of Guillain-Barré syndrome, a disorder of the nervous system. Other symptoms that occurred in just one or two patients included viral meningitis, conjunctivitis, and epididymitis, an inflammation of the tube on the back of the testicle that carries sperm.
- Dengue fever is a well-known, common cause of fever in travelers. Complications of dengue occur in between 1% and 20% of all cases. While dengue fever was diagnosed as much as Zika, researchers note "the rate of complications of acute illness was much higher among those with Zika than among those with dengue."
The take-home point of this study is that Zika infection may cause more severe complications than previously thought. "The common perception that Zika is associated with a very mild clinical course compared with dengue or chikungunya was not borne out in this small cohort," said researcher Dr. Andrea Boggild, Clinical Director of the Tropical Disease Unit at the University Health Network, in a press release.
When traveling in a region where Zika is active, take steps to protect yourself from Zika by preventing mosquito bites and using condoms to prevent sexual transmission. While the impact of Zika will change as populations develop immunity, the best way to avoid potential complications is to avoid Zika altogether.