Zika is establishing a foothold in the Commonwealth of Puerto Rico, which has ongoing transmission of the virus and spread is projected to increase, the CDC reports.
The CDC recently reported 30 confirmed cases in Puerto Rico, only one of which was travel-related.1 Because the most common mosquito vector of Zika virus, Aedes aegypti, is present throughout Puerto Rico, Zika virus is expected to continue to spread throughout the island. Past spread of two other mosquito-borne viruses, dengue and chikungunya, do not bode well for containing Zika in Puerto Rico as well as the U.S. Virgin Islands and American Samoa.
“There have been case reports of local transmission in all three territories,” CDC director Tom Frieden, MD, MPH, said in recent Congressional testimony. “Furthermore, recent outbreaks of mosquito-borne dengue and chikungunya suggest that Zika virus may spread widely in those areas. We need to be fully prepared, especially as the spring and summer months arrive. We are particularly concerned about Puerto Rico and the U.S. territories that may experience substantial spread of Zika. For comparison, more than 80% of adults in Puerto Rico have been infected with at least one strain of dengue, and about a quarter have been infected with the more recently introduced chikungunya virus.”
The cases in Puerto Rico include one pregnant woman and a 37-year-old old man who developed Guillain-Barre syndrome after acquiring Zika. The woman was in her first trimester of pregnancy had symptoms of body and joint pain, rash, conjunctivitis, and nausea. Her obstetrician provided counseling regarding risks to her fetus and recommended clinical follow-up with CDC interim guidelines.
The man developed a rash, which resolved in two days, but the next day he reported a tingling sensation in his hands and feet, followed by progressive weakness in limb muscles and uncontrolled fluctuating hypertension. He was hospitalized with ascending paralysis and responded to treatment with intravenous immunoglobulin.
Overall, three (10%) of the patients were hospitalized, a rate “higher than expected on the basis of previous reports,” the CDC reported. Most of the patients resided in eastern Puerto Rico or the San Juan metropolitan area. The most frequently reported signs and symptoms were rash (77%), myalgia (77%), arthralgia (73%), and fever (73%). Approximately 25% of patients sought healthcare, suggesting there could be more Zika infections with mild symptoms that were not captured in surveillance.
Clinicians in Puerto Rico and other clinicians evaluating patients with recent travel to Puerto Rico should report all cases of suspected Zika virus disease to public health authorities. Residents of and visitors to Puerto Rico should strictly follow steps to avoid mosquito bites including using air conditioning or window and door screens when indoors, wearing long sleeves and pants, using permethrin-treated clothing and gear, and using insect repellents.
PANDEMICS TO COME
Ecological and climate change in an increasingly interconnected world mean that mosquito-borne diseases such as Zika virus can appear in areas they hadn’t been before, and unfortunately we can expect novel infectious diseases to continue emerging, said Ariel Pablos-Mendez, MD, assistant administrator of the Bureau for Global Health in the U.S. Agency for International Development.
“If there is anything that Zika has already taught us, it is that there will be a next time — another pathogen that spills into humans with the potential to amplify and spread beyond borders,” he said at a recent Congressional hearing on the outbreak.
“Zika, like MERS, SARS, avian influenza, and Ebola all point to a [new] landscape where the interaction between humans, animals, and vectors is vastly different and constantly changing,” Pablos-Mendez said. “These rapidly changing dynamics are fundamentally altering the emergence patterns of zoonotic and vector-borne diseases, and increase the likelihood of new spillover and amplification opportunities for these pathogens into human populations.”
In February 2014, the U.S. joined with other countries to launch the Global Health Security Agenda (GHSA). GHSA is an international effort to build capacity to prevent, detect, and respond to infectious diseases, and to build political commitment to ensure appropriate action is taken as “high-consequence pathogens” continue to emerge, he said.
The Zika virus was first discovered in monkeys in Uganda in 1947, and is now considered endemic to Africa and Southeast Asia. Zika is a flavivirus like dengue and yellow fever, with all primarily transmitted by A. aegyti mosquitoes. With Zika previously unreported in the Americas, the virus is exploding in a large population with little existing immunity. Those infected should develop immunity to subsequent infections, but until a vaccine and effective treatments are developed, Zika must be largely prevented by avoiding mosquito bites and killing back the vector population.
There are calls to eradicate mosquitoes completely, though some warn of unintended consequences in the ecosystem even if it were possible. Last year, Brazil released genetically modified mosquitoes designed by Oxitec Ltd. in the U.K., reducing A. aegyti by 80% in the targeted experiment area. Unfortunately, mosquito populations can rebound so quickly it would take a massive ongoing effort to really have an effect on the prevalence of vector-borne infectious diseases. The possibility is there though to use so-called “gene drive” technology to create mosquitoes that will pass a desired trait on to future generations, either continuing a cull or creating some modified effect like the inability to carry the malaria parasite.
With these possibilities still a few years away at best, we are faced with a formidable adversary. The A. aegyti mosquito that carries Zika seems as if it was designed to spread disease, biting at all hours and needing only small amounts of water — a cup here, an old tire there — to lay eggs.
“The Aedes aegypti is an aggressive mosquito,” Frieden said. “It bites four or five people at one blood meal. It bites relatively painlessly, so you don’t swat it and kill it. And it is ideally suited to the crowded urban environment, where there is standing water that can be a small as a drop of water in a bottle cap where it can breed. And where it is challenging to get rid of or avoid, because it bites all day long. Not just at dawn and dusk. So everything that we’ve seen about not just Zika, but dengue and chikungunya, suggests that this is the overwhelming cause of transmission.”
There also is some question and certainly concern whether A. aegypti’s cousin, Aedes albopictus — with a habitat that extends farther north in the U.S. — could become a Zika transmitter. The combination of these threats and a population of millions of people with no existing immunity raises a virtual “perfect storm” scenario, so it is worth repeating that 80% of these infections should be asymptomatic and the others self-limiting.
- Thomas DL, Sharp TM, Torres J, et al. Local Transmission of Zika Virus — Puerto Rico, November 23, 2015–January 28, 2016. MMWR Early Release 2016;65:1-6.