The World Health Organization (WHO) declared last week that the Zika virus is an international health emergency, calling it an "extraordinary event" due to its apparent association with congenital malformations and neurological complications reported in the Americas region.
The disease, a single-stranded RNA virus of the Flaviviridae family, genus Flavivirus, is transmitted through the bite of infected daytime-active Aedes species mosquitoes (the same mosquitoes that spread dengue and chikungunya viruses).
According to CDC, the mosquito vectors typically breed in domestic water-holding containers; they are aggressive daytime biters and feed both indoors and outdoors near dwellings. Non-human and human primates are likely the main reservoirs of the virus, and anthroponotic (human-to-vector-to-human) transmission occurs during outbreaks.
Zika Virus History
Zika virus is not a new strain but was first identified in Uganda in 1947 in rhesus monkeys through a monitoring network of sylvatic yellow fever. It was subsequently identified in humans in 1952 in Uganda and the United Republic of Tanzania.
Zika virus disease outbreaks were reported for the first time in the Pacific in 2007 and 2013 (Yap and French Polynesia, respectively). Before 2007, there were only 14 documented Zika cases worldwide.
In May 2015, the situation changed drastically when the Pan American Health Organization (PAHO) issued an alert regarding the first confirmed Zika virus infection in Brazil. The outbreak led to reports of Guillain-Barré syndrome and pregnant women giving birth to babies with birth defects and poor pregnancy outcomes.
The virus has transformed into a worldwide pandemic that is circulating in Africa, the Americas, Asia, and the Pacific.
No locally-transmitted Zika cases had been reported in the continental United States — only cases related to returning travelers — until last week when, according to a news report, health officials in Dallas said a woman there contracted the Zika virus through sexual contact, making it the country's first confirmed case of the virus during the current outbreak. In medical literature, there has only been one other case of Zika transmitted sexually.
Zika Virus Symptomatology
The virus — known as Zika fever, Zika, or Zika disease — typically manifests mild symptoms that include the acute onset of fever with maculopapular rash, arthralgia, and conjunctivitis. Other commonly reported symptoms include myalgia and headache. Generally, symptoms last for several days to a week. Severe disease requiring hospitalization is uncommon, and case fatality is low.
Zika Virus Diagnosis and Reporting
Preliminary diagnosis is based on the patient’s clinical features, places and dates of travel, and activities, said CDC. Laboratory diagnosis is generally accomplished by testing serum or plasma to detect virus, viral nucleic acid, or virus-specific immunoglobulin M and neutralizing antibodies.
Now that the Zika virus is a nationally notifiable condition, health care providers are encouraged to report suspected cases to their state or local health departments, to facilitate diagnosis and mitigate the risk of local transmission. State health departments are encouraged to report laboratory-confirmed cases to CDC through ArboNET, the national surveillance system for arboviral disease.
Zika Virus Treatment
No specific antiviral treatment or vaccine is available for Zika virus. Treatment is generally supportive and can include bed rest, rehydration, and the use of analgesics and antipyretics.
Because of similar geographic distribution and symptoms, patients with suspected Zika virus infections should be evaluated and managed for possible dengue or chikungunya virus infection. Aspirin and other non-steroidal anti-inflammatory drugs (NSAIDs) should be avoided until dengue can be ruled out to reduce the risk of hemorrhage.
Zika Virus Association with Neonatal Neurologic Conditions
Since Zika arrived in Brazil last year, more than 4,000 cases of microcephaly have been reported — a twentyfold increase from previous years, said Vox Science & Health.
"The virus been found in the amniotic fluid of pregnant women carrying babies with the birth defect, and even in the brains of babies with microcephaly who died within 24 hours of being born," Vox said.
Researchers are still working to confirm the link, to determine if there may be other causal factors. It could take six to nine months, however, before science proves or disproves any connection between the virus and babies born in Brazil (or elsewhere) with neurologic abnormalities.
Zika Virus: Fourth in a Succession of Arthropod-borne Diseases
Aside from its potential effect on infants, a study in The New England Journal of Medicine by Drs. Anthony S. Fauci and David M. Morens said that there is more to this otherwise innocuous virus than meets the eye:
"The explosive pandemic of Zika virus infection occurring throughout South America, Central America, and the Caribbean and potentially threatening the United States is the most recent of four unexpected arrivals of important arthropod-borne viral diseases in the Western Hemisphere over the past 20 years. It follows dengue, which entered this hemisphere stealthily over decades and then more aggressively in the 1990s; West Nile virus, which emerged in 1999; and chikungunya, which emerged in 2013."
In the study, Fauci and Morens questioned whether the successive migrations of these viruses were unrelated or reflected new patterns of disease emergence. Further, they attributed the spread of the disease to humanity's disruption of the ecological balance:
"[I]n our human-dominated world, urban crowding, constant international travel, and other human behaviors combined with human-caused microperturbations in ecologic balance can cause innumerable slumbering infectious agents to emerge unexpectedly."
The authors concluded the study with this rather ominous statement:
"[A]rboviruses continually evolve and adapt within ecologic niches that are increasingly being perturbed by humans. Zika is still a pandemic in progress, and many important questions about it, such as that of teratogenicity, remain to be answered.”
Is Zika merely an innocuous virus that passes inside of a week? Is it a potentially fatal threat to prenatal infants? Or, is it another in a long line of arthropod-borne viruses — some of which could be lethal — that will emerge from ecosystems disturbed by human encroachment? Perhaps only time and an extensive amount of research will tell.