Infectious Diseases A Through Z

Zika Virus

With this new column, Colibri Group will compile an index of various infectious diseases, with occasional highlights of emerging conditions.

Z

Zika Virus Infection

General definition and information:
A mosquito-borne flavivirus, a genus of viruses that also includes the West Nile virus, yellow fever, and other conditions, Zika can trigger a trigger Guillain-Barré syndrome, neuropathy, and myelitis. A member of a family of positive, single-stranded, enveloped RNA viruses that are found in arthropods (primarily ticks and mosquitoes), it was first identified in 1947 among in Ugandan monkeys before being later identified in humans in 1952, according to the World Health Organization (WHO). Symptoms are generally mild and include fever, rash, conjunctivitis, muscle and joint pain, malaise, and/or headache lasting for 2-7 days, and Zika in rarely fatal, according to the Centers for Disease Control and Prevention (CDC), but certain patient populations remain at increased risk for the severe complications that are associated with the virus. These populations include pregnant women (and their fetuses), those women planning or trying to become pregnant, those who are planning to or recently have traveled, and those who have never contracted the virus (contracting the virus provides future immunity). In rare instances, the virus may cause severe disease affecting the brain, causing swelling of the brain or spinal cord, or a blood disorder.

SIDEBAR

Biotech Company Earns Fast Track From FDA for Zika Vaccine

Massachusetts-based biotechnology company Moderna Inc., has reportedly received word from officials with the U.S. Food and Drug Administration (FDA) that the company has granted Fast Track designation for its investigational Zika vaccine. The vaccine (mRNA-1893) is currently being evaluated in a phase 1 study for the prevention of the Zika virus in otherwise healthy adults. Although the FDA had not yet made its decision public as of ADVANCE press time, Moderna officials released the information on Aug. 19. Fast Track is designed to facilitate the development and expedite the review of therapies and vaccines for serious conditions and fill an unmet medical need, officials said in a prepared statement. Programs with Fast Track designation may benefit from early and frequent communication with the FDA, in addition to a rolling submission of the marketing application.

“Protecting against Zika virus transmission, particularly in women during pregnancy, continues to be an area of high unmet need,” said Tal Zaks, MD, PhD, chief medical officer at Moderna, in a prepared statement. “Our Zika program is part of Moderna’s broader commitment to improving global public health through developing mRNA vaccines to prevent the spread of infectious diseases. Fast Track designation supports our belief in the clinical potential of mRNA-1893 and the importance of developing an effective vaccine that can be rapidly developed and deployed.”

The mRNA-1893 contains an mRNA sequence encoding for the structural proteins of Zika virus and is designed to cause cells to secrete virus-like particles, mimicking the response of the cell after natural infection. Preclinical data published in The Journal of Infectious Diseases have shown that vaccination with mRNA-1893 protected against transmission of Zika virus during pregnancy in mice.4

The randomized, observer-blind, placebo-controlled, dose-ranging study is designed to evaluate the safety, tolerability, and immunogenicity of mRNA-1893 in healthy flavivirus seropositive and seronegative adults ages 18-49 years, officials said. Primary outcome measures include frequency and grade of adverse events. Secondary outcome measures include geometric mean titers of neutralizing antibodies against Zika virus.

Causes & Modes of Transmission:

Usually spread through the bite of an infected mosquito (specifically the Aedes species), the virus may also be transmitted during sexual activity with an infected individual, from a mother to her unborn child during pregnancy, and during a transfusion of blood and blood products or an organ transplantation. According to the CDC, the type of mosquitoes known to pass along the virus typically lay eggs in or near standing water, including buckets, bowls, animal dishes, flower pots, and vases. These mosquitoes also prefer to bite humans and will likely live indoors and outdoors near humans.1 Mosquitoes become infected with a virus when they bite an infected person during the period of time when the virus can be found in that person’s blood, typically only through the first week of infection, according to the CDC. Infected mosquitoes can then spread the virus to other people through bites.

The virus has also been found in breast milk, but Zika transmission through breast milk has not been confirmed, the CDC reports. Healthcare providers are urged to encourage mothers to breastfeed, even if they were infected or lived in or traveled to an area with risk of Zika. There have also not been any confirmed blood transfusion transmission cases in the United States reported to the CDC, but there have been multiple reports of possible blood transfusion transmission cases in Brazil. There are reports of laboratory-acquired Zika virus infections, although the route of transmission was not clearly established in all cases, according to the CDC, whose officials also claim that there have been no cases of Zika virus transmission in healthcare settings that have been identified in the U.S. Recommendations are available for healthcare providers to help prevent exposure to Zika virus in healthcare settings.2

Diagnosis can only be confirmed by laboratory tests of blood or other body fluids, may be suspected based on symptoms of persons living in or visiting areas with Zika virus transmission and/or Aedes mosquito vectors according to the WHO.

Treatment Strategies:
There is no dedicated medical treatment for the Zika virus or a vaccine, though a vaccine may soon be a reality (see sidebar). There is no specific medicine or vaccine for Zika virus. The CDC advises healthcare professionals to “treat the symptoms”: encourage patients to get plenty of rest, to drink fluids to prevent dehydration, and to take acetaminophen to reduce fever and pain. (However, patients should not be advised to take aspirin and other NSAIDS until dengue can be ruled out to reduce the risk of bleeding.) If the patient who has been diagnosed with Zika is being looked after by a caregiver, that person (including those who are pregnant) should be educated to take steps to protect themselves from exposure to the patient’s blood and body fluids so that they can safely care for that person. The CDC advises to not touch blood/body fluids or contaminated surfaces, to wash hands with soap and water immediately after providing care, to immediately remove and wash clothes if they get blood or body fluids on them, to clean the sick person’s environment daily using household cleaners, and to immediately clean surfaces that have blood or other body fluids on them.

Prevention Parameters:

Prevention starts with protecting oneself from mosquito exposure through insect repellant, although healthcare providers should also be advocates for safe-sex practices much like they are in relation to sexually transmitted diseases. Helping their patients to be cognizant of at-home mosquito safety and travel destinations that may increases their chances of exposure are also important considerations. Pregnant women should not travel to areas that the CDC has identified to have experienced Zika outbreaks.3 Those who do travel to otherwise safe locations can take additional measures such as staying in places with air conditioning, using window and door screens, sleeping under a mosquito bed net, wearing long pants and shirts whenever possible, and removing an evidence of standing water. Patients who have been diagnosed with Zika may also need appropriate education on how to prevent pregnancy due to the risks to the fetus.

At home, it is important to also follow the aforementioned steps and to eliminate mosquito breeding sites by covering water storage containers, removing standing water in flower pots, and cleaning up trash and used tires.

References

  1. Zika, Mosquitoes, and Standing Water. CDC. 2016. Accessed online: https://blogs.cdc.gov/publichealthmatters/2016/03/zikaandwater
  2. Healthcare Exposure to Zika and Infection Control. CDC. 2017. Accessed online: www.cdc.gov/zika/hc-providers/infection-control.html
  3. Zika Travel Information. CDC. 2019. Accessed online: wwwnc.cdc.gov/travel/page/zika-travel-information
  4. Jagger BW, Dowd KA, Chen RE, et al. Protective efficacy of nucleic acid vaccines against transmission of Zika virus during pregnancy in mice. J Infect Dis. 2019. [Epub ahead of print] https://doi.org/10.1093/infdis/jiz338

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