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Where is Zika Now?

By Aleks Recupero

With all eyes on Brazil for the 2016 Rio Summer Olympics, the growing Zika epidemic made headline after headline. The influx of 11,237 athletes from around the globe in addition to the hundreds of thousands of spectators provided a large vat of susceptible victims for the spreading virus.1 The mounting concern around the Olympic games was not unwarranted. The Summer Olympics have come and gone, but the Zika virus still remains a present threat not only in Brazil but also throughout Central and South America, even extending up into the southern United States. So where is Zika now?

Despite Zika’s present prominence, the virus was actually first seen in Uganda in 1947. For most of the disease’s history, human infections only gave rise to mild sickness with symptoms including fever, skin rashes, conjunctivitis, muscle and joint pain, malaise, and headache.2 Only in 2015 did Brazil observe the relationships between Zika and Guillain-Barré syndrome and Zika and microcephaly.2 With greater understanding of the impacts of the disease, news of Zika spread, along with the virus’s vector.

Mosquitos of the Aedes genus have been found to be the main means of transmission of the Zika virus. In this way, the best present precaution is to protect against mosquito bites. The mosquitos capable of spreading Zika inhabit much of the United States, but infections in the US have remained under control and contained to small areas.3

 

As of March 10th, 2017, sixty-one countries have had new introduction or re-introduction of Zika with ongoing transmission. Eighteen countries had Zika circulation prior to 2015 or have ongoing transmission. Five countries have had interrupted transmission but maintain the potential for future transmission. Sixty-four countries have the competent Aedes mosquito vector but have not had previous or current transmission of the virus;4 obviously Zika is still very prevalent despite the lull in press following the Rio Games. Even more astounding, there are no FDA-approved treatments, vaccines, or even a diagnostic test for Zika.5

 

It would be remiss to say that experimental diagnostic tests do not exist. In fact, the Aptima Zika Virus assay received Emergency Use Authorization from the FDA on June 17th, 2016 for detection of the RNA of the Zika virus in human blood and urine. In a clinical trial, this diagnostic test produced a 94.8% diagnostic accuracy. In addition, the Aptima Zika Virus assay was found to be one hundred fold more sensitive than the other leading emergency diagnostic tool, the Trioplex Real-time RT-PCR assay.6 Zika diagnosis is also complicated by the fact that serological analysis often leads to misdiagnosis of dengue virus due to their antigenic similarity.7,8 Such an obstacle is made evident by the FDA’s hesitation to fully clear a diagnostic test. Further research and clinical trails continue to seek better and more accurate diagnostic measures for Zika virus.

 

A vaccine remains high on the World Health Organization’s agenda for combatting Zika. Vaccines reduce the number of susceptible individuals to a particular disease by providing people with immunity. In this way, vaccines reduce the force of an infection while increasing the average age of infection. The basic reproductive number (R0) of a disease depends on the disease’s transmission rate, the number of susceptible individuals in the population, and the duration of the disease. Vaccines can reduce the R0 of a disease by reducing the number of susceptibles in the population. In contrast, reducing vectors has little effect on the basic reproductive number of a disease, leaving vaccines as a useful means to combat Zika.

 

The National Institute of Allergy and Infectious Diseases has found many vaccine candidates for Zika virus. A DNA-based vaccine has undergone a Phase 1 clinical trial and has been determined to be safe and capable of counteracting an antibody response to Zika. In March 2017, a Phase 2 clinical trail was launched in areas with the potential for Zika transmission. The purpose of this trial is to determine the proper dose of the vaccine while also ensuring prevention of the disease following Zika infection. A live-attenuated vaccine supposed to protect against both Zika and dengue virus is in a Phase 3 study within Brazil. A purified inactivated vaccine, mRNA vaccines, a genetically engineered vaccine, and a multiple mosquito-borne disease vaccine are all also in trials.9 

 

Despite the pouring of resources into discovering a vaccine for Zika, the best means to combat Zika is still not known. In children or non-pregnant adults, the immune system fights the Zika virus with symptoms including a mild fever, muscle and joint pain, malaise, and headache ranging from two to seven days.2 With improper treatment, Guillain-Barré syndrome, a potentially life-threatening autoimmune disorder that attacks the peripheral nervous system, can result.10 Therefore, the spread of Zika virus in impoverished areas puts many at risk for Guillain-Barré syndrome due to the lack of proper treatment for Zika infection. For the most part Zika infection is mild and recovery is expected. However, for pregnant women, Zika infection causes infant brain abnormalities such as microcephaly. Therefore, in the prevention of the disease, the most at risk are pregnant women. Childhood Zika infection is believed to be able to produce an immune adult population. In contrast, childhood vaccination, with loss of immunity over time and the increased age of first infection, could produce a susceptible adult population. Whether or not childhood infection is most beneficial for the ultimate immunity and protection of pregnant women is still to be seen. At this time, with the epidemic and the disease spread through poverty-stricken regions, the vaccination is a hopeful solution for the present.

Despite the passing of the Rio Olympics, Zika virus remains a very present threat throughout the Americas. New diagnostic methods and a vaccination are atop the lists of many world health organizations. The best means to combat this epidemic will only be seen in time, but the plethora of resources devoted to eradicating Zika provide hope for the virus’s demise.

    

References

  1. International Olympic Committee. 2017. “Rio 2016 Olympics.” Accessed May 7. https://www.olympic.org/rio-2016
  2. World Health Organization. 2016. “Zika virus.” Accessed May 7. http://www.who.int/mediacentre/factsheets/zika/en/
  3. Centers for Disease Control and Prevention. 2016. “Zika Virus: Potential Range in US.” Accessed May 7. https://www.cdc.gov/zika/vector/range.html
  4. World Health Oranization. 2017. “Zika situation report.” Accessed May 7. http://www.who.int/emergencies/zika-virus/situation-report/10-march-2017/en/
  5. U.S. Food and Drug Administration. 2017. “Zika Virus Response Updates from FDA.” Accessed May 7. https://www.fda.gov/EmergencyPreparedness/Counterterrorism/MedicalCountermeasures/MCMIssues/ucm485199.htm#bydate
  6. Ren, Ping et al. 2017. “Evaluation of Aptima Zika Virus Assay.” Journal of Clinical Microbiology 55, 5. 
  7. Liang, Dachao et al. 2017. “Insights into intercontinental spread of Zika virus.” PLoS ONE 12(4). 
  8. Dejnirattisai, Wanwisa et al. 2016. “Dengue virus sero-cross-reactivity drives antibody-dependent enhancement of infection with zika virus.” Nature Immunology 17, 1102-1108. 
  9. National Institute of Allergy and Infectious Diseases. 2017. “Zika Virus.” Accessed May 7. https://www.niaid.nih.gov/diseases-conditions/zika-vaccines
  10. World Health Organization. 2016. “Guillain-Barré syndrome.” Accessed May 18. http://www.who.int/mediacentre/factsheets/guillain-barre-syndrome/en/

 

Image Credit (Creative Commons): “CDC Zika active transmission map Sept 2016.” Accessed May 18, 2017. https://commons.wikimedia.org/wiki/File:CDC_Zika_active_transmission_map_Sept_2016.jpg

 

Aleksandra Recupero is a first-year student at the University of Chicago majoring in Biological Sciences. Her interests include medicine and neuroscience research.

 

With all eyes on Brazil for the 2016 Rio Summer Olympics, the growing Zika epidemic made headline after headline. The influx of 11,237 athletes from around the globe in addition to the hundreds of thousands of spectators provided a large vat of susceptible victims for the spreading virus.1 The mounting concern around the Olympic games was not unwarranted. The Summer Olympics have come and gone, but the Zika virus still remains a present threat not only in Brazil but also throughout Central and South America, even extending up into the southern United States. So where is Zika now?

Despite Zika’s present prominence, the virus was actually first seen in Uganda in 1947. For most of the disease’s history, human infections only gave rise to mild sickness with symptoms including fever, skin rashes, conjunctivitis, muscle and joint pain, malaise, and headache.2 Only in 2015 did Brazil observe the relationships between Zika and Guillain-Barré syndrome and Zika and microcephaly.2 With greater understanding of the impacts of the disease, news of Zika spread, along with the virus’s vector.

Mosquitos of the Aedes genus have been found to be the main means of transmission of the Zika virus. In this way, the best present precaution is to protect against mosquito bites. The mosquitos capable of spreading Zika inhabit much of the United States, but infections in the US have remained under control and contained to small areas.3

As of March 10th, 2017, sixty-one countries have had new introduction or re-introduction of Zika with ongoing transmission. Eighteen countries had Zika circulation prior to 2015 or have ongoing transmission. Five countries have had interrupted transmission but maintain the potential for future transmission. Sixty-four countries have the competent Aedes mosquito vector but have not had previous or current transmission of the virus;4 obviously Zika is still very prevalent despite the lull in press following the Rio Games. Even more astounding, there are no FDA-approved treatments, vaccines, or even a diagnostic test for Zika.5

It would be remiss to say that experimental diagnostic tests do not exist. In fact, the Aptima Zika Virus assay received Emergency Use Authorization from the FDA on June 17th, 2016 for detection of the RNA of the Zika virus in human blood and urine. In a clinical trial, this diagnostic test produced a 94.8% diagnostic accuracy. In addition, the Aptima Zika Virus assay was found to be one hundred fold more sensitive than the other leading emergency diagnostic tool, the Trioplex Real-time RT-PCR assay.6 Zika diagnosis is also complicated by the fact that serological analysis often leads to misdiagnosis of dengue virus due to their antigenic similarity.7,8 Such an obstacle is made evident by the FDA’s hesitation to fully clear a diagnostic test. Further research and clinical trails continue to seek better and more accurate diagnostic measures for Zika virus.

A vaccine remains high on the World Health Organization’s agenda for combatting Zika. Vaccines reduce the number of susceptible individuals to a particular disease by providing people with immunity. In this way, vaccines reduce the force of an infection while increasing the average age of infection. The basic reproductive number (R0) of a disease depends on the disease’s transmission rate, the number of susceptible individuals in the population, and the duration of the disease. Vaccines can reduce the R0 of a disease by reducing the number of susceptibles in the population. In contrast, reducing vectors has little effect on the basic reproductive number of a disease, leaving vaccines as a useful means to combat Zika.

The National Institute of Allergy and Infectious Diseases has found many vaccine candidates for Zika virus. A DNA-based vaccine has undergone a Phase 1 clinical trial and has been determined to be safe and capable of counteracting an antibody response to Zika. In March 2017, a Phase 2 clinical trail was launched in areas with the potential for Zika transmission. The purpose of this trial is to determine the proper dose of the vaccine while also ensuring prevention of the disease following Zika infection. A live-attenuated vaccine supposed to protect against both Zika and dengue virus is in a Phase 3 study within Brazil. A purified inactivated vaccine, mRNA vaccines, a genetically engineered vaccine, and a multiple mosquito-borne disease vaccine are all also in trials.9 

Despite the pouring of resources into discovering a vaccine for Zika, the best means to combat Zika is still not known. In children or non-pregnant adults, the immune system fights the Zika virus with symptoms including a mild fever, muscle and joint pain, malaise, and headache ranging from two to seven days.2 With improper treatment, Guillain-Barré syndrome, a potentially life-threatening autoimmune disorder that attacks the peripheral nervous system, can result.10 Therefore, the spread of Zika virus in impoverished areas puts many at risk for Guillain-Barré syndrome due to the lack of proper treatment for Zika infection. For the most part Zika infection is mild and recovery is expected. However, for pregnant women, Zika infection causes infant brain abnormalities such as microcephaly. Therefore, in the prevention of the disease, the most at risk are pregnant women. Childhood Zika infection is believed to be able to produce an immune adult population. In contrast, childhood vaccination, with loss of immunity over time and the increased age of first infection, could produce a susceptible adult population. Whether or not childhood infection is most beneficial for the ultimate immunity and protection of pregnant women is still to be seen. At this time, with the epidemic and the disease spread through poverty-stricken regions, the vaccination is a hopeful solution for the present.

Despite the passing of the Rio Olympics, Zika virus remains a very present threat throughout the Americas. New diagnostic methods and a vaccination are atop the lists of many world health organizations. The best means to combat this epidemic will only be seen in time, but the plethora of resources devoted to eradicating Zika provide hope for the virus’s demise.

References

  1. International Olympic Committee. 2017. “Rio 2016 Olympics.” Accessed May 7. https://www.olympic.org/rio-2016
  2. World Health Organization. 2016. “Zika virus.” Accessed May 7. http://www.who.int/mediacentre/factsheets/zika/en/
  3. Centers for Disease Control and Prevention. 2016. “Zika Virus: Potential Range in US.” Accessed May 7. https://www.cdc.gov/zika/vector/range.html
  4. World Health Oranization. 2017. “Zika situation report.” Accessed May 7. http://www.who.int/emergencies/zika-virus/situation-report/10-march-2017/en/
  5. U.S. Food and Drug Administration. 2017. “Zika Virus Response Updates from FDA.” Accessed May 7. https://www.fda.gov/EmergencyPreparedness/Counterterrorism/MedicalCountermeasures/MCMIssues/ucm485199.htm#bydate
  6. Ren, Ping et al. 2017. “Evaluation of Aptima Zika Virus Assay.” Journal of Clinical Microbiology 55, 5. 
  7. Liang, Dachao et al. 2017. “Insights into intercontinental spread of Zika virus.” PLoS ONE 12(4). 
  8. Dejnirattisai, Wanwisa et al. 2016. “Dengue virus sero-cross-reactivity drives antibody-dependent enhancement of infection with zika virus.” Nature Immunology 17, 1102-1108. 
  9. National Institute of Allergy and Infectious Diseases. 2017. “Zika Virus.” Accessed May 7. https://www.niaid.nih.gov/diseases-conditions/zika-vaccines
  10. World Health Organization. 2016. “Guillain-Barré syndrome.” Accessed May 18. http://www.who.int/mediacentre/factsheets/guillain-barre-syndrome/en/

Image Credit (Creative Commons): “CDC Zika active transmission map Sept 2016.” Accessed May 18, 2017. https://commons.wikimedia.org/wiki/File:CDC_Zika_active_transmission_map_Sept_2016.jpg

Aleksandra Recupero is a first-year student at the University of Chicago majoring in Biological Sciences. Her interests include medicine and neuroscience research.

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