Zika - A Mosquito Borne Viral Disease
A Topic For Curious Patients
The Zika virus is a mosquito borne viral disease. No other animal infects and causes disease as effectively as mosquitos, which are the deadliest animals in the world to humans. Infections caused by mosquitos kill over 700,000 people a year.
This is part 1 of a four part series on mosquito borne viral diseases. In this article we will look at Zika. The future articles will cover Dengue, chikungunya, and West Nile. Currently West Nile is endemic in the continental US, but clinicians may see the other three diseases in travelers who are either from, or who have visited endemic areas. It is also possible that like Zika a few years ago, these diseases may become endemic in the U.S. at some time in the future. The following is Part 1- Zika.
In 2015 and 2016 Zika was a front-page news story due to surging infections in the Americas, with the threat of severe fetal brain defects occurring if pregnant women were infected. Since then, Zika has almost disappeared. In 2016, there were 5,168 reported cases in the U.S. and 36,512 cases in U.S. territories, with widespread transmission in Puerto Rico and the U.S. Virgin Islands, and limited local transmission in Florida and Texas. Brazil had 200,000 reported Zika cases in 2016, and infants born with microcephaly increased 10-fold from prior levels in late 2015 to early 2016. By 2019, there were only 27 reported U.S. cases in travelers and 74 cases in U.S. territories. There are currently no countries with a large outbreak of Zika. Some experts do not think pesticide spraying has caused the decline, and it is possible that a form of herd immunity in endemic areas has occurred, limiting the ability of mosquitos to spread Zika to humans.
Zika virus is an RNA Flavivirus transmitted by Aedes aegypti and Aedes albopictus mosquitos. Human to human transmission also occurs, and potentially it can be transmitted by blood transfusion and sexual contact. Zika virus was first discovered in 1947 and is named after the Zika Forest in Uganda. The first human case was reported in 1952.
Zika Clinical Disease
Most people infected with Zika virus are asymptomatic. Clinical findings typically are acute onset of fever with rash, arthralgia (joint aches), and/or conjunctivitis (pinkeye). Myalgias (muscle aches) and headaches are common. The illness is usually mild with symptoms lasting from several days to a week. Severe disease requiring hospitalization is uncommon, and fatalities are rare. There have been some cases of Guillain-Barré syndrome (an autoimmune disease that can cause numbness, weakness and potentially paralysis starting in the legs and moving up the body) reported after a Zika infection. Zika virus infection during pregnancy can cause fetal microcephaly (smaller than expected head size), decreased brain tissue, and damage to the back of the eyes.
No specific treatment is available for Zika virus disease, other than supportive care. As dengue presents similarly, and in the same geographic areas as Zika, aspirin and other non-steroidal anti-inflammatory drugs (NSAIDs), such as ibuprofen should be avoided until dengue can be ruled out, to reduce the risk of hemorrhage. People infected with Zika, should be protected from mosquito exposure during the first few days of illness to reduce the risk of further human to mosquito to human transmission. Sexual relations should be curtailed to prevent passing on the infection.
A vaccine has been developed, but gaining approval by testing it in an environment of decreasing cases has proved difficult.
Sexual Transmission 
Zika can be sexually transmitted by sharing sex toys, and by vaginal, anal, and possibly oral sex, even if asymptomatic. Zika virus has been detected in semen, vaginal fluids, saliva, urine, and breast milk. There is no evidence however, that Zika can be transmitted through saliva during kissing. Zika virus has been reported to persist in semen for up to 69 days. It is recommended that pregnant women with sexual partners who live in, or have traveled to, an endemic Zika area, use condoms during sex, or abstain from sexual relations for the duration of the pregnancy. Condom use is recommended after travelling to an endemic area for two months for nonpregnant females, and three months for males, due to the longer survival time in semen.
Zika testing of symptomatic male and female non-pregnant patients is not currently recommended by the CDC based on current epidemiology, but this guidance may change in the case of a renewed outbreak of cases. However, these patients should be tested for dengue virus, which is more common, and has similar presenting features. Testing asymptomatic males and non-pregnant females for either dengue or Zika viruses is not currently recommended.
Zika testing involves a very complex algorithm for pregnant women. Recommended testing is different if the woman is symptomatic, asymptomatic, has had an abnormal fetal ultrasound consistent with a congenital Zika infection, or has had sexual relations with someone suspected of having the disease. If you are interested in learning more about the complete CDC Zika testing guidelines algorithm for pregnant women, follow this link: https://www.cdc.gov/zika/hc-providers/testing-guidance.html
Eastern equine encephalitis
La Crosse encephalitis
Rift Valley fever
Ross River virus disease
St. Louis encephalitis
Dirofilariasis (dog heartworm)
 Nuwer R. Mosquitoes Kill More Humans Than Human Murderers Do. SMITHSONIANMAG.COM. April 30, 2014. Retrieved from: https://www.smithsonianmag.com/smart-news/mosquitoes-kill-more-humans-human-murderers-do-180951272/
 Cohen J. Zika has all but disappeared in the Americas. Why? Science. Aug. 16, 2017. Retrieved from: https://www.sciencemag.org/news/2017/08/zika-has-all-disappeared-americas-why
 Zika, 2016 Case Counts in the US. CDC. Last reviewed: April 24, 2019. Retrieved from: https://www.cdc.gov/zika/reporting/2016-case-counts.html
 Lowe R et al. The Zika Virus Epidemic in Brazil: From Discovery to Future Implications. Int J Environ Res Public Health. 2018;15(1):96. Published Jan 9, 2018. Retrieved from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5800195/#B18-ijerph-15-00096
 Zika Virus, 2019 Case Counts in the US. CDC. Last reviewed: December 2, 2020. Retrieved from https://www.cdc.gov/zika/reporting/2019-case-counts.html
 Zika Virus, History of Zika. CDC. Last reviewed: October 7, 2019. Retrieved from: https://www.cdc.gov/zika/about/overview.html
 Zika Virus, Clinical Evaluation & Disease. CDC. Last reviewed: January 28, 2019. Retrieved from: https://www.cdc.gov/zika/hc-providers/preparing-for-zika/clinicalevaluationdisease.html
 Zika Virus, Microcephaly & Other Birth Defects. CDC. Last reviewed: May 14, 2019. Retrieved from: https://www.cdc.gov/zika/healtheffects/birth_defects.html
 Pictures by Jose Antonio Suarez in Rodriguez-Morales A et al. Introductory Chapter: Clinical and Epidemiological Implications of Zika Virus Infection -The Experience of RECOLZIKA in Colombia. Intechopen. 2018. Retrieved from: https://www.researchgate.net/publication/325754352_Introductory_Chapter_Clinical_and_Epidemiological_Implications_of_Zika_Virus_Infection_-The_Experience_of_RECOLZIKA_in_Colombia/download
 Zika Virus, Clinical Guidance for Healthcare Providers for Prevention of Sexual Transmission of Zika Virus. CDC. Last reviewed: January 28, 2019. https://www.cdc.gov/zika/hc-providers/clinical-guidance/sexualtransmission.html
 NEW Zika and Dengue Testing Guidance. CDC. Updated November 2019. Retrieved from: https://www.cdc.gov/zika/hc-providers/testing-guidance.html
Initial publication 12/16/2021