Doctor's Notes on Zika Virus
Zika virus (Flavivirus) is a viral pathogen that causes Zika fever; the virus is transmitted to humans by mosquito bites or human to human by sexual contact and can be a cause of severe birth defects. Signs and symptoms of Zika fever include fever and chills, joint pain, skin rash and red eyes. The signs and symptoms usually resolve on their own. However, the virus can remain viable for many months in the body. For example, Zika virus can be found in the eyes and the semen for many months even if symptoms have resolved. It can infect the fetus at almost anytime the mother becomes infected during pregnancy, with microcephaly (small head) and other birth defects such as delayed development, intellectual disability and neurological abnormalities as possible outcomes of the infection for the fetus.
The cause of zika fever is infection by the Zika virus. Zika virus is mainly transmitted by mosquito bites in endemic areas (tropical and sub-tropical) but can be transmitted person to person by any sexual activity. Because the virus remains viable in the body even months after symptoms resolve, the infected person may still transmit the Zika viruses by sexual contact to others; over time, however, the risk of infection decreases. Researchers are trying to determine how long people are infective to others.
Zika Virus Symptoms
Most people do not know they are infected with Zika virus. Only 20% of people who are infected develop any symptoms or signs. Zika fever begins with mild headache, followed by a maculopapular rash (pink spots and bumps) starting on the head and upper body and spreading to the palms of the hands and soles of the feet. Very few infections produce a rash on the palms and soles, so this may help identify the infection. Weakness and muscle and joint aches (myalgia and arthralgia) occur, as well as a short period of low-grade fever. Conjunctivitis (red eyes) may occur, as well as stomach pain and diarrhea. These symptoms are usually mild and resolve within a week without specific treatment. Most cases do not require hospitalization. Several of the symptoms of Zika infection are similar to dengue and Chikungunya, which can occur at the same time and may be transmitted by the same mosquitoes in the same areas. In some cases, more serious illness may occur, such as meningoencephalitis. The symptoms of meningoencephalitis are headache, eye sensitivity to light (photophobia), confusion, and inability to bend the neck forward (cannot touch the chin to the chest; stiff neck).
Infants infected in the womb of mothers who were infected with Zika virus at any point in pregnancy may have severe birth defects such as microcephaly (abnormally small head and abnormal brain development), vision and hearing problems, intracranial calcifications, and other physical deformities.
The Zika virus is a Flavivirus related to dengue fever, West Nile virus, yellow fever, and Japanese encephalitis viruses. Zika fever, as it is also known, is transmitted to humans through bites from a mosquito infected with the Zika virus. Common Zika infection symptoms include rash, fever, and joint pain as well as inflammation of the conjunctiva of the eyes, leading to redness. Typically the illness is mild and lasts from a few days to a week. Serious illness is rare, but in February 2016 the World Health Organization declared Zika virus infections as a public-health emergency due to severe birth defects associated with Zika infections during pregnancy.
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Kasper, D.L., et al., eds. Harrison's Principles of Internal Medicine, 19th Ed. United States: McGraw-Hill Education, 2015.