Zika virus infection overview
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Nate Michalak, B.A.
Overview
Zika fever is an infectious disease caused by the Zika virus (ZIKV), an enveloped, single stranded positive sense RNA Flavivirus. Zika virus is a vector-borne pathogen usually transmitted via the Aedes mosquito that also transmits the dengue and chikungunya viruses. Human-to-human transmission may be possible by sexual intercourse but has not been confirmed. Once rare, the incidence of Zika virus infection is thought to have risen dramatically, particularly in Brazil as observed by the manifestation of a correlated complication, microcephaly, in infants born to mothers with Zika virus infection. Zika virus infection's broad ranging clinical symptoms cause it to be commonly misdiagnosed with multiple similar diseases that are also from the Flaviviridae virus family. Zika virus infection has similar clinical presentation to Dengue fever, yellow fever, West Nile virus, and Japanese encephalitis. Zika virus infection is distinct in its milder clinical manifestations and short length of infection. Patients exposed to Zika virus will develop symptoms 3 and 12 days after contracting the disease. Symptoms will typically begin with a mild headache and progress to include a maculopapular rash spread across the body within 24 hours, followed by fever, malaise, and back pain. The symptoms typically last 4-7 days. The prognosis is excellent, with the majority of patients recovering fully. Complications include congenital and neurological sequelae, particularly Guillain-Barré syndrome and microcephaly. Diagnosis is usually made by either ELISA and PCR. Treatment is usually supportive, and antiviral therapy is generally not recommended. There are no vaccines available to prevent Zika virus infection. Since the virus is usually transmitted through mosquitoes, effective measures to avoid mosquito bites include using insect repellent, installing mosquito bed nets and window/door screens, wearing long sleeves and long pants, and removing potential breeding sites from indoor/outdoor premises. Once infected, individuals may be re-infected in the future.
Historical Perspective
Zika virus was first isolated from a rhesus Monkey in 1947 in Uganda. The virus was first isolated from humans in 1968 in Nigeria. Since then, viral circulation and outbreaks have been documented throughout Asia and Africa. The most recent outbreak occurred in Brazil in April 2015.
Pathophysiology
Zika virus is a vector-borne pathogen usually transmitted via the Aedes mosquito that also transmits the dengue and chikungunya viruses. Human-to-human transmission may be possible by sexual intercourse but has not been confirmed. Zika virus is thought to initially replicate in dendritic cells near the site of inoculation before spreading to lymph nodes and then the bloodstream. Guillain-Barré syndrome and congenital microcephaly have been loosely associated with Zika virus disease. The most potent risk factor in the development of Zika virus infection is travel to endemic areas. Other risk factors include exposure to infected individuals via blood transfusion, sexual intercourse, or vertically to fetuses from infected mothers.
Causes
Zika virus infection is cause by Zika virus, an enveloped, single stranded positive sense RNA virus. Zika virus is a type of flavivirus and is primarily transmitted through mosquitoes.
Classification
A schema for the classification of Zika virus infection is yet to be developed.
Differential Diagnosis
Zika virus infection's broad ranging clinical symptoms cause it to be commonly misdiagnosed with multiple similar diseases that are also from the Flaviviridae virus family. Zika virus infection has similar clinical presentation to Dengue fever, yellow fever, West Nile virus, and Japanese encephalitis. Zika virus infection is distinct in its milder clinical manifestations and short length of infection. The association between Zika virus infection and complications that include congenital anomalies and neurological syndromes is also distinctive. Of note, patients bitten by mosquitoes may be concomitantly infected with Zika virus and other mosquito-borne infections, and co-infection should always be considered.
Epidemiology and Demographics
In 2015, Zika virus infection outbreaks rose dramatically, particularly in Brazil as observed by the manifestation of a correlated complication, microcephaly, in infants born to mothers with Zika virus infection, an incidence of approximately 100 per 100,000 infants. The majority of Zika virus infection cases are reported in South Africa and Tropical Asia. As of 2014, Zika Virus infection outbreaks have also become more common in South America. Cases reported in other regions of the world are attributed to travel from areas with outbreaks. Zika virus infection affects all age groups, with newborn infants particularly vulnerable due to risk of transmission from the mothers upon birth.
Risk Factors
The most potent risk factor in the development of Zika virus infection is travel to endemic areas. Other risk factors include exposure to infected individuals via blood transfusion, sexual intercourse, or vertically to fetuses from infected mothers.
Natural History, Complications & Prognosis
Patients exposed to Zika virus will develop symptoms 3 and 12 days after contracting the disease. Symptoms will typically begin with a mild headache and progress to include a maculopapular rash spread across the body within 24 hours, followed by fever, malaise, and back pain. The symptoms typically last 4-7 days. The prognosis is excellent, with the majority of patients recovering fully. Complications include congenital and neurological sequelae, particularly Guillain-Barré syndrome and microcephaly.
Diagnosis
History and Symptoms
The most common symptoms of Zika virus include fever and maculopapular rash. Additional symptoms include arthralgia, conjunctivitis, myalgia, headache, retro-orbital pain, and vomiting.
Physical Examination
Physical examination of patients with Zika virus infection is usually remarkable for fever and a maculopapular rash that often includes the face, trunk, and extremities (may include the palms and soles). Other physical examination findings include non-purulent conjunctivitis and edema.
Laboratory Findings
The diagnosis of Zika virus infection is usually made by detection of elevated IgM and IgG Zika virus antibodies by ELISA or viral RNA by RT-PCR. Non-specific lab findings include elevated markers of inflammation, mild neutropenia, normal leukocyte count or mild leukocytosis with normal platelet count and liver function tests.
Evaluation of Pregnant Women
According to the CDC, pregnant women suspected to have Zika virus infection may be required to undergo amniocentesis and testing of histopathologic samples of the placenta and umbilical cord, frozen placental tissue and cord tissue for Zika virus RNA, and cord serum for Zika and dengue virus IgM and neutralizing antibodies.
Evaluation of Infants
According to the CDC, zika virus testing is recommended among 1) infants with microcephaly or intracranial calcifications born to women who traveled to or resided in an area with Zika virus transmission while pregnant, or 2) infants born to mothers with positive or inconclusive test results for Zika virus infection. When an infant is born with microcephaly or intracranial calcifications to a mother who was potentially infected with Zika virus during pregnancy, the infant should be tested for Zika virus infection and ophthalmologic examination. For an infant without microcephaly or intracranial calcifications born to a mother who was potentially infected with Zika virus during pregnancy, subsequent evaluation is dependent on results from maternal Zika virus testing. Developmental monitoring and screening during the first year of life is recommended for all children with congenital Zika virus infection.
Other Diagnostic Studies
There are no other diagnostic studies associated with Zika virus infection.
Treatment
Medical Therapy
The mainstay of therapy for Zika virus infection is supportive care. Supportive care includes includes rest, adequate fluids intake, and administration of antipyretics and analgesics. Aspirin and other NSAIDs should be avoided until Dengue fever is ruled out (NSAIDs may increase the risk of hemorrhage in Dengue fever). Antiviral treatment is not recommended for the management of Zika virus infection. The general principles of medical therapy for the management of Zika virus apply to pregnant women. Treatment of congenital Zika virus infection is supportive and should address specific medical and neurodevelopmental issues for the infant’s particular needs. Mothers are encouraged to breastfeed infants even in areas where Zika virus is found, as available evidence indicates the benefits of breastfeeding outweigh any theoretical risks associated with Zika virus infection transmission through breast milk.[1][2]
Surgery
Surgery is not recommended for the management of Zika virus infection.
Prevention
There are no vaccines available to prevent Zika virus infection. Since the virus is usually transmitted through mosquitoes, effective measures to avoid mosquito bites include using insect repellent, installing mosquito bed nets and window/door screens, wearing long sleeves and long pants, and removing potential breeding sites from indoor/outdoor premises. Once infected, individuals may be re-infected in the future.
Travel Notice
The CDC has issued level 2 alert (practice enhanced precautions) for travelers to Cape Verde, the Carribean, Central America, Mexico, Samoa, and South America.
References
- ↑ Besnard M, Lastere S, Teissier A, Cao-Lormeau V, Musso D (2014). "Evidence of perinatal transmission of Zika virus, French Polynesia, December 2013 and February 2014". Euro Surveill. 19 (13). PMID 24721538.
- ↑ Gartner LM, Morton J, Lawrence RA, Naylor AJ, O'Hare D, Schanler RJ; et al. (2005). "Breastfeeding and the use of human milk". Pediatrics. 115 (2): 496–506. doi:10.1542/peds.2004-2491. PMID 15687461.