- Zika Virus By Jaikumar pareta
- Introduction :
- Zika virus is transmitted to humans by infected mosquitoes. It causes mild fever and rash. Other symptoms include muscle pain, joint pain, headache, pain behind the eyes and conjunctivitis.
- Zika virus disease is usually mild, with symptoms lasting only a few days.
- The disease has similar clinical signs to dengue, and may be misdiagnosed in areas where dengue is common.
- There is no cure for Zika virus disease. Treatment is focused on relieving the symptoms.
- Prevention and control relies on reducing the breeding of Aedes mosquitoes and minimizing contact between mosquito vectors and people by using barriers (such as repellents, insect screens), reducing water-filled habitats supporting mosquito larvae in and close to dwellings, and reducing the adult mosquito populations around at-risk communities.
Background
Zika virus is a mosquito-borne flavivirus closely related to dengue virus. It was first isolated from a rhesus monkey in Zika forest, Uganda in 1947, in mosquitoes (Aedes africanus) in the same forest in 1948 and in humans in Nigeria in 1954. Zika virus is endemic in parts of Africa and Asia and was first identified in the South Pacific after an outbreak on Yap Island in the Federated States of Micronesia in 2007.
Transmission
Zika virus is primarily transmitted to humans through bites from Aedes mosquitos, which often live around buildings in urban areas and are usually active during daylight hours (peak biting activity occurs in early mornings and late afternoons).
Some evidence suggests Zika virus can also be transmitted to humans through blood transfusion, perinatal transmission and sexual transmission. However, these modes are very rare.
The incubation period is typically between 2 and 7 days.
Signs and symptoms
Zika virus infection is characterized by low grade fever (less than 38.5°C) frequently accompanied by a maculopapular rash. Other common symptoms include muscle pain, joint pain with possible swelling (notably of the small joints of the hands and feet), headache, pain behind the eyes and conjunctivitis. As symptoms are often mild, infection may go unrecognized or be misdiagnosed as dengue.
A high rate of asymptomatic infection with Zika virus is expected, similar to other flaviviruses, such as dengue virus and West Nile virus. Most people fully recover without severe complications, and hospitalization rates are low. To date, there have been no reported deaths associated with Zika virus.
Diagnosis
Several methods can be used for diagnosis, such as viral nucleic acid detection, virus isolation and serological testing. Nucleic acid detection by reverse transcriptase-polymerase chain reaction targeting the non-structural protein 5 genomic region is the primary means of diagnosis, while virus isolation is largely for research purposes. Saliva or urine samples collected during the first 3 to 5 days after symptom onset, or serum collected in the first 1 to 3 days, are suitable for detection of Zika virus by these methods. Serological tests, including immunofluorescence assays and enzyme-linked immunosorbent assays may indicate the presence of anti-Zika virus IgM and IgG antibodies. Caution should be taken with serological results as IgM cross reactivity with other flaviviruses has been reported in both primary infected patients and those with a probable history of prior flavivirus infection.
Treatment
There is no commercial vaccine or specific antiviral drug treatment for Zika virus infection. Treatment is directed primarily at relieving symptoms using anti-pyretics and analgesics.
Prevention and control
The proximity of mosquito vector breeding sites to human habitation is a significant risk factor for Zika virus infection. Prevention and control relies on reducing the breeding of mosquitoes through source reduction (removal and modification of breeding sites) and reducing contact between mosquitoes and people. This can be achieved by reducing the number of natural and artificial water-filled habitats that support mosquito larvae, reducing the adult mosquito populations around at-risk communities and by using barriers such as repellants, insect screens, closed doors and windows, and long clothing. Since the Aedes mosquitoes are day-biting mosquitoes, it is recommended that those who sleep during the daytime, particularly young children, the sick or elderly, should use insecticide-treated mosquito nets to provide protection. Mosquito coils or other insecticide vaporizers may also reduce the likelihood of being bitten.
During outbreaks, space spraying of insecticides may be carried out periodically to kill flying mosquitoes. Suitable insecticides (recommended by the WHO Pesticide Evaluation Scheme) may also be used as larvicides to treat relatively large water containers.
Basic precautions for protection from mosquito bites should be taken by people traveling to high risk areas. These include use of repellents, wearing light colored, long sleeved shirts and pants and ensuring rooms are fitted with screens to prevent mosquitoes from entering.
Disease outbreaks
The first documented outbreak of Zika virus in the South Pacific occurred on Yap Island in the Federated States of Micronesia in 2007. This outbreak affected 180 (confirmed, probable and suspected) people and was characterized by rash, conjunctivitis and joint pain.
In October 2013, French Polynesia reported its first outbreak, which was estimated to affect around 11% of the population. This particular outbreak spread to other Pacific Islands including New Caledonia, Cook Islands, and Easter Island. As most cases of Zika virus infection present with mild illness similar to other circulating arbovirus infections, and there was limited laboratory capacity during this outbreak for the detection of Zika virus, it is likely that many cases of infection were not identified.
More about disease vectors
Both Ae. aegypti and Ae. albopictus have been implicated in large outbreaks of Zika virus. Ae. aegypti is confined to tropical and sub-tropical regions, while Ae. albopictus can be found in tropical, sub-tropical and temperate regions. Ae. albopictus has spread from Asia and become established in areas of the South Pacific, Africa, Europe and the Americas in recent decades. In the South Pacific,Ae. hensilli was implicated in the spread of Zika virus on Yap Island in 2007, while Ae. polynesiensis was suspected to spread Zika virus in French Polynesia in 2013. Neither of these endemic species had been recognized as a Zika virus vector before, indicating that as this emerging disease spreads to previously unaffected countries, the potential exists for other endemic Aedes species to play a role in transmission.
- Ae. aegypti is closely associated with human environments and can breed in indoor (flower vases, concrete water tanks in bathrooms), and artificial outdoor (vehicle tyres, water storage vessels, discarded containers) environments.
- Ae. albopictus thrives in a wider range of water-filled breeding sites than Ae. aegypti, including coconut husks, cocoa pods, bamboo stumps, tree holes and rock pools, in addition to artificial containers such as vehicle tyres and plant pot saucers. This diversity of habitats explains the abundance of Ae. albopictus in rural as well as peri-urban areas and shady city parks.
- Ae. hensilli breeds in coconut shells, tins, plastic containers, vehicle tyres, tree holes, canoes and metal drums.
- Ae. polynesiensis breeds in tree holes, coconut shells and crab holes.
WHO responds to Zika virus infection by:
- Providing technical support and guidance to countries for the effective management of cases and outbreaks;
- Supporting countries to improve their surveillance systems;
- Providing training on clinical management, diagnosis and vector control including through a number of WHO Collaborating Centres;
- Publishing guidelines for vector control; and
- Encouraging countries to develop and maintain the capacity to detect and confirm cases, manage patients, and implement social communication strategies to reduce the presence of the mosquito vectors.
WHO Director-General, Margaret Chan, will convene an International Health Regulations Emergency Committee on Zika virus and observed increase in neurological disorders and neonatal malformations.
The Committee will meet on Monday 1 February in Geneva to ascertain whether the outbreak constitutes a Public Health Emergency of International Concern.
Decisions concerning the Committee’s membership and advice will be made public on WHO’s website.
Outbreak in the Americas
In May 2015, Brazil reported its first case of Zika virus disease. Since then, the disease has spread within Brazil and to 22 other countries and territories in the region.
Arrival of the virus in some countries of the Americas, notably Brazil, has been associated with a steep increase in the birth of babies with abnormally small heads and in cases of Guillain-Barré syndrome, a poorly understood condition in which the immune system attacks the nervous system, sometimes resulting in paralysis.
A causal relationship between Zika virus infection and birth defects and neurological syndromes has not been established, but is strongly suspected.
WHO action
WHO’s Regional Office for the Americas (PAHO) has been working closely with affected countries since May 2015. PAHO has mobilized staff and members of the Global Outbreak and Response Network (GOARN) to assist ministries of health in strengthening their abilities to detect the arrival and circulation of Zika virus through laboratory testing and rapid reporting. The aim has been to ensure accurate clinical diagnosis and treatment for patients, to track the spread of the virus and the mosquito that carries it, and to promote prevention, especially through mosquito control.
The Organization is supporting the scaling up and strengthening of surveillance systems in countries that have reported cases of Zika and of microcephaly and other neurological conditions that may be associated with the virus. Surveillance is also being heightened in countries to which the virus may spread. In the coming weeks, the Organization will convene experts to address critical gaps in scientific knowledge about the virus and its potential effects on fetuses, children and adults.
WHO will also prioritize the development of vaccines and new tools to control mosquito populations, as well as improving diagnostic tests.
How to Treat Pregnant Women with Diagnoses of
Zika Virus Disease
No specific antiviral treatment is available for Zika virus
disease. Treatment is generally supportive and can include rest,
fluids, and use of analgesics and antipyretics . Fever should
be treated with acetaminophen. Although aspirin and
other nonsteroidal anti-inflammatory drugs are not typically
used in pregnancy, these medications should specifically be
avoided until dengue can be ruled out to reduce the risk for
hemorrhage .
In pregnant a woman with laboratory evidence of Zika
virus in serum or amniotic fluid, serial ultrasounds should
be considered to monitor fetal anatomy and growth every
3–4 weeks. Referral to a maternal-fetal medicine or infectious
disease specialist with expertise in pregnancy management is
recommended.
Zika virus: News and updates:
16 March 2016
First locally acquired cases are reported from Kosrae, Federated States of Micronesia; Dominica; and Cuba.
15 March 2016
A retrospective analysis of the Zika outbreak in French Polynesia, which occurred in 2013-2014, is published online in The Lancet. Using serological and surveillance data, the authors calculated the risk of microcephaly in fetuses and babies born to mothers infected with the Zika virus to be 1 in 100, or 1%. This study supports the hypothesis that Zika infection in the first trimester of pregnancy is associated with an increased risk of microcephaly
10 March 2016
Colombia reports two cases of microcephaly; both mothers and newborns tested positive for Zika virus by PCR. Results are pending for 13 more samples, among 27 cases of babies born with microcephaly in 2016.
10 March 2016
The United States reports two Guillain-Barre Syndrome (GBS) cases with confirmed Zika virus infection. The first case, an elderly man with a recent history of travel to El Salvador, died from sudden subarachnoid haemorrhage caused by a ruptured aneurysm. The second case, a male resident of Haiti in his 30s, was diagnosed after he travelled to the US for treatment. He recovered fully after 5 days of treatment in hospital.
9 March 2016
Venezuela provides an epidemiological update of the Zika outbreak in that country. A total of 16,942 suspected Zika cases have been reported. Of 801 samples tested by PCR, 352 (44%) were positive for Zika virus. Among the suspected cases are 941 pregnant women. A total of 226 samples from pregnant women were tested, and 153 (67.6%) were positive. No information is available about the outcome of these pregnancies, as the virus has not circulated long enough for these pregnancies to come to term.
Venezuela also reports 578 cases of Guillain-Barré syndrome, among which 235 have presented with symptoms of Zika virus infection. In addition, 1 case of facial paralysis and 10 cases of unspecified neurological disorders are PCR-positive for Zika virus.
9 March 2016
A letter published online in the New England Journal of Medicine describes a case in France of central nervous system infection with Zika virus associated with meningoencephalitis. The patient was an 81-year-old man who had been on a cruise in New Caledonia, Vanuatu, the Solomon Islands, and New Zealand. He was admitted to an intensive care unit and placed on a ventilator; cerebrospinal fluid tested positive for Zika virus. His neurologic condition improved without specific treatment, and he was discharged on day 17 of hospitalization.
8 March 2016
The second meeting of the Zika Emergency Committee affirms that clusters of microcephaly cases and other neurological disorders continue to constitute a Public Health Emergency of International Concern (PHEIC), and that evidence is increasing of a causal relationship of these disorders with Zika virus. WHO updates its travel recommendations to advise pregnant women not to travel to areas with ongoing Zika virus outbreaks; those whose partners live in or travel to such areas should practice safe sex or abstain for the duration of their pregnancy.
4 March 2016
The New England Journal of Medicine publishes online a study of Zika virus infection in 88 pregnant women in Rio de Janeiro, Brazil. 72 of these women (82%) tested positive for Zika virus in blood and/or urine. The most common symptoms were rash, joint pain, red eyes, and headache. Abnormalities of the fetus were detected by ultrasound in 12 Zika-positive women. These abnormalities included two fetal deaths, inability of the placenta to deliver adequate nutrients and oxygen to the fetus (placental insufficiency), poor fetal growth (fetal growth restriction), and injury to the central nervous system, including microcephaly. These findings add to the growing body of evidence linking Zika virus infection to fetal abnormalities.
3 March 2016
A case report published online in The Lancet describes a 15-year-old Zika-positive girl in Guadeloupe who developed acute myelitis (inflammation of the spinal cord), which caused severe back pain, numbness, and bladder dysfunction. This association suggests that Zika virus preferentially affects the nervous system.
- 2 March 2016
The United States confirms an additional 5 cases of sexually transmitted Zika virus infection, bringing the total six. All cases occurred in women with partners who recently returned from an area with ongoing Zika virus circulation. These additional cases suggest that sexual transmission of the virus may be more common than previously assumed.
2 March 2016
Samoa reports 10 additional cases of PCR-confirmed Zika virus infection, none of whom reported any recent international travel.
1 March 2016
France reports a probable case of sexual transmission of Zika virus, in the partner of a patient who had travelled to Brazil. The new case tested positive for Zika virus by PCR in saliva and urine; the partner tested positive by PCR in urine.
Information for travellers visiting Zika affected countries:
Travellers to areas with Zika virus outbreaks should be provided with up-to-date advice on potential risks and appropriate measures to reduce the possibility of exposure to mosquito bites and, upon return, should take appropriate measures, including safe sex, to reduce the risk of onward transmission.
Based on available evidence, there are no general restrictions on travel or trade with countries, areas and/or territories with Zika virus transmission. Countries reporting sporadic Zika infections in travellers arriving from affected countries pose little, if any, risk of onward transmission.
Pregnant women should be advised not to travel to areas of ongoing Zika virus outbreaks. Zika virus is spread by mosquitoes, and not by person-to-person contact, though a small number of cases of sexual transmission have been documented.
As a precautionary measure, some national governments may make public health and travel recommendations to their own populations, based on their assessment of the available evidence and local risk factors.
Zika has been found in human semen. Two reports have described cases where Zika has been transmitted from one person to another through sexual contact.
Until more is known about the risk of sexual transmission, all men and women returning from an area where Zika is circulating - especially pregnant women and their partners - should practice safer sex, including through the correct and consistent use of condoms, or abstaining from sex for the duration of the pregnancy.
All travellers, including pregnant women, going to an area where locally acquired Zika infection is occurring should adhere closely to steps that can prevent mosquito bites during the trip. These include:
- wearing clothes (preferably light-coloured) that cover as much of the body as possible;
- using insect repellent: repellents may be applied to exposed skin or to clothing, and should contain DEET, (diethyltoluamide) or IR 3535 or Icaridin. Repellents must be used in strict accordance with the label instructions;
- using physical barriers such as screens, closed doors and windows;
- sleeping under mosquito nets, especially during the day, when Aedesmosquitoes are most active;
- using physical barriers such mesh screens or treated netting materials on doors and windows; and
- identifying and eliminating potential mosquito breeding sites, by emptying, cleaning or covering containers that can hold even small amounts of water, such as buckets, vases, flower pots and tyres.
Zika MAC-ELISA (CDC)
- The Zika MAC-ELISA is a laboratory test to detect proteins the human body makes to fight a Zika virus infection. These proteins, called antibodies, appear in the blood starting 4-5 days after the start of illness and last for up to 12 weeks. In some people, they are present for longer than 12 weeks.
- The CDC Zika MAC-ELISA test has been authorized under the EUA for use by qualified laboratories in the U.S.designated by the CDC that are certified to perform high-complexity tests.
- Because of the possibility of false positive results in patients who were previously infected with viruses similar to the Zika virus (i.e., flaviviruses, such as dengue), under the terms of the EUA, positive and inconclusive results must be further tested by the CDC or by authorized laboratories in consultation with the CDC to confirm the presence of antibodies to Zika virus.
- Trioplex rRT-PCR (CDC)
- The CDC Trioplex rRT-PCR test has been authorized under the EUA for use by qualified laboratories in the U.S. designated by the CDC that are certified to perform high-complexity tests.
- The assay (test) is intended for use with specimens collected from individuals meeting CDC Zika virus clinical criteria (e.g., clinical signs and symptoms associated with Zika virus infection) and/or CDC Zika virus epidemiological criteria (e.g., history of residence in or travel to a geographic region with active Zika transmission at the time of travel, or other epidemiologic criteria for which Zika virus testing may be indicated as part of a public health investigation).
Emergency Use Authorization (EUA)
- While many people with Zika virus infection experience no symptoms, the virus can pose potentially serious risks to the public health. Access to a diagnostic test that can identify patients with Zika virus infections is critical to supporting response efforts and expanding domestic readiness. Potential links between Zika virus infection and neurological complications (i.e., Guillain-Barré Syndrome), as well as microcephaly and other poor pregnancy outcomes associated with Zika virus infection during pregnancy, have also increased the importance of having a diagnostic test available for Zika virus. As there are no commercially available diagnostic tests cleared or approved by the FDA for the detection of Zika virus infection, it was determined that an EUA is crucial to ensure timely access to a diagnostic tool.
- An EUA is a tool that FDA can use to allow the use of certain medical products for emergencies based on scientific data. The U.S. Secretary of Health and Human Services (HHS) has declared that circumstances exist to allow the emergency use of authorized diagnostic tests for Zika virus infection, such as the Zika MAC-ELISA
