Zika Virus Disease (ZVD) is a self-limiting acute disease caused by Zika Virus and transmitted through mosquito vectors. Zika virus was first identified in Uganda from rhesus monkeys in 1947 and isolated from humans in Uganda and Tanzania in 1952. only 14 disseminated cases of Zika virus disease were reported worldwide before 2007, when the first Zika virus outbreak was detected on the Pacific island of Yap in Micronesia, and the number of countries and regions where Zika virus infections and outbreaks were detected has increased since then. The first case of Zika virus disease was reported in Brazil in May 2015, and by the end of January 2016, 24 countries and regions in the Americas, including Brazil, had reported local infections. At the same time, several countries in Europe and North America reported finding imported cases, and Taiwan, China, also reported one imported case from Thailand. At the time of the Zika virus outbreak, the number of neonatal microcephaly cases increased significantly in Brazil and other countries, and available evidence suggests that neonatal microcephaly may be associated with Zika virus infection in pregnant women. The rapid spread of the epidemic and the possible causal relationship with microcephaly have caused widespread concern in the international community. Zhu Cuiyun, Department of Infection, Shanghai Public Health Clinical Center
The presence of Aedes aegypti mosquito, a vector that can transmit Zika virus, in some southern regions of China, and the imported epidemic of dengue fever, which has a similar mode of transmission, have continued to increase in recent years and have caused larger outbreaks in some southern provinces. With the increasingly close people to the relevant countries or regions, there is a risk of importation of Zika virus into China. In particular, the density of Aedes aegypti mosquitoes is high in the summer and autumn in the southern region of China, and once cases are imported, the possibility of local transmission and spread in local areas cannot be ruled out. To guide the prevention and control of Zika virus disease around the work, the development of this prevention and control program.
A. Overview of the disease
(A) pathogenesis
Zika virus belongs to the Flaviviridae family (Flavivirus) Flavivirus genus (Flavivirus), is spherical, about 40-70nm in diameter, with an envelope. The genome is a single-stranded positive-stranded RNA with a length of about 10.8 Kb. There are two genotypes, Asian and African, and the virus currently prevalent in South America is the Asian type. Zika virus and the same genus of flavivirus dengue virus, yellow fever virus and West Nile virus, there is a strong serological cross-reactivity. The virus can be cultured in mosquito-derived cells (C6/36), mammalian cells (Vero) and other cells to multiply and produce lesions.
The resistance of Zika virus is unknown, but the virus of the genus Flavivirus is generally not acid-resistant, heat-resistant, inactivated at 60 ℃ for 30 minutes, 70% ethanol, 1% sodium hypochlorite, lipid solvents, peroxyacetic acid and other disinfectants and UV irradiation can be inactivated.
(B) Epidemiology
1) Infectious source and vector
(1) Sources of infection: patients, latently infected persons and non-human primates infected with Zika virus are the possible sources of infection of the disease.
(2) vector: Aedes aegypti is the main vector of Zika virus, Aedes albopictus, Aedes africanus, Aedes aegypti and other mosquitoes of the genus Aedes may also transmit the virus.
According to monitoring, China and the transmission of Zika virus related to the species of Aedes aegypti and Aedes albopictus, which Aedes aegypti is mainly distributed in Hainan Province, Guangdong Leizhou Peninsula and Yunnan Province, Xishuangbanna Prefecture, Dehong Prefecture, Lincang City and other areas; Aedes albopictus is widely distributed in China’s Hebei, Shanxi, Shaanxi south of the vast region.
2. Transmission channels
(1) mosquito vector transmission for the main transmission route of Zika virus. Mosquito vector bite Zika virus infected people and be infected, and then through the bite of the virus to others.
(2) Human-to-human transmission
Mother-to-child transmission: Zika virus has been detected in the placenta of pregnant women, suggesting that Zika virus can be transmitted from mother to fetus through the placenta. In addition, pregnant women with Zika virusemia may transmit Zika virus to their newborns during delivery. Zika virus nucleic acid has been detected in breast milk, but there have been no reports of Zika virus infection of newborns through breastfeeding.
Blood and sexual transmission: Zika virus can potentially be transmitted through blood transfusion or sexual contact. To date, one case each of possible transmission by blood transfusion and sexual contact has been reported.
3. Population susceptibility
All types of people, including pregnant women, are generally susceptible to Zika virus. People who have been infected with Zika virus may be immune to reinfection.
4. Incubation period and transmission period
(1) incubation period: the incubation period of the disease is not known, limited data suggest that it may be 3-12 days.
(2) Infectious period: The infectious period of patients is not known, but some studies suggest that patients develop viremia early and are infectious.
5. Regional distribution
Zika virus disease is currently prevalent in countries and regions in the Americas, Africa, Southeast Asia, and the Pacific Islands.
(1) Regional distribution before 2014
From the discovery of the virus in 1947 until 2007, Zika virus disease was mainly disseminated, with only 14 confirmed cases of human infection.
From April to July 2007, 185 patients with symptoms of fever, headache, rash, conjunctivitis and arthralgia were seen in the Pacific island nation of Yap in Micronesia, of which 49 cases were confirmed as Zika virus infection, with no serious or fatal cases. In the following years, disseminated cases were reported in Thailand, Cambodia, Indonesia and New Caledonia in the Southeast Asia region.
In 2013-2014, an outbreak of Zika virus occurred in French Polynesia, located in the South Pacific, with approximately 10,000 reported cases, of which 70 were severe cases, including complications of neurological disorders (Gram-Barre syndrome, meningoencephalitis) or autoimmune diseases (thrombocytopenic purpura, leukopenia).
(2) Regional distribution since 2015
The first confirmed case of Zika virus infection was reported in Brazil in May 2015, and as of the end of January 2016, 24 countries and territories in the Americas have successively reported local cases of Zika virus infection, including: Colombia, Brazil, Bolivia, Barbados, Curaçao, Dominica, Ecuador, El Salvador, French Guiana, Guadeloupe, Guatemala, Guyana, Honduras , Mexico, Martinique, Nicaragua, Haiti, St. Martin, Puerto Rico, Paraguay, Panama, Suriname, U.S. Virgin Islands, and Venezuela.
Since 2015, imported cases of Zika virus have been found in the United States and Canada in North America, Taiwan, China in Asia, and Denmark, Finland, Germany, Italy, Portugal, the Netherlands, Spain, Sweden, the United Kingdom, and Switzerland in Europe.
To date, no cases of Zika virus disease have been reported in mainland China, Hong Kong and Macao.
6. Seasonal characteristics
The season of incidence is related to the seasonal growth of the local vector Aedes aegypti, with the peak of the epidemic occurring in summer and autumn. In tropical and subtropical areas, Zika virus disease can develop throughout the year.
(C) Clinical manifestations
Clinical symptoms include fever, rash (mostly maculopapular rash), arthralgia, muscle pain, conjunctivitis, etc. After infection with Zika virus, about 80% of people are insidiously infected, and only 20% of people develop the above clinical symptoms, which usually last for 2-7 days and then recover spontaneously; serious illness and death are rare.
Zika virus infection may lead to neurological and autoimmune complications in a small number of people, and infection in pregnant women may lead to microcephaly in newborns.
II. Diagnosis, reporting and treatment
(A) Diagnosis
Medical institutions at all levels should follow the “Zika Virus Disease Diagnosis and Treatment Protocol” to make the diagnosis of relevant cases. Care should be taken to differentiate the diagnosis from dengue fever, chikungunya fever and other diseases.
Confirmation of the first case of Zika virus infection found in each province should be confirmed by the CDC after laboratory testing and review. Serious cases, fatal cases, and specimens of indicated and first cases of outbreaks should be sent to the CDC laboratory for review and testing.
(ii) Reporting
When suspected, clinically diagnosed or confirmed cases of Zika virus disease are detected in medical institutions at all levels, they should be reported directly through the national disease surveillance information reporting management system within 24 hours, with the disease category “Zika virus disease among other infectious diseases” selected, and the region of origin indicated in the comment field if the case is imported. The uniform format is “imported from abroad/X country or region” or “imported from within/X province, X city, X county”.
The first case in each county (district) shall be reported to the local county health and family planning administrative department within 2 hours in accordance with the requirements of public health emergencies, and shall be reported online through the public health emergencies information reporting system. The health and family planning administrative department receiving the report should report to the people’s government at this level and the higher-level health and family planning administrative department within 2 hours.
(C) Treatment
The disease is generally self-limiting disease, there is no specific antiviral drugs for the disease, the main clinical symptomatic treatment.
Three, laboratory testing
The collection, packaging, transport and laboratory testing of cases and mosquito vector specimens are performed in accordance with the “Zika virus laboratory testing technical program”.
Zika virus disease detection methods include viral nucleic acid detection, IgM antibody detection, neutralizing antibody detection and virus isolation. Zika virus has a strong serological cross-reactivity with other viruses of the genus Flavivirus, and viral nucleic acid testing is currently used mainly.
When carrying out mosquito-borne Zika virus detection, virus nucleic acid testing is performed on captured adult Aedes aegypti mosquitoes or larvae.
Zika virus is classified as a Class III pathogen in China and laboratory testing should be conducted in a biosafety level II laboratory (BSL-2). Should be in accordance with the “pathogenic microbiological laboratory biosafety management regulations” and other relevant regulations require good biosafety protection work.
Fourth, epidemiological investigation
Upon receipt of a case report, the CDC should immediately organize professionals to conduct an investigation, analyze the source of infection, search for suspected cases, and assess the risk of further infection and epidemics.
When local infection cases are found, active search for cases and emergency surveillance of mosquito vectors should be conducted to analyze the dynamics of the epidemic, assess epidemiological trends, and propose timely and targeted control measures.
Detailed case investigations are conducted in accordance with the Zika Virus Disease Epidemiology Case Investigation Form for all disseminated cases and outbreaks of indicated cases, first cases, severe cases, and fatal cases, as well as those identified as necessary to identify the nature and extent of the epidemic. Subsequent cases occurring after the nature of the outbreak has been determined may use the “Zika Virus Disease Household Survey Registration Form” to collect brief epidemiological information.
(Source: http://www.nhfpc.gov.cn/jkj/s3577/201602/97bc31cc1767485290529a281d11c901.shtml.上海市公共卫生临床中心 edited by Cuiyun Zhu)