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, reported local cases of infection. 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.
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 is a family of flaviviridae (Flavivirus) Flavivirus (Flavivirus), spherical, about 40-70 nm in diameter, with an envelope. The genome is a single-stranded positive-stranded RNA, with a length of about 10 or 8 Kb. It is divided into 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 viruses of the genus Flavivirus are generally not acid-resistant, heat-resistant, inactivated at 60°C for 30 minutes, and inactivated by 70% ethanol, 1% sodium hypochlorite, lipid solvents, disinfectants such as peroxyacetic acid, and UV irradiation.
(B) Epidemiology.
1.Infectious sources and vectors
(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 Hebei, Shanxi and Shaanxi south of China’s vast regions.
2, the transmission route
(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 infection period
(1) incubation period: the incubation period of the disease is not known, limited information suggests that it may be 3-12 days.
(2) Infectious period: the infectious period of patients is not known, some studies have shown that patients produce viraemia early and have infectious.
5.Regional distribution
Zika virus disease is currently prevalent in countries and regions such as 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 diagnosed 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.
So far, 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.
(iii) Clinical manifestations.
Clinical symptoms include fever, rash (mostly maculopapular rash), arthralgia, muscle pain, conjunctivitis, etc. After Zika virus infection, about 80% of people are recessively infected, and only 20% of people develop the above clinical symptoms, which usually last for 2-7 days and then recover spontaneously; severe illness and fatal cases 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
In accordance with the “Zika virus laboratory testing techniques program” (Appendix 1) for the collection, packaging, transport and laboratory testing of cases and mosquito vector specimens.
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 professional staff 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 (Appendix 2) for all disseminated cases and cases indicated for outbreaks, first cases, severe cases, fatal cases, and those identified for investigation as needed to identify the nature and extent of the epidemic. Subsequent cases occurring after the nature of the outbreak has been determined can use the “Zika Virus Disease Household Survey Registration Form” (Appendix 3) to collect brief epidemiological information.
V. Prevention and control measures
(A) Prevention of importation.
1. Pay attention to the international epidemic situation
Closely track information on the progress of the international Zika virus disease epidemic, dynamic risk assessment, to provide a basis for the development and adjustment of local prevention and control strategies and measures.
2.Issue travel health tips as needed
Local health planning departments assist foreign affairs, commerce, tourism and entry-exit inspection and quarantine departments to do a good job of public education and health tips for travelers to Zika virus disease endemic areas and overseas Chinese citizens.
3. Do a good job in port health quarantine
Once the health and quarantine departments found suspected cases, should promptly notify the health and family planning departments, and jointly do a good job in the investigation and disposal of the epidemic.
(B) Case monitoring and management.
1, case monitoring and early detection
Medical institutions at all levels found fever, rash, muscle and joint pain patients, should pay attention to understand the epidemiological history of patients (travel history of endemic areas), consider the possibility of the disease, and timely sampling for testing. In addition, the possibility of Zika virus infection should also be considered for mothers with newborns presenting with microcephaly who have a suspicious epidemiological history.
2.Epidemiological investigation
Conduct case investigation of relevant cases, focusing on the patient’s activity history 2 weeks before the onset of the disease to identify suspected infection sites and search for sources of infection; also investigate the activity history one week after the onset of the disease, conduct case search, and assess the risk of infection and epidemic.
3.Case search
For imported cases, travel history should be traced in detail, focusing on searching among those who travel with them. If the case has been active in the county (district) from the time of entry to 1 week after the onset of the disease, the suspected case should also be searched in their living and working areas.
In the case of local infection epidemic cases, the case residence or a number of households adjacent to it, the case’s workplace and other places of activity as the center, reference Aedes aegypti activity range to delineate the spatial extent within a radius of 200 meters as the core area, an infected person can be delineated multiple core areas, search for cases in the core area. Can be based on urban or rural areas or different building types, speculation Aedes aegypti activity range, appropriate to expand or narrow the search radius.
4.Case management
The acute phase of the case must take anti-mosquito isolation measures, anti-mosquito isolation period from the onset of not less than 7 days, and should continue until the fever symptoms subside. Serious cases should be hospitalized.
Medical and health personnel in the treatment and epidemiological investigation, should take standard protection. On the basis of good case management and general nosocomial infection control measures, health care institutions should implement anti-mosquito and mosquito control measures to prevent nosocomial transmission.
(C) vector surveillance and control.
There are vector distribution areas, in addition to the above work, but also need to do a good job of vector monitoring and control work.
1, daily monitoring and control
Health and family planning administrative departments at all levels are responsible for leading and organizing local disease prevention and control agencies to carry out community-based Aedes aegypti mosquito density monitoring, including Aedes aegypti species, density, seasonal growth and so on. Daily monitoring scope, methods and frequency requirements as dengue fever, can refer to the “dengue fever vector Aedes aegypti monitoring guide” in the routine monitoring.
When the vector Aedes aegypti Brett index and ovitrap index exceeds 20, the local government should be promptly requested to organize a patriotic health campaign to remove indoor and outdoor breeding sites of various vectors of Aedes aegypti and carry out preventive mosquito control campaigns to reduce the density of Aedes aegypti, in order to reduce or eliminate the risk of Zika virus disease and other mosquito-borne disease outbreaks.
2.Emergency monitoring and control
When imported or local cases of Zika virus disease are found during the Aedes mosquito activity season, emergency surveillance should be initiated. Aedes vector emergency surveillance area, methods and frequency requirements with dengue fever, can refer to the “dengue vector Aedes mosquito surveillance guidelines” in the emergency surveillance.
When there are cases of Zika virus disease and the epidemic site as the center of a 200-m radius Brett index or ovitrap index ≥ 5, the alert area (core area outreach 200-m radius) ≥ 10, or Brett index or ovitrap index greater than 20, the emergency vector Aedes aegypti control should be initiated.
Aedes aegypti emergency control points include: good community mobilization, patriotic health campaign, do a good job of mosquito breeding ground cleanup; education of the masses to do a good job of personal protection; to take accurate emergency adult mosquitoes at the epidemic site to kill, etc., through a comprehensive range of Aedes aegypti prevention and control measures, as soon as possible, the Brett index or ovitrap index control in 5 or less.
(D) publicity and communication.
Areas at risk of epidemic should take a variety of effective forms to carry out health education activities in an easy-to-understand manner. Publicity points include: Zika virus disease is transmitted by the bite of Aedes aegypti mosquitoes (commonly known as Aedes aegypti or Anopheles mosquitoes); Aedes aegypti mosquitoes breed in water tanks, water pots, tires, flower pots, vases and other containers of stagnant water; removing stagnant water, turning over pots and pans, and removing mosquito breeding sites can prevent Zika virus disease epidemics; in areas where epidemics occur, wear long-sleeved clothing and pants, apply anti-mosquito water to exposed parts of the body, use mosquito repellent or use mosquito nets, mosquito nets, etc. Prevent mosquito bites.
In addition to general travel health tips, pregnant women and women planning to become pregnant should be reminded to be cautious when traveling to countries or regions where Zika virus disease is endemic, and to take strict personal protective measures against mosquito bites if they do need to travel to these countries or regions. If they suspect possible Zika virus infection, they should seek prompt medical attention, report their travel history voluntarily, and receive medical follow-up.
(V) Training and laboratory capacity building.
1. Strengthen medical staff training and improve disease identification ability
Carry out training of medical personnel on diagnosis and treatment to improve disease diagnosis and identification. Key areas should carry out intensive training of grassroots medical personnel on Zika virus disease-related knowledge before the annual epidemic season, in conjunction with the prevention and control of dengue fever and chikungunya fever, to enhance awareness of Zika virus disease and timely detection and reporting of suspected Zika virus infection cases.
2. Establish Zika virus detection capacity
Establish and gradually promote laboratory testing techniques for Zika virus. The provincial centers for disease prevention and control should establish relevant techniques and methods for laboratory testing as soon as possible, make good reserves of laboratory techniques and reagents, and gradually improve the laboratory testing capacity of the grassroots centers for disease prevention and control for the disease to respond to possible outbreaks.