Zika virus disease is a self-limiting acute infectious disease caused by Zika virus and is transmitted mainly by the bite of Aedes aegypti mosquito. Clinical features are mainly fever, rash, arthralgia or conjunctivitis, and rarely cause death. The World Health Organization (WHO) believes that microcephaly and Guillain-Barré syndrome (GBS) in newborns may be associated with Zika virus infection. Zika virus disease is predominantly endemic in tropical and subtropical regions of the world. 1952, the virus was isolated from humans in Uganda and Tanzania. Since then, disseminated cases have been reported in several countries, and the first outbreak of Zika virus occurred in 2007 on the island of Yap in the Western Pacific country of Micronesia. As of January 2016, there is evidence of Zika virus transmission in at least 45 countries in Africa, Asia, and the Americas, with the most severe outbreak in Brazil.
I. Pathogenesis Zika virus is a mosquito-borne virus
It was first discovered in 1947 in rhesus monkeys in Uganda. It belongs to the genus Flavivirus of the family Flaviviridae, and is a single-stranded positive-stranded RNA virus with a diameter of 40-70 nm and an envelope containing 10,794 nucleotides and encoding 3419 amino acids. According to the genotype, it is divided into African type and Asian type, and the epidemic in America is the Asian type.
The resistance of Zika virus is unknown, but the virus of the genus Flavivirus is generally not acid-resistant, heat-resistant. 60 ℃ for 30 minutes can be inactivated, 70% ethanol, 1% sodium hypochlorite, lipid solvents, peroxyacetic acid and other disinfectants and ultraviolet radiation can be inactivated.
Second, epidemiological characteristics 1 infectious source
Patients, latently infected persons and non-human primates infected with Zika virus are the possible sources of infection of the disease.
1, the transmission route
The bite of Aedes aegypti mosquitoes with the virus is the most important route of transmission of the disease. The vector is mainly Aedes aegypti, Aedes albopictus, Aedes africanus and Aedes aegypti may also transmit the virus. It can also be transmitted from mother to child, including intrauterine infection and infection during delivery. Zika virus nucleic acid can be detected in breast milk, but there have been no reports of infection of newborns through breastfeeding. Blood-borne transmission and sexual transmission are rare.
According to monitoring, China has with the transmission of Zika virus Aedes species mainly Aedes aegypti and Aedes albopictus, which Aedes aegypti is mainly distributed in Hainan Province, Guangdong Province, 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.Population susceptibility
The population is generally susceptible. People who have been infected with Zika virus may have immunity to reinfection.
Clinical manifestations of Zika virus disease incubation period is still unclear, the available information shows that 3-12 days. Only 20% of people infected with Zika virus develop symptoms, and the symptoms are mild, mainly manifested as fever, rash, and may be accompanied by non-purulent conjunctivitis, muscle and joint pain, general malaise and headache, a few patients may develop abdominal pain, nausea, diarrhea, mucosal ulcers, skin itching, etc.. The symptoms last for 2-7 days and have a good prognosis; severe illness and death are rare.
Pediatric cases of infection may also present with neurological, ocular, and hearing changes. Zika virus infection in pregnant women may lead to microcephaly and even fetal death in newborns.
Cases of Green-Barre syndrome associated with Zika virus infection have been reported, but the causal relationship between the two is not clear.
IV. Laboratory tests
1.General examination
Blood routine: some cases may have leukocytopenia and thrombocytopenia.
2, serological examination.
(1) Zika virus IgM detection: enzyme-linked immunosorbent assay, immunofluorescence assay, etc. for detection.
(2) Zika virus neutralizing antibody detection: the use of empty spot reduction neutralization test to detect blood neutralizing antibody. Double copies of serum should be collected for testing in the acute and recovery periods as far as possible.
Zika virus antibodies and the same genus of flavivirus dengue virus, yellow fever virus and West Nile virus antibodies have a strong cross-reactivity, easy to produce false positives, in the diagnosis should pay attention to differentiation.
3.Ethiological examination.
(1) viral nucleic acid detection: the use of fluorescent quantitative RT-PCR detection of Zika virus.
(2) viral antigen detection: the use of immunohistochemical method to detect Zika virus antigen.
(3) Virus isolation culture: specimens can be inoculated in mosquito-derived cells or mammalian cells and other methods for isolation culture, and can also be used for virus isolation by intracerebral inoculation of mammary rats.
V. Diagnosis and differential diagnosis
1.Diagnosis basis
Based on epidemiological history, clinical manifestations and relevant laboratory tests.
2.Case definition
3.Suspected cases: consistent with epidemiological history and corresponding clinical manifestations.
(1) Epidemiological history: travel or residence in areas where Zika virus infection cases are reported or endemic within 14 days before the onset of the disease.
(2) clinical manifestations: fever, rash, arthralgia or conjunctivitis that are difficult to explain by other causes.
4, clinical diagnosis of cases: suspected cases and positive Zika virus IgM antibody test.
5, confirmed cases: suspected cases or clinically diagnosed cases by laboratory tests meet one of the following circumstances.
(1) Zika virus nucleic acid test positive.
(2) isolation of Zika virus.
(3) recovery period serum Zika virus neutralizing antibody positive or titer than the acute period is more than four times higher, while excluding dengue, B brain and other common flavivirus infection.
3.Differential diagnosis.
1, mainly with dengue fever and chikungunya fever for differential diagnosis.
2.Other: Differentiate from microviruses, rubella, measles, enterovirus, rickettsial disease, etc.