Zika virus is an acute infectious disease with a predominantly transmissible transmission mechanism. The disease is asymptomatic or is manifested by an increase in body temperature, general intoxication syndrome, pain in muscles, joints, conjunctivitis, rash. The main danger of infection is the formation of microcephaly and various neurological disorders in the fetus in case of infection of pregnant women, as well as persistent pathologies of the central nervous system in adults. Diagnosis is based on the detection of the virus itself in biological material, as well as specific antibodies in human blood serum. Etiotropic treatment has not been developed. Symptomatic therapy is carried out.
For the first time, the virus was isolated from the blood of a monkey that lived in the Zika forest in Uganda. Translated from the local dialect, “zika” means “thickets”. The endemic territories for this infectious disease are the countries of Central and South America, Africa, Southeast Asia, and the islands of the Pacific Ocean. In other States, examples of infection have also been recorded, but they are due to imported cases among travelers. Since 2015, about 4 million cases have been recorded. In 2016 WHO has declared an international health emergency due to an outbreak of the disease. Such alertness is associated with the pronounced teratogenic effect of the virus and the lack of specific treatment.
The receptivity is universal. Seasonality is not pronounced, but there is an increase in cases of infection during heavy rains, which is associated with an increase in the activity of mosquito vectors. With the development of global warming, the distribution area of the corresponding insects increases, which creates an even greater danger to humans. However, the virus cannot stand low temperatures. Therefore, the formation of persistent foci of fever in countries with a temperate climate is impossible, but imported cases can contribute to the development of outbreaks of morbidity in the summer.
The causative agent of the disease is an RNA–containing virus from the Flaviviridae family. Refers to arboviruses. The pathogen is quite stable in the environment. It remains in a freeze-dried state for up to 30 months. Phenol and low-percentage ethyl alcohol do not kill the microorganism, but it is quickly inactivated upon contact with ether, potassium permanganate solution. There are two virus lines: Asian and African. It is believed that the African form is parasitic in monkeys, and man is an accidental host. The Asian line was isolated from the majority of patients during epidemics in endemic areas.
The source of infection is monkeys and a sick person. Transmission of the disease is realized through a transmissible mechanism with the help of Aedes mosquitoes. Sexual, parenteral (with transfusion of blood components), transplacental, contact (with saliva) ways of infection are possible. The sexual pathway is realized only in men. Some authors suggest the possibility of aspiration infection in people with immunodeficiency. The virus is found in blood, saliva, urine, semen, breast milk, amniotic fluid during intrauterine infection. Zika virus transmission is dangerous during blood transfusions and organ and tissue transplants, because in most cases the disease is asymptomatic, there is no specific screening of donors, which can lead to iatrogenic infection of recipients.
The mechanism of development of this infectious disease is not fully understood. It is believed that the dendritic cells are the first to be affected at the bite site. Then the virus spreads with the blood flow to various organs and tissues. RNA replication occurs in infected cells of the human body. During the release of new virion particles from the cell, cytolysis of the affected structures develops. Morphological changes in skeletal musculature, myocardium (swelling of fibers, necrosis, proliferation of nuclei, disappearance of transverse striation) were detected during the study of micro-preparations. In experiments on laboratory animals, the high tropicity of the virus to the cells of the nervous system has been proven. In the case of intrauterine infection, the pathogen affects chorionic villi, placental vessels. Persistent fetal ischemia occurs. In addition, the Zika virus affects the mitotic activity of cells, which in turn leads to the formation of malformations.
Zika virus symptoms
In four out of five cases, the infection is asymptomatic. The incubation period is from 3 days to 2 weeks. A person becomes contagious a few days before the first symptoms appear. It is characterized by the presence of subfebrile fever, which lasts up to 5 days. There is weakness, lethargy, drowsiness, a feeling of malaise. Typically, the presence of myalgia, arthralgia, pain in the eyeballs, photophobia. Conjunctivitis often develops, swelling of small joints.
From the first day of the disease, a small itchy spotty-papular rash appears on the face, trunk, with subsequent possible spread throughout the body. Elements can increase in size, merge. Sometimes blisters with transparent contents form. Very rarely there are dyspeptic phenomena in the form of nausea, vomiting, diarrhea, feelings of heaviness, pain in the epigastrium. The duration of the disease is about 7 days.
In pregnant women and children infected by non-transplacental route, the disease proceeds with typical clinical symptoms. It is believed that after an infection, a stable immunity is formed, re-infection is unlikely.
The most serious complication in adults who have had Zika fever is the development of Guillain–Barre syndrome. There is no direct evidence of the connection of this neurological disorder with infection, however, according to studies in countries at risk, more than 90% of patients with Guillain–Barre syndrome had antibodies to the Zika virus.
The greatest danger is infection of women during pregnancy, especially during critical periods of fetal development. It is characterized by the miscarriage in the early stages, the formation of fetoplacental insufficiency, malformations, central nervous system damage with the development of microcephaly and malformation of the brain. In some cases, the appearance of pathology of the optic nerve is noted. Many authors associate the Zika virus with the development of meningoencephalitis, myelitis, hemorrhagic complications.
During an objective examination, no specific symptoms are detected. There is a rash, conjunctivitis, possibly swelling of small joints. This disease occurs most often in a mild form, so infected people rarely seek medical help. If you suspect Zika fever, you need to consult an infectious disease specialist. The following clinical and laboratory methods are used in diagnostics:
- Virus detection. Identification of the virus RNA by PCR with reverse transcription is carried out. This method is most informative from 3 to 7 days from the onset of the disease. Blood serum is used as the test material. Urine and semen are also studied in scientific research.
- Serological methods. The titer increase of specific IgM antibodies is determined in dynamics by the ELISA method. This method can give false positive results due to the possibility of cross-reactions with other representatives of flaviviruses.
- Ultrasound of the fetus. Sonography makes it possible to identify fetal malformations at the antenatal stage. Signs of microcephaly with a decrease in the circumference of the head, the presence of intracranial calcifications, ventriculomegaly are determined.
- Amniocentesis. There is no consensus on the need for a study of infected pregnant women. In the amniotic fluid, the Zika virus is detected 6-8 weeks after infection of the mother. In addition, the degree of pathogen release into the amniotic fluid depends on the maturity of the fetal kidneys.
WHO identifies the following criteria in the diagnosis of Zika fever: suspected, possible and confirmed cases. The alleged case is based only on the presence of clinical symptoms. A possible case includes the absence of a clinic, the detection of IgM in the blood, a burdened epidemiological history. The confirmed variant is characterized by the detection of virus RNA, IgM in a diagnostically significant titer, and the exclusion of infection with other flaviviruses. Differential diagnosis is carried out with yellow fever, dengue fever, chikungunya, rubella, malaria, HIV infection, leptospirosis, measles, rickettsiosis, infection with parvovirus, enterovirus, adenovirus, streptococcal infection.
Zika virus treatment
Specific drugs for the treatment of Zika virus infection have not been developed to date. Symptomatic treatment is carried out. Patients are recommended to drink copious amounts for the purpose of detoxification. With severe intoxication syndrome, infusion solutions are prescribed. Until dengue fever is excluded, NSAIDs should be avoided in order to prevent hemorrhagic complications. The use of nonsteroidal drugs in pregnant women up to 32 weeks may cause premature closure of the botal duct in the fetus. Antihistamines may be prescribed to reduce itching. Some authors recommend taking drugs that activate the immune system (ginseng, eleutherococcus).
Prognosis and prevention
The forecast is relatively favorable. In most cases, this viral infection occurs in mild forms. However, long-term consequences are associated with the development of severe neurological complications. The virus is also associated with the formation of malformations in the fetus and termination of pregnancy in the early stages of development. Statistical studies demonstrate a similar relationship.
Specific prevention has not been developed. Measures of non-specific protection include the use of repellents, mosquito nets in ventilated areas, long-sleeve clothing, the destruction of mosquito breeding sites, the use of air conditioners. Pregnant women and women planning pregnancy are not recommended to visit the countries of infection. An algorithm is being developed for screening all pregnant women who have returned from countries at risk for Zika fever. Men should use barrier methods of contraception when returning from traveling in endemic areas for at least a month, although there is evidence of the virus being isolated from semen for up to 60 days.