How is hepatitis A spread?

Source of hepatitis A infection

Hepatitis A is a typical anthroponous infection, that is, the source of infection is a person with an obvious or worn out form of the disease. Indication of other authors on the findings of the hepatitis A virus in some species of monkeys can not shake confidence in the anthroponotic nature of the infection, since, on the one hand, these findings are rare, and on the other hand, the possibility of infection of monkeys from humans is not excluded.

The main role in the active maintenance of the epidemic process is played by patients with hepatitis A, especially atypical forms - blurred, jaundiced and subclinical. Remaining in most cases unrecognized, patients with these forms continue an active way of life, visit organized children's groups and thus become hidden - and, due to this, often a powerful - source of infection. It must also be taken into account that even with incomplete registration, the number of patients with erased, jaundiced and subclinical forms is much higher than the number of patients with typical icteric forms of the disease. Especially it is characteristic for children's organized collectives.

The greatest epidemiological danger is represented by patients from the end of the incubation period and throughout the entire pre-zheltushnogo period. The duration of the active replication and virus isolation phase varies from 15 to 45-50 days, most often does not exceed 2-3 weeks. With the appearance of jaundice, the concentration of the virus in the blood rapidly decreases, and it usually can not be detected by conventional methods of investigation. With the use of highly sensitive methods of detection of the hepatitis A virus antigen, it is established that at the end of incubation and prolongation it is determined practically in all patients, in the first week of icteric period only in half, in the second week at 20-21%, in the third week at 5% patients. The same data were obtained by numerous researchers on a large clinical material and experimental hepatitis in animals (marmosets). It is also important to take into account the fact that the significant difference in the frequency of detection of the hepatitis A virus antigen in the feces of patients with various forms of hepatitis A (icteric, jaundice, blurred, inapparant) has not been abolished. This once again confirms the enormous importance of atypical forms of the disease in maintaining a continuous epidemic process in hepatitis A.

Mechanisms of transmission of hepatitis A

The causative agent of hepatitis A is transmitted exclusively by the fecal-oral route, through infected foods, water and through household contact. The virus is excreted only with feces, and it gets into food usually when the elementary rules of hygiene are violated at the time of its processing and preparation; water contamination occurs by contamination of water sources by household discharges. In the literature, food, water, contact-household outbreaks of hepatitis A are widely described among both adults and children. Various food products (oysters, orange juice, dried melon, milk, ice cream, cottage cheese, etc.), water from open water bodies, wells, irrigation ditches acted as factors of infection transmission. Water flares are usually characterized by an explosive nature, when during a short time at the same time there are massive diseases combined by the use of water from a single source.

The role of flies as a factor in the transmission of infection appears to be exaggerated, but in conditions of low sanitary culture and crowding, flies can carry the infectious agent to food or drinkable water. Major epidemics caused by a supposedly engine factor were mainly described before the use of highly sensitive specific methods for verifying hepatitis A and therefore need a critical reassessment. The same can be said for the airborne droplet transmission pathway for hepatitis A virus. Studies of recent years have not confirmed the possibility of finding the hepatitis A virus on the mucous membranes of the respiratory tract, which excludes the airborne pathway of infection transmission.

Parenteral mechanism of infection transmission is allowed, which, naturally, can occur only if the blood of the patient containing the virus enters the bloodstream of the recipient. Theoretically it is. Of course, it is possible, but it is realized, apparently extremely rarely because of the instability of the virus in the blood.

The transmission of hepatitis A virus from mother to fetus by transplacental virtually all researchers is excluded due to the inability of the hepatitis A virus to overcome the transplacental barrier

Hepatitis A can rightly be called "sickness of dirty hands". This is the way that epidemic foci of hepatitis A arise in kindergartens, schools and other organized collectives, as well as on playgrounds and in isolated families. Diseases occur simultaneously in small groups with a consistent involvement in the epidemic process of new contingents of susceptible children. In schools, pioneer camps, out-of-school kindergartens, infection of the hands often occurs in public places (public toilets, playgrounds, canteens), as well as in contact with door handles, handrails, toys of general use, etc. With such a path of infection, it is not easy to establish the source of infection, that is why with hepatitis A a fairly high percentage of sporadic morbidity. This is also facilitated by a low infectious dose of the causative agent of the disease.

Hepatitis A is characterized by seasonal ups and periodicity of morbidity. Seasonal rises are more distinctly traced among children's contingents. Increase in the incidence falls on the autumn-winter period with a predominant peak in October-December, which is characteristic of the fecal-oral mechanism of transmission of infection. Relatively later onset of the incidence peak, compared with classical gastrointestinal infections (shigellosis, salmonellosis, etc.) can be explained by a longer incubation period in hepatitis A. The rise in the incidence of hepatitis A in the autumn-winter period can also be explained by the sudden increase in mass contacts in connection with the beginning of schooling, the increase in this time of the year, the filling of children's preschool institutions, the accumulation of children in enclosed spaces, which, as is known, make it difficult to realize the general hygiene measures.

Periodic incidents of morbidity are characterized by strict cyclicity, they are repeated at an interval of 10-12 years. On the territory of the former USSR, the rise in morbidity was observed in 1960-1962, then gradually decreased until 1970, but since 1971 the incidence began to increase gradually and reached a maximum in 1983. The reason for this periodicity is the fluctuation of collective immunity, which is confirmed by the results of a study of the dynamics of accumulation of specific antibodies in both children in the age aspect and in adults. Currently, the incidence of hepatitis A in our country has a pronounced downward trend.

Susceptibility of the hepatitis A virus

In experiments on volunteers it was shown that the susceptibility to the hepatitis A virus is determined solely by the presence or absence of specific antibodies. The dose and virulence of the pathogen, as well as the genotypic and phenotypic heterogeneity of some people with regard to hepatitis A infection, are important. The index of contagiosity in hepatitis A ranges from 0.2 to 0.8 (0.4 on average), that is, from 100 contact children , not infected with hepatitis A, get sick about 40. In children of the first year of life, the contagiosity index approaches 0 because of the presence of transplacental immunity. At the age of 3 to 7-9 years, the contagious index rises to 0.6-0.8, in adults it drops to 0.2 or more.