How is hepatitis B transmitted?

Hepatitis B refers to anthropogenous infections - the only source of infection is a person. In this case, the main reservoir is the "healthy" virus carriers, less important are patients with acute and chronic forms of the disease.

Currently in the world, according to incomplete data, there are about 350 million virus carriers, including more than 5 million live in Russia.

The prevalence of "healthy" carrier in different territories is not the same. It is accepted to distinguish territories with low (less than 1%) carrier of the virus in the population: USA, Canada, Australia, Central and Northern Europe; average (6-8%): Japan, Mediterranean countries, South-West Africa; high (20-50%): tropical Africa, the islands of Oceania, Southeast Asia, Taiwan.

In the CIS, the number of virus carriers also varies widely. A large number of carriers are registered in Central Asia, Kazakhstan, Eastern Siberia, and Moldavia - about 10-15%; in Moscow, the Baltic States, Nizhny Novgorod - 2.5-1.5%. The frequency of detection of markers of HBV infection in children is higher than in adults, in men more than in women. It should also be noted that the data on the frequency of "healthy" carrier in our country can be considered only indicative, since not all authors and not in all territories used highly sensitive methods of research to indicate markers of HBV virus infection.

Large fluctuations in the frequency of virus carrying occur not only in different territories, but also in different groups of people living in the same territory. So. According to our clinic, HBsAg in the child's home is found in 26.2% of children, in the boarding school - in 8.6, among children with acute surgical pathology - in 5.4% of cases, while in the group of donated donors only in 2%. The prevalence of HBV virus infection among children suffering from various chronic diseases is especially high: diabetes, hemoblastosis, tuberculosis, pyelonephritis, etc. Our studies have shown that among patients oncological hospital with a single screening examination HBsAg is found in 26% of cases, while its frequency detection depends on the method of indication: when using a low-sensitivity method - the reaction of passive hemagglutination (RPHA) - HBsAg is detected in 10%, and high sensitivity the EIA method - in 26% of cases.

The danger of "healthy" virus carriers as a source of infection is primarily that they, as a rule, remain unrecognized, keep active way of life and do not observe measures of anti-epidemic alertness. From this point of view, patients with manifest forms of the disease are less dangerous to others, since these forms are mostly diagnosed early and patients are isolated, which reduces the epidemiological significance of these cases. At the same time, patients with chronic hepatitis B often serve as a powerful source of infection, especially in closed children's groups and family. As studies have shown, the frequency of detecting hepatitis B markers in parents of children with chronic hepatitis B is 80-90%, including 90.9% for mothers, 78.4% for fathers, and 78.5% for siblings.

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How can you get hepatitis B?

In all infected with the hepatitis B virus, regardless of the nature of the process ("healthy" carriers, patients with acute, chronic hepatitis), HBsAg - the main marker of infection - is found in virtually all biological environments of the body: blood, semen, saliva, urine, bile, tears, breast milk, vaginal secretion, cerebrospinal fluid, synovial fluid. However, only blood, seeds and saliva present a real epidemiological danger, where the concentration of the virus is much higher than the threshold. The greatest danger is the blood of the patient and the virus carrier. It is shown that the infectivity of blood serum containing HBV persists even when it is diluted to 107-108. The frequency of detection of HBsAg in various biological media is directly dependent on its concentration in the blood. In this case, only in blood, the concentration of the virus is almost always higher than the infectious dose, whereas in other biological fluids the content of full-fledged virions relatively rarely reaches a threshold value. It is shown that in patients with various clinical forms of hepatitis B, it is possible to detect the virus using highly sensitive methods in saliva and urine in only half the cases and extremely rarely in breast milk.

Hepatitis B transmission routes

Transmission of the hepatitis B virus is carried out exclusively parenterally: by transfusion of infected blood or its preparations (plasma, erythrocyte mass, albumin, protein, cryoprecipitate, antithrombin, etc.), using poorly sterilized syringes, needles, cutting tools, surgical procedures, dental treatment, endoscopic examination, duodenal probing, scarification, tattooing and other manipulations, in which the integrity of the skin and mucous membranes is impaired. Because the infecting dose is extremely small, the day of infection is sufficient inoculation of negligible amounts of virus-containing blood (about 0.0005 ml). The risk of infection increases dramatically with the transfusion of blood and its components. According to our clinic, infection of children with acute hepatitis B in 15.1% of cases occurs with blood or plasma transfusions, in 23,8 - with various parenteral manipulations, in 20,5 - with surgical interventions, in 5,3 - with intravenous administration and only in 12.8% of cases - through household contact. In patients with chronic hepatitis, infection occurs in most cases (63.7%) with parenteral interventions, often with household contact (24.5%) and less often with blood transfusions (9.3%).

The natural ways of transmission of hepatitis B include transmission of the virus in sexual contact and vertical transmission from the mother to the child. The sex route of transmission should also be considered parenteral, since infection occurs through inoculation of the virus through microtraumas of the skin and mucous membranes of the genital organs.

Vertical transmission of the hepatitis B virus is carried out mainly in regions with a high prevalence of virus carrying. A mother can infect a child if she is a carrier of a virus or a patient with hepatitis in the last trimester of pregnancy. Infection of the child can occur transplacental, during labor or immediately after. Transplacental transmission is relatively rare - no more than 5-10% of cases. However, the risk of infection increases dramatically in the case of detection in the blood of the mother HBeAg, especially its high concentration.

Infection of children from mothers who are carriers of the hepatitis B virus occurs predominantly during childbirth due to contamination by blood-containing amniotic fluid through the macerated skin and mucous membranes of the child or through passage through the birth canal. In rare cases, the child becomes infected immediately after birth, in close contact with the infected mother . The transmission of infection in these cases is carried out through microtrauma, that is, parenterally, and, possibly, with breastfeeding. In this case, the infection of the child does not occur through the mother's milk, but parenterally through the ingestion of the mother's blood in connection with possible nipple cracks in the macerated mucous cover of the child's mouth.

The risk of perinatal infection of a child from a mother with hepatitis B or a virus carrier can reach 40%, according to WHO materials, in some countries up to 25% of all virus carriers are infected perinatally. In this case, most children develop primary chronic hepatitis. The opinion is expressed that in the world there are already more than 50 million patients with chronic hepatitis B infected with a perinatal route.

In recent years, the contact-household way of transmission of hepatitis B has become increasingly important. At its core, it is the same parenteral route of infection, as infection occurs as a result of the entry of virus-containing biological material (blood, etc.) into the damaged skin and mucous membranes. Transmission factors may include toothbrushes, toys, manicure accessories, razors, etc.

Most often, infection through close domestic communication occurs in the family, at the children's homes, boarding schools and other closed institutions, while the spread of infection is facilitated by crowding, low sanitary and hygienic living standards, low culture of communication, the decisive factor can be the length of communication with the source of infection. In families of children with chronic hepatitis B, markers of viral hepatitis B were found in close relatives (father, mother, brothers, sisters) in 40% of cases in the first study, and in 80% in 3-5 years.

In adults, hepatitis B infection occurs sexually (60-70%), with the injection of psychotropic substances, as well as with various medical manipulations.

Previous assumptions about the existence of other ways of transmission of hepatitis B (water, fecal-oral, through blood-sucking insects) have not been confirmed at present.

Theoretically, it is possible to allow the transmission of the hepatitis B virus through insect bites (mosquitoes, mosquitoes, bugs, etc.). This route of transmission was not confirmed, despite the fact that some researchers were able to detect hepatitis B virus markers in bloodsucking insects immediately after the bloodsucking. However, given that replication of the virus in the body of blood-sucking insects does not occur, infection, if possible, only at the time of their crushing, that is, by mechanical means by rubbing the virus-containing blood into the damaged skin.

Thus, hepatitis B can be considered a blood infection, in which infection occurs exclusively parenterally.

The susceptibility of the population to the hepatitis B virus is likely to be universal, but the outcome of a person's meeting with a virus is often an asymptomatic infection. The frequency of atypical forms does not lend itself to accurate accounting, but judging by the detectability of seropositive people, it can be said that for every case of manifest hepatitis B dozens and even hundreds of subclinical forms occur.

The opinion is expressed that the prevalence of subclinical forms is associated with the leading role of natural ways of transmission of infection, in which the infectious dose, as a rule, is extremely small. The leading role of the infecting dose can be evidenced by the fact that when infecting with blood transfusions, manifestly, including practically all malignant, forms of the disease develop, whereas perinatal infection and everyday contact form a chronic sluggish infection.

A high incidence of hepatitis B was registered in both adults and children, in the late 90s of the XX century. At the beginning of the 21st century, there has been a sharp decline in the incidence of hepatitis B in our country, which can be attributed to widespread mass vaccine prophylaxis.

Nevertheless, a significant proportion of hepatitis B in the overall structure of acute viral hepatitis in Russia remains.

According to Rospotrebnadzor, in 2007 in Russia there was a very high incidence of hepatitis B in children of the first year of life, which was 1.65 for 105 of this contingent and exceeded by 3.6 times the total incidence of children (under the age of 14), equal to 0, 45 per 105 children's population. This fact arose against a background of a sharp decline in the incidence of hepatitis B in children from 1998 to 2007, from 10.6 to 0.45 per 105 population.

It should be emphasized, however, that in recent years, the level of the incidence of hepatitis B in young children has been steadily declining due to preventive measures (selection of donors, reduction of indications for blood transfusions, general alertness). In 2000, the incidence rate in Russia among the children of the first. 2 years of life was 10.5, whereas in 1987 - 27.3, and in 1986 - 35.1.

According to the research, children of the first year of life in 20% of cases are infected with blood transfusions and its components, in 10 - with parenteral manipulation, in 60% - in childbirth, and only in 10% of cases it is possible to assume antenatal infection. Presumably, the place of infection of children in 51.4% of cases became maternity hospitals and hospital hospitals, in 16.3% - children's polyclinics.

Seasonal fluctuations in the incidence of hepatitis B are uncharacteristic. When infected as a result of preventive vaccinations, mass medical examination, transfusion of infected blood or its preparations from one package, several children may experience several cases of hepatitis B. In closed children's institutions and families, there may be repeated cases, which is usually associated with a prolonged stay of the source of infection in the child collective and possible contamination by the domestic way of new people.

As a result of acute hepatitis B, persistent life-long immunity is formed. The occurrence of recurrent disease is unlikely.