How is hepatitis B transmitted?

Hepatitis B is an anthroponotic infection - the only source of infection is a person. The main reservoir is "healthy" virus carriers, patients with acute and chronic forms of the disease are of lesser importance.

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

The prevalence of "healthy" carriage varies in different territories. It is customary to distinguish territories with low (less than 1%) carriage of the virus in the population: the USA, Canada, Australia, Central and Northern Europe; average (6-8%): Japan, Mediterranean countries, Southwest Africa; high (20-50%): Tropical Africa, the islands of Oceania, Southeast Asia, Taiwan.

In the CIS, the number of virus carriers also fluctuates widely. A large number of carriers are registered in Central Asia, Kazakhstan, Eastern Siberia, Moldova - about 10-15%; in Moscow, the Baltic States, Nizhny Novgorod - 2.5-1.5%. The frequency of detection of HBV infection markers 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" carriage in our country can be considered only approximate, since not all authors and not in all territories used highly sensitive research methods to indicate HBV infection markers.

Large fluctuations in the frequency of virus carriage are detected not only in different territories, but also in different groups of people living in the same territory. Thus, according to our clinic, HBsAg is detected in 26.2% of children in the orphanage, in 8.6% in the boarding school, among children with acute surgical pathology - in 5.4% of cases, while in the group of unpaid donors only in 2%. The prevalence of HB virus infection is especially high among children suffering from various chronic diseases: diabetes mellitus, hemoblastoses, tuberculosis, pyelonephritis, etc. Our studies have shown that among patients in an oncology hospital, HBsAg is detected in 26% of cases during a single screening examination, and the frequency of its detection depends on the method of indication: when using a low-sensitivity method - the passive hemagglutinin reaction (PHA) - HBsAg is detected in 10%, and by the highly sensitive ELISA method - in 26% of cases.

The danger of "healthy" virus carriers as a source of infection is primarily that they usually remain unrecognized, maintain an active lifestyle and do not observe anti-epidemic alertness measures. From this point of view, patients with manifest forms of the disease pose less danger 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 families. As studies have shown, the frequency of detection of hepatitis B markers in parents of children suffering from chronic hepatitis B is 80-90%, including 90.9% in mothers, 78.4% in fathers, and 78.5% in siblings.

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How can you get hepatitis B?

In all people 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 detected in almost all biological environments of the body: in blood, semen, saliva, urine, bile, tears, breast milk, vaginal secretions, cerebrospinal fluid, synovial fluid. However, only blood, semen and saliva, where the concentration of the virus is significantly higher than the threshold, pose a real epidemiological danger. The greatest danger is the blood of a patient and a virus carrier. It has been shown that the infectivity of blood serum containing HBV is preserved even when diluted to 107-108. The frequency of detection of HBsAg in various biological environments is directly dependent on its concentration in the blood. At the same time, only in the blood is the concentration of the virus almost always higher than the infective dose, while in other biological fluids the content of full-fledged virions relatively rarely reaches the threshold value. It has been shown that in patients with various clinical forms of hepatitis B, the virus can be detected using highly sensitive methods in saliva and urine only in half of the cases and extremely rarely in breast milk.

Routes of transmission of hepatitis B

The hepatitis B virus is transmitted exclusively parenterally: by transfusion of infected blood or its preparations (plasma, red blood cell mass, albumin, protein, cryoprecipitate, antithrombin, etc.), use of poorly sterilized syringes, needles, cutting instruments, surgical interventions, dental treatment, endoscopic examination, duodenal intubation, scarification, tattooing and other manipulations that violate the integrity of the skin and mucous membranes. Since the infectious dose is extremely small, inoculation of negligible amounts of virus-containing blood (about 0.0005 ml) is sufficient for infection. The risk of infection increases sharply with transfusion of blood and its components. According to our clinic, infection of children with acute hepatitis B in 15.1% of cases occurs through blood or plasma transfusion, in 23.8% - through various parenteral manipulations, in 20.5% - through surgical interventions, in 5.3% - through intravenous drug use and only in 12.8% of cases - through household contact. In patients with chronic hepatitis, infection in most cases (63.7%) occurs through parenteral interventions, often through household contact (24.5%) and less often through blood transfusions (9.3%).

Natural routes of transmission of hepatitis B include transmission of the virus through sexual contact and vertical transmission from mother to child. The sexual 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 genitals.

Vertical transmission of the hepatitis B virus occurs mainly in regions with a high prevalence of virus carriage. The mother can infect the child if she is a carrier of the virus or has hepatitis in the last trimester of pregnancy. The child can become infected transplacentally, during childbirth or immediately after. Transplacental transmission occurs relatively rarely - no more than 5-10% of cases. However, the risk of infection increases sharply if HBeAg is detected in the mother's blood, especially in high concentrations.

Children become infected from mothers who are carriers of the hepatitis B virus mainly during childbirth due to contamination with blood-containing amniotic fluid through the macerated skin and mucous membranes of the child or during passage through the birth canal. In rare cases, the child becomes infected immediately after birth during close contact with the infected mother. In these cases, the infection is transmitted through microtrauma, i.e. parenterally, and possibly during breastfeeding. In this case, the child becomes infected not through the mother's milk, but parenterally due to the mother's blood getting onto the macerated mucous membrane of the child's mouth due to possible cracks in the nipples.

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

In recent years, the contact-household route of transmission of hepatitis B has become increasingly important. In essence, this is the same parenteral route of infection, since infection occurs as a result of virus-containing biological material (blood, etc.) getting onto damaged skin and mucous membranes. Transmission factors can include toothbrushes, toys, manicure accessories, razors, etc.

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

In adults, hepatitis B infection occurs through sexual intercourse (60-70%), injections of psychotropic substances, and various medical procedures.

Previously expressed assumptions about the existence of other routes of transmission of hepatitis B (waterborne, feco-oral, through blood-sucking insects) have not been confirmed at present.

Theoretically, it is possible to assume the possibility of transmission of the hepatitis B virus through insect bites (mosquitoes, midges, bedbugs, etc.). This transmission route has not been confirmed, despite the fact that some researchers have managed to detect markers of the hepatitis B virus in blood-sucking insects immediately after bloodsucking. However, given that the virus does not replicate in the body of blood-sucking insects, infection, if possible, is only possible at the moment of their crushing, that is, mechanically by rubbing virus-containing blood into 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 apparently universal, but the outcome of a person's encounter with the virus is often asymptomatic infection. The frequency of atypical forms cannot be accurately calculated, but judging by the detection of seropositive people, it can be said that for every case of manifest hepatitis B there are tens and even hundreds of subclinical forms.

It is believed that the prevalence of subclinical forms is associated with the leading role of natural routes of infection transmission, in which the infective dose is usually extremely small. The leading role of the infective dose may also be evidenced by the fact that, in the case of infection by blood transfusions, predominantly manifest forms of the disease develop, including almost all malignant ones, whereas in the case of perinatal infection and household contact, a chronic sluggish infection is formed.

High incidence of hepatitis B was registered in both adults and children in the late 90s of the 20th century. At the beginning of the 21st century, there is a sharp decrease in the incidence of hepatitis B in our country, which can be associated with the widespread implementation of vaccine prophylaxis.

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

According to Rospotrebnadzor, in 2007, Russia had a very high incidence of hepatitis B in children in their first year of life, amounting to 1.65 per 105 of this contingent and exceeding by 3.6 times the overall incidence rate in children (under 14 years of age), equal to 0.45 per 105 of the child population. This fact arose against the background of a sharp decrease in the incidence of hepatitis B in children from 1998 to 2007, from 10.6 to 0.45 per 105 of the population.

It should be emphasized, however, that in recent years, due to preventive measures (donor selection, reduction of indications for blood transfusions, general alertness), the incidence rate of hepatitis B in young children has been steadily decreasing. In 2000, the incidence rate in Russia in children under 2 years of age was 10.5, while in 1987 it was 27.3, and in 1986 it was 35.1.

According to research data, children in the first year of life are infected in 20% of cases during blood transfusions and blood components, in 10% - during parenteral manipulations, in 60% - during childbirth, and only in 10% of cases can antenatal infection be assumed. Presumably, the place of infection of children in 51.4% of cases was maternity hospitals and hospitals, in 16.3% - children's clinics.

Seasonal fluctuations in the incidence of hepatitis B are not typical. When infected as a result of preventive vaccinations, mass medical examinations, transfusion of infected blood or its preparations from one package to several children, several cases of hepatitis B may occur. In closed children's institutions and families, repeated cases may occur, which is usually associated with the long-term presence of the source of infection in the children's group and possible infection of new people through household means.

As a result of acute hepatitis B, stable lifelong immunity is formed. The occurrence of a repeated disease is unlikely.