Haemophilus influenzae type B – symptoms and vaccine

Haemophilus influenzae are gram-negative short rods whose name (Greek: Hemal – blood, philos – friendly) is related to specific growth requirements. In bacteriological media, the presence of erythrocytes is necessary, as they supply the factors important for growth – hematin and nicotinamide adenosine diphosphate (NAD). This bacterium was first described in 1883 by Robert Koch, who isolated it from pus from a patient with conjunctivitis. In 1893, Pfeiffer decided that Haemophilus influenzae is the etiological factor of influenza and that the name of the species includes the word influenza.

Haemophilus influenzae – clinical division

Haemophilus influenzae a grypa

The viral etiology of influenza was not discovered until 1933. Haemophilus influenzae sticks occupy an important place in human pathology and are responsible for infections with a varied clinical picture. The division of these bacteria is based on the antigenic properties of the cell envelope. Some types of these rods contain a polysaccharide shell. Depending on the antigen contained in the shell of Haemophilus influenzae.

Haemophilus influenzae – epidemiology

Haemophilus influenzae are found only in humans. The natural habitat of these bacteria is the upper respiratory tract. About 40-80% of unvaccinated children and adults are healthy carriers of these bacteria, which in unfavorable circumstances for the host:

1. temporary weakening of immunity,
2. viral infection paving the way for secondary bacterial infection,

they can cause diseases of the respiratory tract, conjunctiva, less often bacteremia, meningitis, sepsis of the newborn.

Haemophilus influenzae – Child carrier

The capsular type b occurs primarily in young children. About 2-4% of them are carriers of these sticks (colonization in the throat or nose). The prevalence of Hib carriage in children varies widely from country to country. Preventive vaccination against this type and the percentage of immunized young children in the population are of decisive importance. The experience of many countries (including Finland) shows that after the introduction of mass vaccination against Hib, approximately 4 years later, the carrier of these microorganisms in the respiratory tract of healthy children disappears.

In unvaccinated populations, both carriage and b-type infections are most common in children 6-24 months of age, with rates declining and disappearing by the age of 5 years. Such age distribution of carriers and patients is conditioned by immunological mechanisms. Anti-type b resistance is dependent on the presence of antibodies against the polysaccharide antigens of the bacterial envelope. Antigens of this type, belonging to the so-called non-dependent thymus, do not stimulate the development of permanent immunity in children under 2 years of age, even after severe infection.

The youngest infants, up to the age of 6 months, are protected by maternal antibodies, passed on to the baby in the last weeks of pregnancy. Therefore, infections and carriers are less common in this age group. From the second half of their life up to the age of 2, unvaccinated children are not protected and therefore at this age the number of infections and carriers is the highest. After the age of 2, children gradually acquire the ability to produce antibodies to thymic-independent antigens and, as a result of natural contact with this microorganism, their immunity increases, which results in a declining number of carriers and less frequent infections.

How does Haemophilus influenzae infection occur?

Haemophilus influenzae is transmitted mainly to by the droplet path, it is favored by close interpersonal contacts. Therefore, infections are more common in communities – the phenomenon of carriage and infection is increasing among children attending nurseries and kindergartens, as well as in families with many children, especially those living in overcrowded apartments.

The epidemiological analysis of Hib infections is based on the clinically relevant division of these infections into:

1. invasive,
2. non-invasive.

Invasive infections include those cases in which bacteria are isolated from sterile sites in healthy people, i.e. blood, cerebrospinal fluid, peritoneum, pleura and pericardium.

Causes of Haemophilus influenzae infection

The factors that predispose children to invasive infections include:

• sickle cell anemia;

• anatomical or functional asplenia;

• HIV infection;

• some immunodeficiency syndromes;

• malignant tumors.

Invasive infections due to Haemophilus influenzae have also been reported to occur more frequently:

1. in boys,
2. in people of the black race,
3. indigenous people of Alaska,
4. Indians of the Apache and Navajo tribes,
5. in children attending nurseries and kindergartens,
6. infants who are not breastfed.

In countries where general vaccination against Haemophilus influenzae type b has been introduced, invasive infections are mainly observed in unvaccinated children or until primary vaccination is completed. Haemophilus influenzae type b infection remains an important and common pathogen responsible for a significant percentage of the death of young children in developing countries where no universal vaccination against this organism has been introduced.

Infection with Haemophilus influenzae in Poland

In Poland, registration of invasive infections caused by Haemophilus influenzae (all types, without distinguishing type b) was introduced only in 2005, in which 17 sepsis of this etiology were recorded. Previously, only purulent meningitis was recorded. In 2004, there were 77 such cases, in 2005 – 59, and in 2006 – 53. When analyzing these data, it should be borne in mind that the actual number of invasive infections caused by Haemophilus influenzae in Poland may be higher, as only about 30 In% of cases of purulent meningitis, an etiological factor is identified, and the frequency of blood cultures in young children with fever is low.

Haemophilus influenzae – vaccine

In April 2007, universal vaccination against this organism was introduced for infants. Epidemiological data from recent years indicate a decrease in the number of registered cases (2009 – 19, 2010 – 26), although it should be remembered that they may include infections caused by other types (not only b), and that some cases may not be identified in terms of etiology.

Source: J. Cianciara, J. Juszczyk, Infectious and parasitic diseases; Czelej Publishing House