Epidemiology of cholera

Pathogen survival in the environment

To understand the epidemiology of cholera, it is critically important to know the factors influencing the microorganism's survival. The pathogen demonstrates high sensitivity to a range of physical and chemical agents. Specifically, it is rapidly killed by:

• exposure to ultraviolet radiation;
• desiccation;
• heating (thermal processing);
• exposure to an acidic environment (low pH levels are lethal to the bacterium).

Most standard disinfectants effectively destroy the vibrio. However, there is an important epidemiological exception: the microorganism exhibits marked resistance to quaternary amine-based preparations, which must be taken into account when implementing sanitary and anti-epidemic measures.

Sources of infection and reservoirs

Cholera belongs to mixed-type infections known as anthroponoses-sapronoses. This means that the pathogen is capable of maintaining its circulation both within the human population and in the environment. There are three main categories of sources of infection:

1. The sick person (sheds the pathogen in huge quantities with feces and vomit).
2. Bacterially colonized individuals / carriers (people without clinical manifestations who actively shed the pathogen).
3. The aquatic environment and aquatic organisms (a natural reservoir ensuring the long-term persistence of bacteria outside the human body).

Comparison of biotypes: Classical and El Tor

The epidemiological picture of the disease changed dramatically with the shift in the dominant causative agent. The El Tor biotype possesses a number of evolutionary advantages over the classical variant:

• Scale of carriage: When infected with the El Tor biotype, asymptomatic carriage is significantly more common. Statistics show that for every clinically apparent case, there may be 10 to 1,000 hidden bacterial carriers.
• Environmental survival: El Tor is much more stable in the external environment. It is capable of entering into symbiosis with algae and other aquatic organisms.
• Adaptation: Upon the onset of unfavorable conditions, this biotype does not die, but rather transitions into so-called non-culturable forms while retaining its pathogenic potential.

Historical background and pandemic chronology

The historical and main endemic focus of cholera is the mouths of the Indian rivers Ganges and Brahmaputra. Until the 19th century, the infection was strictly local in nature and did not extend beyond this Asian region.

Global spread began in 1817, when the disease penetrated into Europe and America. Chronologically, the pandemics are divided into two major stages:

• 1817–1926: During this period, six pandemics swept across the world. All of them were caused by the classical biotype.
• From 1961 to the present: The seventh pandemic is ongoing. Its main culprit is the El Tor biotype.

Modern changes and the O139 Bengal strain

The evolution of the pathogen continues. In 1992, a new strain emerged in Bangladesh — V. cholerae O139 Bengal.

By its nature, this microorganism is a genetic derivative of the El Tor strain. Its main distinguishing feature is a modified antigenic structure. The emergence of the O139 Bengal strain provoked a major new epidemic that spread beyond the primary focus to other countries. During this process, sporadic cases of importation and infection with this strain were also registered within the Russian Federation.

Briefly: answers to topical questions

What else to study on this topic

• Mechanisms of bacterial transition into non-culturable forms
• Features of the symbiosis of vibrios with algae and aquatic organisms
• Genetic basis of antigenic structure changes in the O139 Bengal strain
• Causes of Vibrio cholerae resistance to quaternary amines
• Features of epidemiological surveillance for anthroponotic-sapronotic infections

Other topics in the section "Gram-negative facultatively anaerobic rods (Enterobacteriaceae, Vibrio, Haemophilus, Pasteurella)"

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