Classification of Infectious Diseases

In the 19th century, infectious diseases were classed as contagious (transmissible from person to person), miasmatic (transmitted through air), and contagious-miasmatic. Late in the 19th century, in view of advances made in bacteriology, the diseases were classified according to their aetiology. These classifications could not satisfy clinicians or epidemiologists since diseases with different pat > *ciic-

sis, clinical course and epidemiologic characteristics were united in one group. Classifications based on clinical and epidemiologic signs proved ineffective too.

The classification proposed by Gromashevsky seems to be more reasonable than many others. It is based on the location of infection in the macroorganism. In accordance with the main sign, that determines the transmission mechanism, all infectious diseases are divided by the author into Jour groups: (1) intestinal infections; (2) respiratory infections; (3) blood infections; (4) skin infections. According to Gromashevsky, each group is subdivided into anthroponoses and zoonoses; their epidemiology and prevention differ substantially.

Intestinal infections. Intestinal infections are characterized by location of the causative agents in the intestine and their distribution in the environment with excrements. If the causative agent circulates in the blood (typhoid fever, paratyphoid A and B, leptospirosis, viral

Fig. 3. Transmission of intestinal infection (after Gromashevsky):

/-infected macroorganism; //-healthy macroorganism; /-excretion of, causative agent from an infected macroorganism; 2-life in the envi 3- entrance to a healthy macroorganism



hepatitis, brucellosis, etc.), it can also be withdrawn through various organs of the body, e. g. the kidneys, lungs, the mammary glands.

As a microbe is released into the environment with faeces, urine, vomitus (cholera), it can cause disease in a healthy person only after ingestion with food or water (Fig. 3). In other words, intestinal infections are characterized by the faecal-oral mechanism of transmission.

Maximum incidence of intestinal infections occurs usually during the warm seasons.

The anthroponoses include typhoid fever, paratyphoid, bacterial and amoebic dysentery, cholera, viral hepatitis A, poliomyelitis, helminthiasis (without the second host). The zoonoses include brucellosis, leptospirosis, salmonellosis, botulism, etc.

The main means of control of intestinal infection are sanitary measures that prevent possible transmission of the pathogenic microorganisms with food, water, insects, soiled hands, etc. Timely detection of the diseased and carriers, their removal from food catering and the like establishments is also very important.

Specific immunization is only of secondary importance in intestinal infections.

Respiratory infections. This group includes diseases whose causative agents parasitize on the respiratory mucosa and are liberated into the environment with droplets of sputum during sneezing, cough, loud talks, or noisy respiration.

People get infected when the microbes contained in sputum get on the mucosa of the upper airways (Fig. 4). If the causative agent is unstable in the environment, a person can only be infected by close contact with the sick or carrier (pertussis).

Pathogenic microorganisms causing some diseases can persist for a period of time in an enclosure where the sick is present. Infected particles of sputum or mucus can dry and be suspended in the air. Some diseases of this group can spread through contaminated linen, underwear, utensils, toys, etc.

Since susceptibility of people, and especially of children to respiratory infection is very high, and since the infection is easily transmitted from the diseased (or carriers) to healthy people, almost entire population of a given area usually gets infected, and some people can be infected several times. Some diseases of this group form a special subgroup of children's infections (diphtheria, scarlet fever, measles, pertussis, epidemic parotitis, chickenpox, rubella). A durable immunity is usually induced in children who sustained the diseases. The main measure to control respiratory infections is to

Transmission of air-borne infection (after Gromashevsky): /-infected macroorganism; II healthy macroorganism; 1 -excretion of the causative agent from an infected macroorganism; 2-life in the environment; ^-entrance of the causative agent to a healthy macroorganism

increase non-susceptibility of population, especially of children, by specific immunization.

It is important to timely reveal the sick and carriers, and also to break the mechanism of infection transmission: control of overcrowding, proper ventilation and isolation of enclosures, using UV-lamps, wearing masks, respirators, disinfection, and the like.

Blood infections. The diseases of this group are transmitted by blood-sucking insects, such as fleas, mosquitoes, ticks, etc., which bite people and introduce the pathogenic agent into the blood (Fig. 5).

Tick-borne encephalitis, Japanese B encephalitis and some other infections are characterized by natural nidality which is due to specific geographic, climatic, soil and other conditions of infectij transmission. The morbidity is the highest during the warm which coincides with the maximum activity of the trans ticks, mosquitoes, etc.

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