Classification of communicable diseases
- In this section, communicable diseases are grouped into their main method of transmission, enabling
common control methods to be applied.
- The commonest causative organism is the virus, with arboviruses responsible for 118 diseases
which, with other organisms transmitted by mosquitoes, make this numerically the commonest cause
of infection.
- After vector control, hand washing and personal hygiene are the most important methods in the
prevention of communicable diseases.
1. Disease of poor hygiene
= poor hygiene is responsible for a number of diseases that include skin infections (scabies), eye
infections and tropical treponematoses (yaws, syphilis)
= arise from direct contact of the skin, conjunctiva of mucous membrane, or via intermediate vehicles
= conditions of poverty and large families, with the sharing of clothes, bedding and personal items, are
common factors
= flies, by their habits, are ready carriers of disease organisms, and specific control measures may
need to be undertaken to control them
= adequate quantities of water, with frequent washing, especially of the face where trachoma is
common, is the main control method
= long-term control is to provide water supplies with an adequate quantity of water. Good sanitation
should also be practiced
= trachoma (B)
2. Faecal-oral Diseases
= a large number of infections are transferred by faecally contaminated fingers, food or water =
transmitted by person-to-person contact, through water, food or directly to the mouth
= many of these infections produce diarrhoea, often adequately treated by oral rehydration solution.
Breaking the faecal-oral cycle is the basis of control by personal hygiene, increase of water supplies,
improvement in water quality, food hygiene and provision of safe sanitation
= vaccinations are available for the prevention of rotavirus, cholera, HepA and poliomyelitis
= gastroenteritis (V: rota, campylobacter, noro; B: e. coli)
= cholera (B), Hepatitis A (V), poliomyelitis (V: also airborne)
3. Food-borne Diseases
= the faecal-oral mechanism for transfer of infection often includes food as a mechanism of infections,
but some organisms can infect food in general (food poisoning) of be very specific in particular foods
in which the organism has a developmental cycle (helminth infections)
= where food poisoning is suspected, questioning of those involved in a relative risk assessment will
determine the likely cause
= there has been an increase in food-borne diseases due to the globalization and international
transportation of foods, particularly meat and poultry
= helminth diseases can nearly always be diagnosed by finding the specific egg in the faeces
= control is through food hygiene, the proper cooking of foods and sanitary methods to prevent the
food from being contaminated
= beef and tapeworms
4. Diseases of soil contact
, = several helminths require soil for the infective stage to develop, whereas the tetanus bacillus lives in
soil contaminated by animal excreta. Transmission can either by eating the soil, as a contaminant of
food or water (by swallowing nematode eggs), or by larval penetration of the skin when it comes in
contact with the soil (hookworms) of via a wound (tetanus)
= the promotion of personal hygiene and preventing contamination of soil through sanitation are the
main methods of control for the nematode infections
= hookworms (N: nematodes = roundworms)
5. Diseases of water contact
= infection with schistosomiasis is due to cercariae in water, which have developed in an intermediate
host snail, penetrating the exposed skin
= water becomes contaminated by faeces or urine, so effective sanitation, the reduction of snails and
preventing water contact are methods of control in schistosomiasis. The most effective method is
mass treatment, administering praziquantel to schoolchildren of selectively to those with serious
pathology
= schistosomiasis (H: helminth = parasitic worms)
6. Skin infections
= the skin is a common site for several communicable diseases, presenting with rashes of various
kinds. Infection is often transmitted from person to person directly by skin contact or by other means,
especially the airborne route by droplets or contact with contaminated surfaces and articles
= reduction in contact and personal hygiene are important
= control is by the avoidance of contact with infected individuals and, where available, the use of
vaccines: measles, mumps and rubella are all prevented by vaccination
= leprosy is a decreasing problem in the world as a result of active searching and well-managed
treatment regime
= measles (V: airborne), leprosy (B)
7. Respiratory Disease and other Airborne-transmitted infections
= infections of the respiratory system are the most important cause of morbidity and mortality in the
world. The vulnerable respiratory apparatus is easily invaded by microorganisms. The site of entry is
commonly the nasopharynx. The respiratory system also includes connections to the middle ear, the
sinuses and the gastrointestinal tract
= although numerous organisms are responsible for producing infection, it is the response of the host
that determines the severity of the disease
= the main method of transmission is by droplets, either coughed/sneezed directly on to another
person. Droplets are also sprayed onto surfaces for which they are inadvertently transferred to
mucous membranes (contact with these by hands and fingers can be just as important a method of
infection)
= tuberculosis (B), acute respiratory infections (V), influenza (V: also by contact)
= pertussis (whooping cough, B), diphtheria (B)
= meningococcal meningitis (B), haemophilus influenza (B), pneumococcal disease (B)
8. Diseases transmitted via body fluids
= a number of important infections are transmitted by the body fluids of blood, serum, semen, saliva
(speeksel) and various other discharges, and include the sexually transmitted diseases, HIV, hepatitis
viruses and haemorrhagic fevers
= these are the diseases of very close contact, direct from person-to-person with sexual transmission
accounting for the largest number of persons affected. These are, therefore, social diseases,
determined by the habits and attitudes of people, and it is only by effecting changes in these values
that any permanent improvement will occur
= sexual transmission is increased by contact with commercial sex workers and having multiple
partners, and then generally transferred to the spouse, also often affecting children
- In this section, communicable diseases are grouped into their main method of transmission, enabling
common control methods to be applied.
- The commonest causative organism is the virus, with arboviruses responsible for 118 diseases
which, with other organisms transmitted by mosquitoes, make this numerically the commonest cause
of infection.
- After vector control, hand washing and personal hygiene are the most important methods in the
prevention of communicable diseases.
1. Disease of poor hygiene
= poor hygiene is responsible for a number of diseases that include skin infections (scabies), eye
infections and tropical treponematoses (yaws, syphilis)
= arise from direct contact of the skin, conjunctiva of mucous membrane, or via intermediate vehicles
= conditions of poverty and large families, with the sharing of clothes, bedding and personal items, are
common factors
= flies, by their habits, are ready carriers of disease organisms, and specific control measures may
need to be undertaken to control them
= adequate quantities of water, with frequent washing, especially of the face where trachoma is
common, is the main control method
= long-term control is to provide water supplies with an adequate quantity of water. Good sanitation
should also be practiced
= trachoma (B)
2. Faecal-oral Diseases
= a large number of infections are transferred by faecally contaminated fingers, food or water =
transmitted by person-to-person contact, through water, food or directly to the mouth
= many of these infections produce diarrhoea, often adequately treated by oral rehydration solution.
Breaking the faecal-oral cycle is the basis of control by personal hygiene, increase of water supplies,
improvement in water quality, food hygiene and provision of safe sanitation
= vaccinations are available for the prevention of rotavirus, cholera, HepA and poliomyelitis
= gastroenteritis (V: rota, campylobacter, noro; B: e. coli)
= cholera (B), Hepatitis A (V), poliomyelitis (V: also airborne)
3. Food-borne Diseases
= the faecal-oral mechanism for transfer of infection often includes food as a mechanism of infections,
but some organisms can infect food in general (food poisoning) of be very specific in particular foods
in which the organism has a developmental cycle (helminth infections)
= where food poisoning is suspected, questioning of those involved in a relative risk assessment will
determine the likely cause
= there has been an increase in food-borne diseases due to the globalization and international
transportation of foods, particularly meat and poultry
= helminth diseases can nearly always be diagnosed by finding the specific egg in the faeces
= control is through food hygiene, the proper cooking of foods and sanitary methods to prevent the
food from being contaminated
= beef and tapeworms
4. Diseases of soil contact
, = several helminths require soil for the infective stage to develop, whereas the tetanus bacillus lives in
soil contaminated by animal excreta. Transmission can either by eating the soil, as a contaminant of
food or water (by swallowing nematode eggs), or by larval penetration of the skin when it comes in
contact with the soil (hookworms) of via a wound (tetanus)
= the promotion of personal hygiene and preventing contamination of soil through sanitation are the
main methods of control for the nematode infections
= hookworms (N: nematodes = roundworms)
5. Diseases of water contact
= infection with schistosomiasis is due to cercariae in water, which have developed in an intermediate
host snail, penetrating the exposed skin
= water becomes contaminated by faeces or urine, so effective sanitation, the reduction of snails and
preventing water contact are methods of control in schistosomiasis. The most effective method is
mass treatment, administering praziquantel to schoolchildren of selectively to those with serious
pathology
= schistosomiasis (H: helminth = parasitic worms)
6. Skin infections
= the skin is a common site for several communicable diseases, presenting with rashes of various
kinds. Infection is often transmitted from person to person directly by skin contact or by other means,
especially the airborne route by droplets or contact with contaminated surfaces and articles
= reduction in contact and personal hygiene are important
= control is by the avoidance of contact with infected individuals and, where available, the use of
vaccines: measles, mumps and rubella are all prevented by vaccination
= leprosy is a decreasing problem in the world as a result of active searching and well-managed
treatment regime
= measles (V: airborne), leprosy (B)
7. Respiratory Disease and other Airborne-transmitted infections
= infections of the respiratory system are the most important cause of morbidity and mortality in the
world. The vulnerable respiratory apparatus is easily invaded by microorganisms. The site of entry is
commonly the nasopharynx. The respiratory system also includes connections to the middle ear, the
sinuses and the gastrointestinal tract
= although numerous organisms are responsible for producing infection, it is the response of the host
that determines the severity of the disease
= the main method of transmission is by droplets, either coughed/sneezed directly on to another
person. Droplets are also sprayed onto surfaces for which they are inadvertently transferred to
mucous membranes (contact with these by hands and fingers can be just as important a method of
infection)
= tuberculosis (B), acute respiratory infections (V), influenza (V: also by contact)
= pertussis (whooping cough, B), diphtheria (B)
= meningococcal meningitis (B), haemophilus influenza (B), pneumococcal disease (B)
8. Diseases transmitted via body fluids
= a number of important infections are transmitted by the body fluids of blood, serum, semen, saliva
(speeksel) and various other discharges, and include the sexually transmitted diseases, HIV, hepatitis
viruses and haemorrhagic fevers
= these are the diseases of very close contact, direct from person-to-person with sexual transmission
accounting for the largest number of persons affected. These are, therefore, social diseases,
determined by the habits and attitudes of people, and it is only by effecting changes in these values
that any permanent improvement will occur
= sexual transmission is increased by contact with commercial sex workers and having multiple
partners, and then generally transferred to the spouse, also often affecting children
