Measles and models

Although measles is a mild disease for most people, it can result in severe complications and death. The Expanded Program on^lmmunization (EPI) of the World Health Organization (WHO) estimates that each year approximately 1.5 million children die of measles around the world. Pneumonia and diarrhoea cause most of the deaths, but other important complications include bronchitis, croup laryngitis, otitis, stomatitis, proteinlosing enteropathy, deafness and blindness. In developing countries up to 10% of infected children often die acutely with the highest death-to-case ratio occurring in infants. In those who survive recovery is slow. Affected children have marked weight loss from diarrhoea and the inability to eat or drink because of severe stomatitis and general malaise. Catch-up weight gain can take longer than three months, and the ilness can precipitate marasmus or kwashiorkor in those whose nutritional status is marginal at the onset of infection. Severely malnourished children suffer more complications and are more likely to die. Even in the developed world, the health impact of measles can be substantial. Between 1970 and 1975 there was an average of 6000 hospitalizations in the United States for measles annually. In Denmark, approximately 9% of cases developed otitis, 7% respiratory complications and 0.3% encephalitis.

Because the essential epidemiological characteristics of measles are well known and clearly defined, measles has been of continuing interest to epidemic theorists. Live attenuated measles virus vaccine

was introduced in 1963 and its ability to provide protection in a high proportion of those vaccinated was rapidly demonstrated. The first successful measles elimination programme started in 1966 as part of a programme of smallpox eradication and measles control in 21 countries of West and Central Africa and provided a useful opportunity to merge theoretical and implementation considerations. From surveillance data generated in Africa the late professor George McDonald developed mathematical models simulating the transmission of measles. His models suggested two approaches that might interrupt measles transmission in West Africa: Annual mass vacci­nation reaching at least 90% of susceptible children: or, an ongoing programme in which 75% of all susceptible children were vaccinated as they became susceptible at approximately six months of age. Absence of the necessary infrastructure necessitated the choice of mass campaigns. Using this approach, measles transmission was interrupted for varying periods: in the Gambia, a zero incidence of indigenous measles was achieved and maintained for more than two years.

Mathematical models also played a role in the measles elimination programme which began in the US in 1966. No precise estimate was made of the immunization levels needed to interrupt transmission, the effort in the US focused on achieving high immunity levels through the routine immunization of infants at one year of age and of immunizing at school entry children not previously immunized. However, in 1966 funding was directed to the development of programmes to prevent .rubella and as a result the effort was incomplete.

COMMON COLD

Common cold is an acute inflammation of the upper respiratory tract involving the nose and throat. It is one of the most familiar ailments which afflict mankind. Susceptibility to colds is almost universal, particularly among children. The cold is highly contagious, especially indoors, and places where groups of people congregate are excellent trtransmission spots for the infection.

In large urban communities where the climate is temperate the general population averages about three colds a year. This median is higher among susceptible adults and children. The incidence is lowest in the summer, rises in the autumn, reaching its peak in midwinter and declines in the spring.

Colds are definitely communicable and are transmitted either by direct contact or by spread of the infected droplets of discharge. The common cold is due to one or more viruses. When the cold virus attacks the mucous membranes of the nose and throat, these tissues are weakened and become susceptible to infection by bacteria which are also generally found in the body. The bacteria are secondary invaders and the virus paves the way for their entry into the mucous membranes. Although they are not responsible for the common cold, the bacteria may initiate a secondary infection which either intensifies the local inflammation present, prolonging the cold, or causes new complications such as purulent sinusitis or otitis, an inflammation of the ear. Infants and young children appear to be more susceptible to these secondary infections than adults.

A cold usually begins abruptly , with a sense of soreness and dryness in the nose or back of the throat. Within a few hours the nasal passages feel congested, sneezing develops and a clourless watery discharge comes from the nose. After fourty eight hours the cold is usually at its peak, and is accompanied by excessive watering of the eyes, huskiness of the voice, and difficulty in breathing as the congestion spreads. Frequently a headache, a sense of lethargy and malaise, and vague pains in the back and limbs accompany a cold. A fever is rarely present, although in children a temperature of 38.9 C or even higher often develops.

The uncomplicated cold generally lasts from one to two weeks and terminates without special treatment. The latter is confined to relief of symptoms and control of complications. Bed rest should be enforced whenever possible and as much isolation as is practical. Plenty of fluids, a light diet, and keeping warm promote greater comfort. Aspirin in small repeated doses generally gives relief as does gargling in cases of sore throat.

Measures must be taken to ward off the infection and decrease its incidence. A well-balanced diet, sufficient rest, proper dress both indoors and out, all help to keep the body resistance high. Undue exposure to sharp changes in temperature should be avoided. Proper ventilation of rooms, with sufficient humidity in the air, helps to keep the mucous membranes in healthy condition. Particular care should be taken to avoid contact with persons who have colds. Simple hygienic measures like washing the hands before eating or covering a sneeze all help to decrease the occurrance