It is not easy to think of any social problems in the contemporary world that deserves greater attention than the foggy adversity of chronic and widespread undernutrition. ~ Amartya Sen

The recorded history of mankind demonstrates the close association between war, pestilence, famine and death. These are portrayed as the four Horsemen of the apocalypse in St John’s allegory. The four Horsemen in particular have presented the Christian world with a fearful sense of apocalyptic foreboding, in which the world will be struck by the horrors of war, famine, plague, and death before the Second Coming of Christ.

Fever, poverty and poor nutrition went together. Famines have been associated with outbreaks of such diseases as typhus, relapsing fever, smallpox and cholera. The tropical diseases, especially malaria, dysentery were mainly prevalent among the poverty stricken. However, poverty is also associated with inadequate shelter, overcrowding and insufficient sanitary services, which facilitate the passage of micro-organisms from person to person (cross infection). This happens when a disease spreads as an air-borne infection or by food or water, or transmitted by insects.

It appears that nutrition and infection form a two-way relationship. While nutrition is a prominent factor regulating the body’s defence mechanism against infection (immunity); infections are also known to affect the metabolism of nutrients and increase the state of malnutrition. Thus malnutrition and infection represent a vicious cycle and children are among the major victims. Our immune system has two facets ~ non-specific or innate, and specific which is acquired as a result of infection.

Most microorganisms encountered by us in our daily life are repelled before they cause detectable signs and symptoms of diseases. These potential pathogens, which include viruses, bacteria, fungi, protozoans, and worms, are quite diverse. Once pathogens enter our body, the innate immune system provides a kind of non-specific protection through a number of defence mechanisms, which include physical barriers such as the skin, and mucus membrane linings of the respiratory, gastrointestinal, and genitourinary tracts; mechanical systems like the cilia; reflexes like cough and sneezing; lysozyme in body fluids like tears, saliva, urine; bactericidal components present in some body fluids.

Normal healthy bacteria found in skin and inside our body also helps to suppress growth of pathogenic microbes. Some pathogenic microorganisms ~ bacteria or virus ~ that could penetrate the body’s first line of protective barrier, enter the internal tissues, where they encounter a chemical barrier which is composed of a variety of chemical substances that may prevent their growth. These include substances known as lysozyme, some proteins and certain kinds of white blood cells.

Lysozyme is an enzyme that kills the bacteria. There is a special kind of protein that disarms the bacteria by coating them. White blood cells known as phagocytes kill bacteria by engulfing them. Cells that have been infected with virus produce interferon, which send a signal to other cells of the body to resist viral growth. All these mechanisms are non-specific and mounted to the same extent with all types of infections. But they do not leave any memory as seen in acquired immunity.

There are two types of acquired immunity ~ humoral and cell-mediated. Humoral immunity is mediated through a class of protein called antibodies which are produced by a type of cells called B-lymphocytes (also called B-cell) in response to stimulus of foreign proteins in the invading organisms known as antigens. Antibodies so produced react specifically with antigens of the invader and destroy it. Under the stimulation lymphocyte gets activated to multiply into a large number of identical cells, called clone.

Each member of the clone carries the same antigen receptor and hence has the same antigen specificity as the original lymphocyte. So, for every antigen or foreign protein (in case of bacterial or viral infection) that enter our body, specific antibody is produced by a cluster of B-cells. Even after the infective episode, some of the B-cell specific for a given protein of the infective organism persists in the body. Hence, these are called memory cells. In case of another episode of the infection by the same organism these cluster of B-cells proliferate and mount the specific antibody response immediately. Indeed, acquired immunity is the basis of immunization.

If an animal or human being is injected with heat-killed bacteria or attenuated bacteria in small doses, antibody response can be produced and the memory imprinted. In the event of being attacked by a virulent form of the same bacteria or viruses the host is equipped with the fighting arsenal and can kill the culprit bacteria or virus by producing appropriate antibodies to that bacteria or virus. Malnutrition by itself can cause death.

However, epidemiological data also reveal that it increases susceptibility to and severity of infections. Among the nutritional disorders, the most common ones are protein-energy malnutrition (PEM), iron deficiency anemia, Vitamin A and B-complex and goiter due to iodine deficiency. Zinc deficiency has also been reported in some countries. Nutritional status also influences the duration of the asymptomatic phase between HIV infection and appearance of fullblown AIDS.

Iron deficiency anemia is one of the commonest nutritional disorders, with more than 50 per cent of the population, particularly pregnant women and children, in developing countries are suffering from it. Anemic children are more prone to infection, perhaps myeloperoxidase, an important enzyme for bacterial activity, is iron-dependent and its activity is affected in iron deficiency. Vitamin A deficiency is the major nutritional problem in most developing countries. The clinical manifestation of Vitamin A deficiency is night blindness.

Vitamin A is required for growth and cell differentiation, and its deficiency is known to compromise immunity. Infections such as diarrhoea and respiratory disease are frequently seen in children with Vitamin A deficiency. Covid-19 is the most contagious disease we have ever encountered. At the time of writing, the Covid-19 infected 41.5 + lakh in 187 countries/regions with deaths exceeding 284124.

The sharp rise in infections and deaths has caught many countries unprepared. The dexterity with which influenza viruses change their “coat proteins” can hamper the development of vaccines against them. The 2019-n-Cov, the virus causing Covid-19, not only emerged with an altogether unique coat but also a ‘cleverlydesigned’ genome that made it lethal. This has been unprecedented. As a result, no effective drugs or vaccines have yet been evolved to outwit this ‘intellectually superior’ virus.

Our immune system responds to such a virus with cytokines. Of course, the system should be strong enough so that the rate of production of cytokines becomes much higher than the rate of multiplication of the virus. By virtue of our immune system, some people will develop immunological resistance against such pathogens and thereby help to protect others of the community ~ a phenomenon called herd immunity.

In countries where malnutrition is common and often severe, the nutritional factor is of tremendous importance both in prevention and the treatment of infections. In the words of John Glenn: ‘If we could do something that enhances the body’s immune system here on Earth, it would be a tremendous step forward in the fight against the disease and cancer and other things.’

(The writer is a retired IAS officer)