After many natural disasters, famines and epidemics quickly follow with depressing predictability. It is not just a coincidence related to the damaged infrastructure and loss of stored foodstuffs. It has long been thought that there is a direct link between malnutrition and immune suppression, but the mechanism has been, and is still, poorly understood. It doesn’t take a natural disaster to cause the level of malnutrition necessary to trigger immune suppression. In 2005 malnutrition was considered contributing factor in half (53%) of all infectious disease deaths in children under five in the developing world. There is a growing recognition that the malnutrition-infection relationship is a factor in the quantity and quality of life in the elderly and chronically ill globally.
Malnutrition and infection can form a vicious cycle that can be hard to break. Malnutrition weakens both the innate (non-specific) and adaptive (specific) immune system making people more vulnerable to infectious diseases. The immune suppression can become so bad that they are as vulnerable as people with full-blown, uncontrolled AIDS. Because of the similarly between the malnourished immune system and AIDS, it is sometimes called “nutritionally acquired immunodeficiency syndrome” . The acute risk of immune suppression is increased vulnerability to infection. Not only do malnourished people contract common diseases at a higher rate, they also contract the rare infections that are typically only found in severely immune compromised people.
Large epidemics (or pandemics) bring society to a stand still. A large number of people are too ill to work or die preventing the most productive members of society from working. Care for ill people and orphans become a drain on community resources. Historically, few infants who have not been weaned survived the death of their mother. The lost productivity lowers food production and distribution deepening the malnutrition, setting up a repeat of the cycle until the community is uttered devastated and depopulated.
Malnutrition does not have to begin the cycle. Throughout history there have been laments over ripe fields that were left to rot because there were not enough healthy people to harvest the fields. Further the demands of the infection can cause or deepen malnutrition: diarrheal agents cause dehydration, and intestinal parasites and chronic infections like tuberculosis and malaria drain nutrients and can cause anemia. A Nigerian study found evidence that acute measles can measurably deepen childhood malnutrition .
Today this cycle can be mitigated and eventually broken by international food relief and even limited modern medical treatment. Intravenous hydration, basic antibiotics and vaccines regularly save the lives of thousands in nearly yearly famine related epidemics. International relief is a relatively modern phenomenon.
Indications of Immune Dysfunction
Evidence for the mechanism of immune dysfunction in malnutrition has been slow in coming. Much of the evidence has been observational: the frequency of rare infections like Pneumocystis carinii, and opportunistic infections like Noma . Malnourished populations have a higher incidence of chronic infectious diseases like tuberculosis and malaria.
Ominously, there is evidence that childhood malnutrition can cripple the immune system for life. Malnutrition directly correlates with atrophy of the thymus and consequently reduction in circulating T lymphocytes . Damage to the thymus correlates with increased circulating undifferentiated lymphocytes, poorly developed peripheral lymph nodes and spleen, and a dysfunctional mucus membrane immune response including poor IgA secretion. Protein synthesis is either insufficient or ineffective throughout the immune system. They lack cytokines and proper cell markers, have abnormal antibody responses and under-produce or lack complement proteins hampering phagocytosis . Some of this can be repaired with restoration of proper nutrition, but not all of it, especially damage to the development of the immune system infrastructure.
All of the abnormalities of the malnourished immune system are too complex to detail in this post. I hope to divide this topic up into multiple posts. The relationship between malnutrition and epidemics will be a returning theme here for the next six months or so. Suggestions on reading material to correlate depth of malnutrition with osteological analysis would be appreciated.
 Schaible UE, & Kaufmann SH (2007). Malnutrition and infection: complex mechanisms and global impacts. PLoS medicine, 4 (5) PMID: 17472433