Dr. Carlos Sosa, Professor and Ex Dean, Faculty of Natural Sciences, Autonomous University of Queretaro, Mexico (carlosfranciscososa@gmail.com), May 2009.
Organisms that cause diseases, better known as pathogens, have evolved along with the organisms that host them, in a never ending race between adaptation and resistance. This competition or co-evolution has been altered by us humans, as we have changed the natural conditions in which this relationship has been developed. Among the causes of disease, outbreaks and their dispersion are: overcrowding, the disruption of the environment (like deforestation or watershed alteration), production and accumulation of pollutants, artificial selection of plants and animals, the misuse of pesticides and antibiotics, introduction of exotic plants or animals and other practices.
Although modern public health and epidemiology practices consider these factors, the control of diseases that have affected humanity for hundreds of years is far from being achieved, and new diseases keep appearing.
A valid question is: will sustainable agriculture and environment conservation help control the appearance and dispersion of diseases?
The answer will rest on the understanding of how intensive agricultural systems and environment make human populations more susceptible to infectious diseases, and on accepting that traditional medicine can provide cures to certain infections.
Artificial farm environments provide adequate conditions for some pathogens to cause infection. For example, conditions of temperature, humidity and ingestion of fecal matter causes coccidia infections in broilers, beef cattle and sheep under intensive (feed lot) conditions. Close contact between animals allows respiratory diseases to be transmitted. At the same time storing large quantities of feed stuffs, under these same systems, attracts rats, squirrels, birds and insects that can carry bacteria (like leptospira and listeria) and viruses that cause infections transmissible to humans. At the same time diseases that become endemic of farms (like tuberculosis, influenza and others) are transmitted to wild animals (like opposums or migratory birds) that will carry them to other locations. In some countries it has been found that viruses that cause blue tongue, swine fever, West Nile fever and others are not only been transmitted by wild animals but also are causing high mortality among them, or that it is needed to cull large numbers of individuals (like bats carrying rabies) in order to stop them from spreading the diseases even more. There are many examples of diseases introduced to the human population by disrupting natural habitats, such as the case of ebola, sars, aids and others.
Control measures for diseases or vectors, like use of antibiotics and pesticides in a large scale, has not only failed to stop outbreaks but has created resistant strains of bacteria and insects or ticks, thus making it more difficult to prevent or treat diseases that were supposed to be eliminated some time ago. Some countries have barred the use of antibiotics as food additives for livestock to avoid bacteria in becoming resistant to them.
Artificial selection of farm animals has resulted in individuals with efficient metabolism to convert food to meat, milk or eggs, but also in less genetic variation. The metabolic stress they endure makes them less resistant to infection diseases and parasites, thus the need for complex programs of vaccination and extensive use of disinfectants and antibiotics.
On the other hand extensive systems are not free themselves of diseases, mainly caused by parasites (internal and external) that have their natural cycles in the environment where animals are raised. These parasites may transmit infectious diseases to animals and to humans too. Some practices of grazing management may decrease the load of parasites and immunization programs may decrease the risk of infection. The culling of farm animals carrying infections is a practice that requires testing for positive reactors.
What can be done to stop this cycle of recurring diseases?
Many countries have in place plans to monitor animal populations for the control of outbreaks and to prevent them to be spread to humans. However, these plans have been more effective in controlling outbreaks in animals than in humans. Part of the reason for this failure is the lack of education of public and officials about the dangers of some practices associated to intensive production systems and the damage to the environment. Thus the first step to control and prevent epidemics is education.
It is essential to educate the public on the proper use of antibiotics. In some countries antibiotics are sold over the counter or used indiscriminately in farms or prescribed by Doctors to cure mild infections. Education is also needed to teach producers to change some agricultural practices to decrease the use of pesticides.
Research to rescue traditional knowledge on curative plants should be encouraged and should be financed by governments. These plants represent genetic resources that will help cure diseases that so far have not been controlled.
As an example on the effect of education and the use of traditional medicine is teaching people in malaria infested areas to use mosquito nets to prevent transmission of the protozoa (Plasmodium falciparum) and the use of the Wormwood plant (Artemisia annua) to treat those sick to avoid resistant strains. Similarly, the use of the neem tree (Azadiracta indica A. Juss) assists in controling parasites without the use of pesticides that may induce resistance.
A word of caution is that the cultivation of these plants should be promoted for local farms and the production of the extracts for local firms to make the cures more accessible and to promote sustainable growth. There is a risk that some companies may try to patent the extracts and then sell the products at a much higher price than if locally produced. Finally, in large cities it is required to educate public and officials on the importance of understanding and implementing ways to prevent the spread of transmissible diseases and to understand the true sources of disease to avoid panic or inadequate measures that may impose economic loses.