After being instrumental in the eradication of smallpox, D A Henderson , director, Centre for Civilian Biodefence, Johns Hopkins University, USA, finds that changes in the environment are leading to mutations in viruses making them more dangerous. He talks to Vibha Varshney about the many new diseases emerging around the world
Why have we been witnessing so many different communicable diseases recently?
Increase in population has given rise to densely inhabited areas leading to poor sanitation. This gives perfect opportunities to microbes to spread. Along with this is the problem of malnutrition, which sometimes goes hand in hand with the increase in population making people susceptible to microbial infections. Also people travelling to different parts of the world carry infections with them. More and more people are venturing into hitherto unexplored areas and this has introduced new diseases to the human population. Hospitals are also instrumental in spreading diseases. Poor sanitary conditions, difficulty in imposing quarantine on patients and the high number of visitors, doctors and nurses who come in contact with the patient are a reason.
Can advances in medicine help?
Advances in medicine have created their own set of problems. A lot of antibiotics are used in hospitals. Therefore hospitals are also the areas from where antibiotic resistant microbes emerge. Change in food production has also increased the spread of diseases. Earlier, food was produced locally and consumed locally. But this is not the case now. We are actually trading in diseases along with food.
To what extent is ecological degradation responsible for the spread of disease?
This is one of the reasons and works along with and helps the process of mutation. In case of the Human Immunodeficiency Virus, the virus was carried by monkeys and most probably infected a small group of people near the forest. With the building of roads, more people moved out of the area and many more came in. This gave the virus a chance to change and become lethal. Let us take the case of China. Most mutant influenza viruses come from there. In this area a large number of pigs and fowl are present around people. This gives the organism a chance to mutate and jump from one host to another. Such a combination of hosts is not present anywhere else. The disease then moves to other areas.
How can we prepare to combat the threat of these diseases?
Considering the specialised knowledge and techniques needed to identify pathogens and contain them, it is better to have a centralised system. It should be connected to every city in every state. Links should be made to get information from the hospitals and the doctors who are actually attending to the patients. The people specialising in the subject (epidemic intelligence service) should be able to move immediately at a moment's notice. It is necessary that the specialists run tests for different pathogens at regular intervals to be able to recognise the disease when it actually occurs and not make mistakes in identification. For example, the disease that affected Surat last year was identified wrongly as plague. To avoid creating a panic, the authorities should make information available to all. There is also a necessity of having international collaborations as what India has today, some other country might have it tomorrow.
Several countries preserve pathogens of diseases that have been eradicated. Do you feel it is necessary considering that the microbes can be used by bioterrorists?
We have been able to eradicate only smallpox so far. In this case it is not necessary to maintain the culture, as it is not needed to prepare a vaccine. The vaccine is prepared from the cowpox virus and all cultures should be destroyed. Pathogens of all the other diseases are present in nature but the organisms needed to produce the disease are not there. For example breathing the anthrax bacterium is fatal but only 17 cases of pulmonary anthrax have been reported during the last 100 years and that also in people dealing with infected animals. The disease would be devastating if large numbers of spores are released in the environment.
How do we differentiate between a natural epidemic and the act of a bioterrorist?
We can tell this through carrying out epidemiological studies, which tell us about the origin of the microbe. In case it is localised and the source can be identified, it is natural but if the source cannot be identified; it is most likely to be the act of a bioterrorist. For example in case of foot-and-mouth disease, too much has happened too soon and the reason of its spread is not clear. Therefore, this might be the act of a terrorist.
How do we prepare to combat epidemics?
It is necessary to be alert and react quickly when the news of the epidemic comes. The personnel have to be ready 24 hours a day. We should be able to anticipate the problem and take timely action. Not having a good surveillance system is like not having a fire department. It is necessary that we are not complacent even about the diseases that have not been reported for a long time. Even if it is not fully controlled, the effect can be reduced.
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