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since April 1998
CHOLERA - 1 Oct 98 There are currently - almost inevitably - large numbers of cholera cases in Dhaka, particularly in children. Cholera is endemic - that is continually present - in Bengal, and all the seven pandemics - world wide spreads - of the last two centuries probably originated here in this delta. The cholera organism Vibrio cholerae may actually prefer the presence of sea water and thus Bangladesh represents an ideal environment for it.
Vibrio cholerae is exclusively a pathogen of humans where it lives in the small bowel, producing a toxin which leads to profuse production of liquid. In severe cases, watery stools pour out of the body. Some of you may have seen "cholera beds" with a hole in the centre through which the stool passes straight into a bucket! It may actually look more like water with some mucus rather than faecal material and is traditionally called "rice water stools." Huge quantities can be produced, sometimes more than the total body weight of the patient and clearly, in severe cases, death may be rapid if fluid replacement is inadequate.
In the past, fluid was usually replaced intravenously. However one of the greatest and simplest medical advances of this century, the development of Oral Rehydration Solution, was made here in the ICCDR,B about 30 years ago. It was found that, whilst in cholera an oral solution of salt was not absorbed alone, it was absorbed rapidly and effectively if glucose was added. Further refinement has occurred including the discovery that powdered rice works as well or better than glucose alone. This has led to an easy, cheap method of replacing fluid loss which does not need any medical expertise. It works in all diarrhoeal diseases and has saved many millions of lives. It seems almost too obvious and simple.
Cholera is spread by water and faecally contaminated food stuffs. It is very easily killed by boiling and by stomach acid. Large numbers of organisms have to be taken in to get beyond the stomach and cause infection. Moreover the great majority of cases are mild and not life threatening. It is also extremely sensitive to several antibiotics.
Cholera is therefore a disease of the deprived without access to clean water and, as the mortality with simple medical treatment is extremely low, most deaths occurr where help is not available or sought too late.
The old vaccine was given intramuscularly, but the organism only lives in the lumen of the gut, almost inaccessible to any antibodies produced in the body. The vaccine plays no part in cholera control. Work on oral vaccines which would give cellular immunity in the bowel wall is underway. However the mainstay of prevention is careful hygiene and clean water supplies.
MEDICAL RISKS OF THE FLOODING - 13 Sep 98It is sad to be arriving at a time of yet a further natural disaster in Bangladesh. The floods have already led to a sharp increase in waterborne diseases. These particularly affect the depnved section of the population whose access to clean water is limited at the best of times and for whom boiling and cooking must now be impossible.
Even if we get, as is quite possible, a major epidemic of cholera or typhoid, sensible behavior will almost completely protect you. There are three main groups of waterborne pathogens, all of which respond to boiling:
VirusesThe Hepatitis A (HVA) and Hepatitis E (HVE) viruses are both spread by faecal contamination of water. Although HVA is mildly heat resistant, needing five minutes boiling to kill it reliably, there is an extremely safe effective vaccine which all adults should have had. As the disease is usually much milder in children (the younger the child, the more trivial the illness), they are sometimes ignored. However I would give the vaccine to all children over one year, giving priority with our stocks to older children. Check your immunisations: Some of you will know you are immune from Hepatitis A infection in the past. The vaccine was introduced in 1992 and probably lasts for ten years and so those of you who have been given it can relax. Any of you who are not immune, should come promptly. This is to my mind the most important vaccine for anyone visiting or living in South Asia.
HVE is relatively newly recognised and I cannot find firm information on its response to heat but the resistance of HVA is unusual and it is highly likely that it is rapidly killed by boiling. There is no vaccine. Hepatitis E is an unpleasant but relatively trivial illness for most of us, but is serious in pregnant women in whom the immune system is depressed. At times like this any of you who are pregnant should be especially careful, particularly avoiding salads.
BacteriaThis group includes Salmonella (such as the typhoid and paratyphoid pathogens), Shigella, the cholera organism and an important group, especially in children, known as the pathogenic E. coil. These are highly heat sensitive and are all killed below I OO degrees C. Therefore bringing water to a rolling boil briefly reliably eliminates risk. Besides, the risk from many bacteria, especially salmonella and cholera, is dose related as the immune system and stomach acid of fit adults will easily eliminate small numbers of organisms. (For this reason, it is often safe to wash your teeth in tap water which you would not otherwise consider drinking - but during the floods, you should use boiled water.) The risk is greater in the very young, the very old and, to a lesser extent, pregnant women as their immune systems are either underdeveloped or impaired.
Having said that, typhoid is very uncommon in small children as they are so carefully looked after. Those of you who are currently breast feeding should not be thinking of giving up at the moment as breast feeding also gives very considerable protection from gastro-enteritis.
Incidentally the typhoid immunisations - there are currently three types on the market -are only partially protective but worthwhile. The cholera vaccine is almost useless and we no longer stock it.
ParasitesOf these Giardia is quite the commonest in Bangladesh: Amoebae are much less so. Some worm ova are also spread by water. Although killed by boiling, like the other pathogens, they are extremely effectively removed by filtration and this gives added security.
Therefore: Have a system in your kitchen and observe all the regular sensible measures, - provide soap and a naubrush for all staff and see that they are used etc. Be a presence in your kitchen.
It probably does not matter whether the boiling or filtering is done first but it should always be done in the same order.
Susceptibility to gastro-enteritis varies widely. Those of you who have frequent problems need to be more careful. If you are worried, come and talk about it. I am particularly keen to meet you all - and am passionately interested in diarrhoea! Finally, in the long term, I would expect the floods to lead to an increase in mosquitos and this might alter what is at present a very low risk of malaria in Dhaka.