DEBATE/DEBATE

Debate sobre o artigo de Castiel

Debate on the paper by Castiel

Francis L. Black

Department of Epidemiology and Public Health; Yale University School of Medicine

This paper touches a responsive chord. I give a compulsory course to Public Health students with the purpose of teaching them not to be afraid of molecular biology. I am concerned, however, that Castiel has not always distinguished between private and public health.

Public Health is in a crisis brought about by increased population densities and the lack of funding. Prevention does not attract the attention that the great therapeutic advances of recent decades get. Many of the spectacular therapeutic advances derive from the new understanding of Molecular Biology, a body of knowledge often ignored by practitioners of Public Health. Castiel is right that reversal of this omission would do much to help Public Health, but let us make sure we use it for the public and not just to improve prospects for individuals.

The paper touches on the role of PCR (polymerase chain reaction) in the detection of occult pathogens, but does not get as far describing the role of pathogenic sequence determination in defining the relatedness of multiple isolates and the routes by which specific lineages have spread. These methods have had particular relevance in the end stages of poliomyelitis control. Recent isolates from Brazil derive from vaccine strains and hence pose little risk to the populance. In Canada, however, isolates have been related to pathogenic Dutch strains. This molecular similarity revealed a hole in the Hemispheric defense against poliovirus through which virus was brought by members of a religious sect that eschewed medical care and had branches in Holland and Canada.

Castiel emphasizes the role Molecular Biology has had in human genetics and the contributions that this made to our understanding of differential diseasesusceptibility. An emphasis is placed on how genetics may affect interaction with environmental insults and hence predict differential risk from the same environmental hazard. I am concerned that, while this aspect is clearly applicable to individual risk, it is difficult to apply to public risk.

The challenge to epidemiologists to develop causal theories utilizing new knowledge of genetic and epi-genetic effects is real, but it is not enough to use the findings to measure risks faced by individuals. We must be able to apply it to defined populations, but we cannot in test whole populations for a battery of genetic defects; the cost is too great. Groups with similar risk must be defined and representative samples tested. Castiel might tell Joao that he can smoke up to a pack of cigarettes a day without great risk of developing lung cancer and Pedro that he must avoid tobacco smoke wherever possible because he has a defective p53 gene. There would be the problems Castiel has recognized in getting Joao and Pedro to perceive the risks realistically ans act appropriately, but my chief concern is different. This would be good preventive medicine, and good etiology, but it would not be Public Health.

There are some genetic diseases, associated with specific populations, that could be reduced by public health methods. One example is the "New World Syndrome" first defined by James Neel. This consists of a triad of obesity, diabetes and cholelithiasis prevalent in populations that have traditionally lived in alternating feast and famine. When ample food is available their insulin levels encourage packing the calories away as fatty reserves. A countervailing reduction of appetite is not elicited until much damage is done. Groups subject to this propensity could be defined without individual tests and educational programs and intensified surveillance instituted.

Ethical concerns apply as much here as to individual risk and such knowledge will have to be managed with the greatest care. Long ago it was noted that North American Indians become inebriated more easily than Caucasians because, we now know, they metabolize ethanol more slowly. The solution was to ban the sale of alcoholic beverages to any Indian. The effect was that alcohol became a forbidden pleasure to be indulged in without restraint whenever the occasion presented. Discrimination in this case caused the law to backfire and drunkenness may actually have increased.

Yes, let us as public health workers exploit the opportunities presented by molecular biology. Let's use them to identify pathogens and to determine machanisms behind genetically determined risks, so we can better determine what should be avoided. But let us never forget that our special charge is to the public. We must leave to others the elaborate methodologies that serve only the individual.