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Risk Trade-Offs in Public Health Action: The West Nile Virus Example

I Introduction

It has now been two years since West Nile virus (WNV) was first detected in Canada. To some, the threat of WNV requires comprehensive control measures, including pesticide use to reduce mosquito populations that can transmit the virus to humans. Others, however, oppose pesticide use based on concerns that pesticide exposure may cause more harm to human and ecological health than WNV. These opposing views can be expressed with equal vigour, demonstrated by the fact that 25 individuals are suing the Ontario government for allegedly failing to do enough to protect the public from the disease while other groups are organizing anti-pesticide initiatives in their communities.

When threats to human health emerge, people understandably expect health officials to take action to protect them from harm. The challenge for officials is to determine the nature and degree of appropriate intervention, ethically and legally. In many cases, public health officials must weigh significant trade-offs in deciding how to act.

II Public Health Interventions

Choosing appropriate interventions involves considering the extent to which the community interest in protecting health justifies infringing individual freedom and autonomy.

The emergence of WNV in Canada is an example of a situation in which taking action to reduce one health risk may create another. Since mosquitoes are the vector of WNV, measures to reduce mosquito populations are one way to control the spread of the disease. Such measures include reducing the number of aquatic environments in which mosquitoes breed, application of pesticides to kill larval and adult mosquitoes, release of predators such as fish that consume larvae and dragonflies that feed on adults, and deployment of mosquito-trapping devices. Of these measures, pesticide use (especially adulticides, which are sprayed aerially) often generates the most controversy due to concerns about the effect of chemical exposure for humans, other organisms, and the environment.

Implementation of these measures varies greatly in the degree of intrusion into the lives of individuals. Public education campaigns that advise individuals how to minimize mosquito breeding environments on their property and avoid being bitten are minimally intrusive public health interventions. A more aggressive intervention may occur if officials levy fines against individuals who create health hazards such as mosquito breeding sites on their property. Arguably the most intrusive intervention may occur when public health officials spray pesticides in communities to kill adult mosquitoes.

In some situations, interventions may pit individual interests, such as non-interference with person and property, against a broader public-health interest in using some degree of interference in order to safeguard conditions for health in communities. Public health officials must always be concerned with whether interventions can be justified, both ethically and legally.

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III Public Health Laws

Public health laws throughout Canada empower officials to act to combat threats to health, including infectious diseases. In addition to public health laws, Canadian provinces generally have laws that permit government authorities to declare states of emergency based on natural disasters or other events that constitute serious threats to public health and safety. In some circumstances, officials may believe it necessary to use emergency power to authorize action against the risk posed by a health threat like WNV.

For example, in May 2002, the Province of Manitoba amended its Environment Act to authorize the Environment Minster to order municipalities to take steps to alleviate public health emergencies. Following this amendment, the Manitoba Minister of Health declared that West Nile virus posed an imminent health emergency and ordered the City of Winnipeg to undertake additional pesticide application measures. In addition to expanding the pesticide spray program in Winnipeg, this order also rescinded a buffer zone provision that had allowed residents to advise the City not to spray within 100 metres of their property.

Similarly, the Quebec government passed a bill in June 2001 to permit aerial spraying of pesticides to combat West Nile virus. This legislation overrode other legislation, including municipal bans on pesticide use, and exempted the government from environmental regulations that normally require permits for aerial spraying of pesticides.

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IV Public Protest

These types of emergency actions, although based on legislative authority, are not without controversy. Government officials who consider invasive public health interventions must consider not just whether they have legal authority to do so but also the real possibility that such action will be challenged. Such challenges may include lawsuits to prevent pesticide spraying, outspoken public opposition through media, or civil disobedience aimed at impeding spray initiatives. Indeed, one commentator has remarked that "[i]n a modern society, public health initiatives, no matter how justified and necessary, are likely to be scrutinized and challenged, both in the media and in the courts." (1)

In response to the Manitoba government's decision to declare a health emergency and order the City of Winnipeg to expand its pesticide application program, city residents took to forms of civil disobedience to protest the action. As the National Post reported in July 2002, "Residents of a normally quiet Winnipeg neighbourhood blockaded their street for two nights this weekend in a bid to keep out pesticide-spraying trucks the city has dispatched to kill off mosquitoes headed west across the country carrying the West Nile virus with them. A dozen residents lined up cars and dumpsters at the end of their street on Friday night, then camped out in tents on Sunday night, forcing fogging trucks to bypass their residential neighbourhood community." (2)

Some Quebec residents also objected to that province's decision to enact override legislation to authorize pesticide spray programs against West Nile virus. Although the provincial epidemiologist in Quebec was reported as saying the government would only use aerial spray as a last resort, a group comprised largely of physicians and scientists, known as the Coalition for Alternative to Pesticides, launched an open-letter campaign criticizing the government's action.

In addition to these forms of protest, government health officials who proceed with pesticide spraying may face legal action. For example, after New York City announced it would conduct aerial spraying of mosquitoes, a group of environmental organizations launched a court challenge to stop the spray program. In another lawsuit, representatives of the lobster industry in New York and Connecticut alleged that pesticides applied aerially to combat West Nile virus washed into Long Island Sound and killed millions of lobsters. Industry representatives filed a $125 million class action claim against manufacturers of the pesticides used to spray for the mosquitoes.

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V Conclusion

While WNV may cause serious harm for a small number of individuals who are infected, pesticide exposure may result in harms to others. An even more challenging situation for public health arises when the risk trade-off between two harms is unpredictable or largely equal. Before acting in such situations, government bodies and public health officials must carefully weigh available evidence about the harms and efficacy of various courses of action and pursue less intrusive action first to determine if it will reduce the target health risk while avoiding the creation or exacerbation of other risks.

As these examples demonstrate, health officials must also be prepared to respond to opposition to controversial public health measures. The threat of challenge is probably most likely in situations where citizens feel they have not been properly consulted or warned of action or where they perceive that the risk trade-off is simply too high. Further, when governments turn to emergency powers to authorize intrusive public health interventions, citizens may feel they must speak out or use legal action to safeguard their interests. Careful evaluation of risks, adequate public education, as well as appropriate selection of minimally intrusive interventions, are optimal courses of action.

VI References

(1) Wilfredo Lopez, "West Nile Virus in New York City," (2002) 92, American Journal of Public Health 1218 at 1219.

(2) Jon Bricker, "Pesticide trucks blocked from Winnipeg street," National Post (22 July 2002), A6.