Disease Eradication

Lack of Nonhuman Reservoir

The presence of a pathogen in nonhuman reservoirs, such as soil or animals, reduces the likelihood of eradication. For instance, while the rabies virus in humans can be contained through either a preventive vaccine or postexposure treatment, wild animals such as bats or raccoons can introduce the virus into human populations. Mass vaccination of animals and other attempts at controlling all natural reservoirs of rabies are not globally feasible, ensuring that rabies is not a viable candidate for eradication.

Sensitive Surveillance

Effective surveillance to detect the circulation of disease in a population is crucial to eradication efforts. Although largely dependent on the existence of wellfunctioning health systems infrastructures, surveillance in an eradication context is also promoted by favorable disease characteristics (such as a predictable seasonality of incidence, visible symptoms, or short incubation period) and available technologies (inexpensive, rapid, and accurate serological tests). The World Health Organization (WHO) campaign to eradicate yaws in the 1950s failed in part due to the inability to identify infected persons. Because yaws can exist asymptomatically in a latent state, case finding was hampered and many such carriers relapsed to infectious states even after treatment teams had visited a community. Surveillance can also serve as an indicator of progress in eradication efforts. The first 10 years of the yaws campaign had little, if any, screening, and when serological surveys were finally conducted, the discovery of high prevalence of subclinical infections rendered the eradication campaign essentially futile.

Effective Interventions

Interventions for preventive or curative treatment are necessary to remove potential susceptible or infected persons from a population. In addition, disease-specific means of eliminating vectors are crucial. The WHO malaria eradication campaign from 1955 onward was an uphill battle due to chloroquine resistance by parasites, fostered in part by inconsistent prophylactic treatment at subtherapeutic levels that promoted selection of resistant strains over time. A main component of the eradication strategy targeted the mosquito vector through use of insecticides, relying heavily on DDT. However, growing vector resistance to insecticides reduced the effectiveness of insecticide-based preventive measures and ultimately was a factor in the WHO decision in 1969 to revise the goal of malaria eradication to simply control.

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