Disease Surveillance Investments and Administration: Limits to Information Value in Pakistan Polio Eradication.

In Pakistan, annual poliovirus investment decisions drive quantities of supplemental immunization campaigns districts receive. In this article, we assess whether increased spending on poliovirus surveillance is associated with greater likelihood of correctly identifying districts at high risk of polio with assignment of an elevated "risk ranking." We reviewed programmatic documents from Pakistan for the period from 2012-2017, recording whether districts had been classified as "high risk" or "low risk" in each year. Through document review, we developed a decision tree to describe the ranking decisions. Then, integrating data from the World Health Organization and Global Polio Eradication Initiative, we constructed a Bayesian decision network reflecting investments in polio surveillance and immunization campaigns, surveillance metrics, disease incidence, immunization rates, and occurrence of polio cases. We test these factors for statistical association with the outcome of interest-a change in risk rank between the beginning and the end of the one-year time period. We simulate different spending scenarios and predict their impact on district risk ranking in future time periods. We find that per district spending increases are associated with increased identification of cases of acute flaccid paralysis (AFP). However, the low specificity of AFP investment and the largely invariant ranking of district risk means that even large increases in surveillance spending are unlikely to promote major changes in risk rankings at the current stage of the Pakistan polio eradication campaign.

Emergence and re-emergence of viral diseases of the central nervous system.

Neurologic disease is a major cause of disability in resource-poor countries and a substantial portion of this disease is due to infections of the CNS. A wide variety of emerging and re-emerging viruses contribute to this disease burden. New emerging infections are commonly due to RNA viruses that have expanded their geographic range, spread from animal reservoirs or acquired new neurovirulence properties. Mosquito-borne viruses with expanding ranges include West Nile virus, Japanese encephalitis virus and Chikungunya virus. Zoonotic viruses that have recently crossed into humans to cause neurologic disease include the bat henipaviruses Nipah and Hendra, as well as the primate-derived human immunodeficiency virus. Viruses adapt to new hosts, or to cause more severe disease, by changing their genomes through reassortment (e.g. influenza virus), mutation (essentially all RNA viruses) and recombination (e.g. vaccine strains of poliovirus). Viruses that appear to have recently become more neurovirulent include West Nile virus, enterovirus 71 and possibly Chikungunya virus. In addition to these newer challenges, rabies, polio and measles all remain important causes of neurologic disease despite good vaccines and global efforts toward control. Control of human rabies depends on elimination of rabies in domestic dogs through regular vaccination. Poliovirus eradication is challenged by the ability of the live attenuated vaccine strains to revert to virulence during the prolonged period of gastrointestinal replication. Measles elimination depends on delivery of two doses of live virus vaccine to a high enough proportion of the population to maintain herd immunity for this highly infectious virus.