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Elimination &MDA &NTDs &poverty &Schistosomiasis &Trachoma &Vector Control Bill Brieger | 13 Jun 2023 09:20 am

Eliminating NTDs as a Public Health Problem May Not Be Enough

The concept and goal of eliminating a disease appears simple on the surface, but complications ensue when the words “as a public health problem” are added.  We know that the distinction exists between eradication and elimination with the former being globally and the latter being nationally or regionally. The sum total action of eliminating a disease from all endemic countries therefore results in total global eradication.

The challenge comes when we try to qualify the concept of elimination. The US CDC defined elimination of disease as, “Reduction to zero of the incidence of a specified disease in a defined geographical area as a result of deliberate efforts; continued intervention measures are required.” Thus, there is no more transmission.  Following from this eradication is defined as, “Permanent reduction to zero of the worldwide incidence of infection caused by a specific agent as a result of deliberate efforts; intervention measures are no longer needed.” Penn Medicine summarized this as, “Elimination means stopping the transmission of a disease in a specific geographic area or country, but not worldwide. Elimination is a crucial step in the path toward eradication, requiring constant monitoring and interventions to keep serious diseases at bay.”

The foregoing definitions seem straightforward, but what does elimination as a public health problem or a disease of public health concern mean? The World Health Organization recently “congratulate(d) Benin and Mali for eliminating trachoma as a public health problem. Concerning another neglected tropical disease (NTD), lymphatic filariasis (LF), global control programs are aiming “to reduce the prevalence of infection below target thresholds and to alleviate the suffering of people affected by lymphoedema and hydrocele.” Wiegand and colleagues in The Lancet Global Health note that, “For schistosomiasis, the criterion for elimination as a public health problem (EPHP) is defined as less than 1% prevalence of heavy-intensity infections (ie, ?50 Schistosoma haematobium eggs per 10 mL of urine or ?400 Schistosoma mansoni eggs per g of stool).” They take issue with the fact that such definitions mean that morbidity still exists, though at very levels, so elimination of transmission has not really occurred for any of these NTDs.

Because the social, environmental, and behavioral conditions that favor transmission may still exists, one cannot guarantee that incidence such diseases may not increase again. All three diseases, LF, Schistosomiasis, and Trachoma have been tackled primarily through preventive chemotherapy, is simply put, using mass drug administration (MDA) over a period of years until active surveillance determines that “infection (is) below target thresholds.” Trachoma does have its SAFE strategy which includes water, sanitation and hygiene interventions, but drugs can reduce the disease without long term achievements in such activities have become sustainable.

Prada et al. in the Journal of Infectious Diseases warn that there can be resurgence of a disease that was documented to be eliminated as a public health problem. They explain that the transmission assessment survey held after several MDA rounds for LF may not be enough to guarantee that low levels of transmission and eventual elimination are achieved. They conclude that, “The risk of resurgence after achieving current targets is low and is hard to predict using just current prevalence. Although resurgence is often quick (<5 years), it can still occur outside of the currently recommended post-intervention surveillance period of 4–6 years,” and recommend monitoring beyond this period.

Toor and co-researchers suggest for NTD programs that, “as case numbers drop and elimination comes into prospect, transmission reduction through other interventions, such as vector control and sanitation, becomes crucial in reducing the probability and speed of resurgence, particularly when MDA or screening programs are halted. Surveillance activities for detecting elimination and resurgence become increasingly important to ensure that successes are maintained.”

Ultimately, unless the context of NTD transmission is addressed, elimination will be an elusive goal. Therefore, as WHO advocated on the recent World NTD Day, “Everybody, including leaders and communities, to confront the inequalities that drive NTDs and to make bold, sustainable investments to free the world’s most vulnerable communities affected by NTDs from a vicious cycle of disease and poverty.”

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