Smallpox eradication in Bangladesh, 1972-1976

Abstract

Rahima Banu, the world's last endemic case of severe smallpox, Variola Major, developed rash on October 16, 1975 on Bhola Island, Bangladesh. Achieving eradication in a country destroyed by war challenged the achievement of smallpox eradication. Between January 1, 1972 and December 31, 1975, 225,000 smallpox cases and 45,000 smallpox deaths occurred. Adapting the global smallpox eradication strategies of surveillance, the detection of smallpox cases, and containment, the interruption of smallpox transmission, utilized progress toward three objectives to monitor performance: (1) surveillance - the percent of smallpox infected villages detected within 14 days of the first case of rash, (2) knowledge of the reward - public knowledge of the current amount of the reward for reporting smallpox, and (3) containment - the percent of infected villages interrupting smallpox transmission within 14 days of detection. Failures to achieve these objectives led to the identification and implementation of improved strategies that eventually achieved eradication. Essential to this success was a tripartite partnership of the citizens of Bangladesh, the Bangladesh Ministry of Health, its field staff, and staff and resources mobilized by the World Health Organization.

Figure 1

Geographic distribution of smallpox infected villages in Bangladesh. The distribution of infected villages during October 1974 (Figure 1A), January 1975 (Figure 1B), March 1975 (Figure 1C), and April1975 (Figure 1D) illustrates the spatial spread of smallpox throughout Bangladesh following reintroduction.

Figure 1

Geographic distribution of smallpox infected villages in Bangladesh. The distribution of infected villages during October 1974 (Figure 1A), January 1975 (Figure 1B), March 1975 (Figure 1C), and April1975 (Figure 1D) illustrates the spatial spread of smallpox throughout Bangladesh following reintroduction.

Figure 1

Geographic distribution of smallpox infected villages in Bangladesh. The distribution of infected villages during October 1974 (Figure 1A), January 1975 (Figure 1B), March 1975 (Figure 1C), and April1975 (Figure 1D) illustrates the spatial spread of smallpox throughout Bangladesh following reintroduction.

Figure 1

Geographic distribution of smallpox infected villages in Bangladesh. The distribution of infected villages during October 1974 (Figure 1A), January 1975 (Figure 1B), March 1975 (Figure 1C), and April1975 (Figure 1D) illustrates the spatial spread of smallpox throughout Bangladesh following reintroduction.

Figure 2

Smallpox infected villages and cases in Bangladesh, 1974-75. Smallpox incidence, as evidenced both by the number or infected villages and reported smallpox cases, increased from February to June in 1974 and September 1975.

Figure 3

Results from the retrospective survey of smallpox facial scars conducted during 1976. Reported and unreported smallpox cases and percentages of the estimated annual totals that were reported each year in Bangladesh, 1972-75, the stacked bars and numbers, respectively.

Figure 4

Secular improvement in smallpox reporting. The logistic equation, y(t) = 1/[1 + exp(3.24 - 1.01t)], where t = time in years since 1 January 1971, was fitted to ratios of cases reported and estimated via the 1976 pockmark survey [3], the curve and points, respectively.

Figure 5

Cases reported and estimated by correcting for reporting inefficiency. To estimate the actual numbers of cases, reports were multiplied by reciprocals of efficiencies obtained from the function illustrated in Figure 4, the solid and dashed lines with ‘×’ and ‘o’ symbols, respectively.

Figure 6

Smallpox cases predicted by the transmission model [2] and “observed” in Bangladesh, 1972-75. The symbols represent daily estimates obtained from the corrected monthly observations illustrated in Figure 5, adjusted to match the annual totals of Hughes and co-workers [3].

Figure 7

Impact of improved surveillance and containment on the reproduction number. Learning from failures reduced the average number of secondary infections per primary infection, the dotted line, which eventually converged on the threshold for elimination, the solid line.

Figure 8

Failures to stop transmission within 14 days, Bangladesh 1974-75. Monthly percentages of villages having new smallpox cases 15 or more days after identification of smallpox infected village. The decrease in containment failures documents the increased timeliness and effectiveness of containment tasks.