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. 2018 Feb;24(2):210-220.
doi: 10.3201/eid2402.160122.

Ecologic Features of Plague Outbreak Areas, Democratic Republic of the Congo, 2004-2014

Ecologic Features of Plague Outbreak Areas, Democratic Republic of the Congo, 2004-2014

Aaron Aruna Abedi et al. Emerg Infect Dis. 2018 Feb.

Abstract

During 2004-2014, the Democratic Republic of the Congo (DRC) declared 54% of plague cases worldwide. Using national data, we characterized the epidemiology of human plague in DRC for this period. All 4,630 suspected human plague cases and 349 deaths recorded in DRC came from Orientale Province. Pneumonic plague cases (8.8% of total) occurred during 2 major outbreaks in mining camps in the equatorial forest, and some limited outbreaks occurred in the Ituri highlands. Epidemics originated in 5 health zones clustered in Ituri, where sporadic bubonic cases were recorded throughout every year. Classification and regression tree characterized this cluster by the dominance of ecosystem 40 (mountain tropical climate). In conclusion, a small, stable, endemic focus of plague in the highlands of the Ituri tropical region persisted, acting as a source of outbreaks in DRC.

Keywords: Democratic Republic of the Congo; Plague; Yersinia pestis; bacteria; ecology; environment; epidemiology; risk factors; zoonoses.

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Figures

Figure 1
Figure 1
Timeline of plague cases, Orientale Province, Democratic Republic of the Congo, 1928–2014 (,–7). A) 1928: Detection of the first cases of plague in Ituri. B) 1933: First epidemiologic studies on plague. C) 1960: Independence of DRC, followed by the departure of expatriates dedicated to the fight against the plague. D) 1966: Armed conflicts in Ituri. E) 1968: End of postindependence conflicts. F) 1975: Surveillance and control assigned to the Ministry of Environment. G) 1979: Dereliction of control and reporting activities in Ituri. H) 1984: Control activities assigned to the Ministry of Health. I) 1987: First large epidemic episode, mostly in Ituri. J) 1996: Beginning of armed conflicts: first Congo war (1996), second Congo war (1999), and Ituri conflict (2003). K) 2003: Weakening of armed conflicts. Population data for former Kivu (corresponding to Maniema, North Kivu, and South Kivu) and Haut-Zaire (corresponding to Orientale Province) were calculated by smoothing data between the years with a known estimate (1947, 1955, 1975, 1984, 2000). Incidence is per 100,000 population.
Figure 2
Figure 2
Location of spatial clusters of bubonic and pneumonic plague, Orientale Province, Democratic Republic of the Congo, 2004–2014. Yellow circles indicate clusters of health zones determined by spatial scan analysis. p values were <0.001, except for Wamba (p = 0.053). First inset shows the Ituri cluster constrained by frontiers; Oliveira F was 1 for Linga, Logo, Rethy, and Rimba and 0.69 for Fataki. Second inset shows location of DRC in Africa. The 4 ecosystems follow those described at http://www.fao.org/ag/AGAInfo/programmes/documents/livatl2/Ecosystems.htm (Technical Appendix Table).
Figure 3
Figure 3
Temporal distribution of bubonic and pneumonic plague (A) and location of pneumonic plague outbreaks (B), Orientale Province, Democratic Republic of the Congo, 2004–2014. Five episodes of pneumonic plague outbreaks were observed; *, Ganga, 2005; †, Rethy and Linga, 2006; ‡, Wamba, 2006; §, Mahagi+Logo, 2007; ¶, Logo, 2014.. Ganga and Wamba experienced pneumonic plague only, after an increase of cases in the highlands of Ituri (enlarged area in B). Linga, Rethy, Mahagi, and Logo report bubonic plague all year but experienced outbreaks of pneumonic plague in 2006, 2007, and 2014.
Figure 4
Figure 4
Yearly distribution of bubonic plague in Ituri and Haut-Uele districts, Orientale Province, Democratic Republic of the Congo, 2004–2014. The 2 eastern districts of Orientale Province (Ituri in the south and Haut-Uele in the north) were the only districts reporting bubonic plague during the study period. Highlands of Ituri had suspected cases every year. Incidence is per 100,000 population.
Figure 5
Figure 5
Time series decomposition using LOESS regression for bubonic plague, Orientale Province, Democratic Republic of the Congo, 2004–2014. Plague did not vary seasonally. The trend was decreasing after 2006. Remainder (residuals) explained 63% of model variance, trend 22% and seasonality 8% only.
Figure 6
Figure 6
Classification of health zones according to environmental factors related to bubonic plague, Orientale Province, Democratic Republic of the Congo, 2004–2014. A) Classification and regression tree analysis of plague cases determined a significant (p = 0.015) high-risk class of 7 health zones (class 2). Health zones in class 2 have>72.7% of their territory in the mountain tropical climate. The increase in risk for class 2 compared with class 1 was not significant when analyzed with a generalized additive model (incidence rate 1.79; p = 0.14). B) Locations of class 2 zones within Orientale Province. Class 2 zones were grouped in the highlands of Ituri. The cluster determined by spatial scan statistics in the Ituri Highlands ("SaTScan cluster") was composed entirely of class 2 health zones.

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