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. 2014 Dec 4:7:574.
doi: 10.1186/s13071-014-0574-7.

Temporal fluctuations in the sero-prevalence of Taenia solium cysticercosis in pigs in Mbeya Region, Tanzania

Uffe Christian Braae  1 , Pascal Magnussen  2   3 , Faustin Lekule  4 , Wendy Harrison  5 , Maria Vang Johansen  6
Affiliations

Temporal fluctuations in the sero-prevalence of Taenia solium cysticercosis in pigs in Mbeya Region, Tanzania

Uffe Christian Braae et al. Parasit Vectors. .

Abstract

Background: Porcine cysticercosis is an emerging agricultural problem in sub-Saharan Africa. This has been documented primarily through cross-sectional studies, however detailed knowledge of the transmission dynamics of this disease in sub-Saharan Africa is lacking. This study aims to describe seasonal variations in sero-prevalence of antigen ELISA positive porcine cysticercosis in an endemic area.

Methods: A longitudinal study composed of three cross-sectional surveys was carried out in Mbeya Region, Tanzania; the first two six months apart (March/April 2012 and October/November 2012) and the last eight months later (July/August 2013). Venous blood was collected from pigs in 22 villages and analysed using Ag-ELISA.

Results: In each survey between 800-1000 serum samples were collected. The first survey revealed a cysticercosis sero-prevalence of 15% (n = 822, 95% CI: 13-18%). The sero-prevalence had significantly increased to 24% (p < 0.001, χ2-test, n = 812, 95% CI: 21-27%) at the time of the 6 month follow-up. At 14-months the sero-prevalence had dropped to 20% (p = 0.053, χ2-test, n = 998, 95% CI: 18-23%). Overall, this was a reduction in sero-prevalence compared with a study conducted in 2007 in the same area, where 31% (186/600) of pigs were found positive.

Conclusion: Confined pigs did not have a lower sero-prevalence compared to free roaming pigs in any of the three surveys. Several factors may have contributed to the observed fluctuations such as African swine fever or seasonal variation in local crop production practices. Also, as the Ag-ELISA assay used is not species specific, variation in transmission of Taenia hydatigena could potentially influence the results. The observed fluctuations contradict a theoretical model which predicts a stable equilibrium, which only considers a two-compartment (pig and human) model excluding the effect of the environment. Whether the disease has an endemic equilibrium, or undergoes fluctuations dependent on extrinsic and/or socio-economic factors remains to be elucidated.

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Figures

Figure 1
Figure 1
Theoretical risk of infection based on pig production system. The theoretical risk of infection is set to arbitrary values from low to high based on the likelihood of free-range being practised, which is based on rainfall in Mbeya Region that determines planting seasons and therefore when free-range is practised. The theoretical detection of infection is based on risk of infection and a test sensitivity of 80% with one month lag due to the 2–6 weeks it takes for antigen levels to reach detectable levels in infected pigs. The three surveys are placed according to the time of year they were carried out and not in chronological order.
Figure 2
Figure 2
Proportion of pigs kept under each specific production system during each sampling round. Sample size = n. Error bars represent the standard error in percentage points.
Figure 3
Figure 3
Overall sero-prevalence of porcine cysticercosis and sero-prevalence within each production system with total number of pigs as the denominator. Sample size = n. Error bars represent the standard error in percentage points.
Figure 4
Figure 4
Sero-prevalence of porcine cysticercosis measured for each type of production system with number of sampled pigs from the respective production system as the denominator. Sample size = n. Error bars represent the standard error in percentage points.
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