Epidemiology, control and potential insect vectors of Trypanosoma evansi (surra) in village livestock in southern Philippines

The objective of this project was to determine the extent and impact of infection with Trypanosoma evansi in livestock in Mindanao, Philippines, evaluate economic benefits of control options and determine its vectors. The project was undertaken because of insufficient knowledge on the dynamics and impact of surra in livestock in the island and because sporadic serious epidemics have occurred in recent years despite the implementation of control measures. Data from cross-sectional surveys conducted in 2002-6 involving more than 2,000 animals were utilized to estimate the impact of T. evansi infection in buffalo populations. A bio-economic infectious disease model was also developed using these data and data from follow up surveys to evaluate economic losses and benefits of control of T. evansi in different animal hosts. Trypanosoma evansi infection caused significant negative impact on buffalo populations with high mortality and reproductive losses. The estimated financial losses from T. evansi infection are high. However, targeted treatment of all sick animals throughout the year using a highly effective drug would have substantial benefits. The estimated annual total financial net benefit from an effective surra control for a typical village in a moderate/high-surra risk area in Mindanao was US $158,000. The value added to buffaloes, cattle, horses, goats/sheep and pigs as a result of this control was US $88, $84, $151, $7, $114 per animal per year, respectively. Follow up surveys were conducted in 2007-8 to determine the prevalence of T. evansi infection in 2,383 buffaloes and other animals (290 goats, 226 cattle, 151 pigs and 35 horses) from 73 villages in Mindanao, investigate associations between T. evansi and other pathogens (Neospora caninum and Brucella abortus) with reproductive failure and calf mortality in buffalo cows, and to confirm the presence of RoTat 1.2 gene in 168 local isolates of T. evansi. Trypanosoma evansi was detected using MHCT, MIT, PCR and CATT in livestock in a number of high-surra risk areas with 59%, 41%, 41%, 35% and 25% seroprevalence in buffaloes, cattle, horses, goats and pigs, respectively. Trypanosoma evansi was associated with reproductive failure and early calf mortality in buffalo cows. The RoTat 1.2 gene was detected in all 168 local isolates of T. evansi tested but was probably not expressed in all cases. The seroprevalence and impact of combined infections of T. evansi and F. gigantica were determined in 1,163 buffaloes from 32 villages in high- and low-surra risk areas in Mindanao. Fasciola gigantica infection was highly prevalent in buffaloes in both areas and combined infections of T. evansi and F. gigantica were highly prevalent in high-surra risk villages. Buffaloes that were seropositive to T. evansi infection were more likely to be seropositive with F. gigantica than uninfected buffaloes and combined infections were associated with poor body conditions and low PCV. Trapping of tabanids was conducted in 2007-8 in selected villages in high-and low-surra risk provinces to determine the local tabanid fauna and their abundance, detect trypanosomes in tabanids and determine the hosts of the flies using genetic markers. All five species of trapped tabanids were more abundant in low- than high-altitude areas and abundance was significantly associated with high rainfall. Trypanosoma evansi and T. theileri were detected from at least one fly of every tabanid species caught. Buffaloes, pigs, goats, humans and chickens were identified as hosts of tabanids in Mindanao. There is a need to identify tabanid fauna in other areas in Mindanao and confirm their active role in the transmission of T. evansi in livestock. Results support the conclusions that: (a) Trypanosoma evansi infection causes significant economic losses in livestock in Mindanao but its effective control would provide substantial financial benefits; (b) Trypanosoma evansi infection is highly prevalent in livestock in Mindanao which is highly associated with poor reproduction performance in buffaloes; (c) RoTat 1.2 based tests (PCR and CATT) are applicable in the diagnosis of surra in Mindanao but the value of the CATT still requires further evaluation; (d) Fasciolosis needs to be included in the control strategy for surra in high risk areas; and, (e) Tabanids identified in Mindanao are potential transmitters of T. evansi and their control should be explored. There is a need, therefore, to sustain surveillance and implement an integrated and more effective control programme against T. evansi infection in livestock in Mindanao.