Serological studies of Foot and Mouth disease in selected areas of Uganda with a focus on situation in cattle

Abstract

Until this study, information on the epidemiology of foot-and-mouth disease (FMD) in livestock (specifically cattle) and wildlife in Uganda was very limited. Neither was there any detailed information on the seroprevalence of FMD in cattle. This PhD study was part of a wider research project funded by Danish International Development Agency (DANIDA) catering for four PhDs investigating the presence of FMD virus (FMDV) in livestock and wildlife in East Africa. This study investigated serotype-specificity of antibodies against FMDV and sero-prevalences of antibodies against FMDV, as well as performance of two commercial test kits for antibodies against FMDV from Cedi Diagnostics in these animals in different geographic localities in Uganda.

To evaluate serotype-specificity of antibodies against FMDV circulating in the South Western and Western regions of Uganda, samplings were carried out on blood and orolpharyngeal fluids following a major outbreak of FMD in 2006, as well as in an attempted comprehensive random sampling in the two districts of Kasese and Bushenyi bordering Queen Elisabeth National Park in 2007 and in a post outbreak sampling in an area surrounding Lake Mburo National Park in 2008. Circulating antibodies towards FMDV were investigated based on screening of cattle sera using two commercial kits for antibodies against FMDV (Ceditest® FMDV-NS and Ceditest® FMDV type O, both Cedi Diagnostics BV, Lelystad, The Netherlands). Serotype-specificity of antibodies elicited against FMDV were determined using Solid Phase Blocking ELISAs (SPBE) for the seven FMDV serotypes (O, A, C, Asia 1, SAT 1, SAT 2 and SAT 3).

In 2006, high overall prevalences of antibodies against non-structural proteins (NSP) of FMDV (78%, n=222/285) and structural proteins (SP) of FMDV serotype O (SP-O) (83%, n=235/285) were demonstrated in herds with typical visible clinical signs of FMD, while overall prevalences for antibodies against NSP (5%, 3/64) and SP-O (4%, 4/64) were much lower in herds without clinical signs of FMD. With regard to serotypespecific antibodies, the investigated sera had highest seroprevalence of antibodies against serotype O, followed by antibodies against serotypes SAT 1, SAT 2 and SAT 3 in decreasing order. Only FMDV serotype O virus was isolated from two probang samples. In 2007, a prevalence study to assess antibodies against FMDV in cattle was conducted in the districts of Kasese and Bushenyi in Western Uganda using the ELISA assays described above. A total of 309 sera samples were collected and tested for antibodies against NS and SP using the CEDI test kits. Sero-prevalences of antibodies against NS and SP-O were much higher in Kasese (61% and 43%, respectively) than in Bushenyi (3% and 4%, respectively). Of the sera subjected to SPBE ELISAs, the prevalence of serotype-specific antibodies against FMDV was highest for serotype O, followed by SAT 1, SAT 3 and SAT 2 in decreasing order. In 2008, antibodies against FMDV in cattle in surrounding areas of Lake Mburo National Park (LMNP) in South-Western Uganda were investigated using the ELISA assays as described above. Of the sera tested, 42.7% (90/211) and 75.4% (159/211) were positive for antibodies against NSP and SP-O, respectively. Sero-prevalences of antibodies against the seven FMDV serotypes using a cut-off at titre ≥ 1:160 were 61% (19/31), 33% (5/15), 0%, 0%, 70% (23/33), 34% (11/32) and 12% (4/33) for serotypes O, A, C, Asia 1, SAT 1, SAT 2 and SAT 3, respectively. It was concluded that most of the previous FMD outbreaks in the areas surrounding LMNP were caused by FMDV serotype O, A and SATs, and that it could not be determined whether the measured antibodies were elicited by vaccination or infection, since all sampled cattle were above 4 years of age, and non-purified trivalent vaccines including FMDV serotypes O, SAT 1 and SAT 2 were regularly used in the area. The study also evaluated the performance of Ceditest® NS and Ceditest® FMDV type O ELISA kits for detecting antibodies against FMDV in buffalos, cattle, goats and sheep in Uganda. Highest seroprevalence was measured with the Ceditest® NS in buffalos, while Ceditest® FMDV type O test found the highest seroprevalence in cattle. Further comparison of SP-O test with SPBE revealed differences in serotype specificity with higher antibody titres against the SAT-serotypes biased towards SPBE than against SPO both in buffalos and cattle. Goats had the lowest seroprevalence of antibodies in both the Ceditest® NS and the Ceditest® FMDV type O test. Based on this investigation, it could not be recommended to use the Ceditest® FMDV type O test in East African animal populations where the SAT-serotypes of FMDV are prevalent. This test kit can be used in combination with the NSP test when investigating outbreaks of FMDV caused by serotype O, however, it will not be possible to differentiate between vaccinated and infected animals as long as non-purified vaccines are regularly applied in the region.

In general, it is recommended that more regional studies be carried out to establish the whole spectrum of FMDV serotypes and/or strains involved in disease outbreaks. Furthermore, the ELISAs (SPBE) should be standardized to avoid impending cross reactions as was observed in the study.