A serological evaluation of 1979-1982 Kenyan foot-and-mouth disease type SAT 2 viruses

Understanding what shapes disease control: An historical analysis of foot-and-mouth disease in Kenya

Interpreting the interplay between politics, social demographics and epidemiology is essential for understanding how a disease's occurrence and control evolve over time. Foot-and-mouth disease (FMD) virus was first detected in Kenya in 1915 and serotyped in 1932. This review aims to describe and appraise initiatives to control FMD in Kenya since its independence from British rule in 1964, using information from the scientific literature. We describe the historical dynamics of FMD epidemiology in the country and determine socio-political factors that have shaped the control strategies used. PubMed, Scopus, CAB abstracts, Science Direct, Web of Science and Google Scholar were used to search and retrieve papers, using predetermined search criteria encompassing FMD, Kenya and disease control programme descriptors. In total 1234 papers were identified and screened for relevance using the World Health Organization's guidelines for rapid review. Ultimately 69 references from this search were included, and information extracted and consolidated. These papers highlight that following independence, there was a structured effort to control FMD consisting of a compulsory subsidised vaccination programme in the Rift Valley with movement controls and quarantine when outbreaks occurred. This programme led to an initial decrease in recorded FMD outbreaks. However, endemic circulation continued and this programme was discontinued due to multiple factors, including political deprioritisation and changes in the structure of veterinary services. Only low levels of active surveillance have been applied since 1964; most surveillance is passive and relies on outbreak reports. Currently control focuses on outbreak management and a mixture of public- and privately-funded vaccination. This review highlights critical drivers influencing disease control programme implementation including veterinary service structure, the active participation of stakeholders with farming systems and availability of affordable and matched FMD vaccine. Additionally, it appraises the availability of historical information and draws attention to gaps in the historical record.

A novel method for performing antigenic vaccine matching for foot-and-mouth disease in absence of the homologous virus

Foot-and-mouth-disease (FMD) is a highly contagious transboundary animal disease that has negative consequences on regional and international trade. Vaccination is an important approach for FMD control and an essential consideration is the degree of cross-protection conferred by the vaccine against currently circulating field viruses. The objective of this study was to evaluate a new vaccine matching technique that does not require knowledge concerning the homologous vaccine virus. As a proof of concept, the vaccine-match was assessed for 41 FMD field viruses isolated from southern Africa over a 25-year period. A diverse group of 20 SAT1 and 21 SAT2 FMDV isolates collected from cattle and wildlife during 1991-2015 were selected for this study. Virus neutralization tests were performed against two sets of pooled sera for each serotype: vaccinated cattle sera (4-16 weeks post-vaccination) and convalescent cattle sera (3 weeks post-experimental challenge). Novel r₁-values were calculated as the ratio of the titre of the vaccinated sera to the titre for convalescent cattle sera. A validation r₁-value was calculated based on an assumption concerning the true homologous vaccine virus. There was a strong positive correlation between r₁-values for the novel and the validation methods for SAT1 viruses (Spearman's rho = 0.84, P < 0.01) and a very strong correlation for SAT2 viruses (Spearman's rho = 0.90, P < 0.01). In addition, there was moderate to good agreement between the novel and validation methods for both serotypes based on a r₁-value cut-off of 0.3, which is presumed to represent a good vaccine-match. The agreement between methods using prevalence-adjusted and bias-adjusted kappa (PABAK) was 0.67 and 0.84 for SAT1 and SAT2 viruses, respectively. The new r₁-value method provides a feasible, alternative vaccine matching approach that could benefit FMD control in southern Africa.

Unrecognized circulation of SAT 1 foot-and-mouth disease virus in cattle herds around Queen Elizabeth National Park in Uganda

Background

Foot-and-mouth disease (FMD) is endemic in Uganda in spite of the control measures used. Various aspects of the maintenance and circulation of FMD viruses (FMDV) in Uganda are not well understood; these include the role of the African buffalo (Syncerus caffer) as a reservoir for FMDV. To better understand the epidemiology of FMD at the livestock-wildlife-interface, samples were collected from young, unvaccinated cattle from 24 pastoral herds that closely interact with wildlife around Queen Elizabeth National Park in Uganda, and analysed for evidence of FMDV infection.

Results

In total, 37 (15 %) of 247 serum samples had detectable antibodies against FMDV non-structural proteins (NSPs) using a pan-serotypic assay. Within these 37 sera, antibody titres ≥ 80 against the structural proteins of serotypes O, SAT 1, SAT 2 and SAT 3 were detected by ELISA in 5, 7, 4 and 3 samples, respectively, while neutralizing antibodies were only detected against serotype O in 3 samples. Two FMDV isolates, with identical VP1 coding sequences, were obtained from probang samples from clinically healthy calves from the same herd and are serotype SAT 1 (topotype IV (EA-I)). Based on the VP1 coding sequences, these viruses are distinct from previous cattle and buffalo SAT 1 FMDV isolates obtained from the same area (19–30 % nucleotide difference) and from the vaccine strain (TAN/155/71) used within Uganda (26 % nucleotide difference). Eight herds had only one or a few animals with antibodies against FMDV NSPs while six herds had more substantial evidence of prior infection with FMDV. There was no evidence for exposure to FMDV in the other ten herds.

Conclusions

The two identical SAT 1 FMDV VP1 sequences are distinct from former buffalo and cattle isolates from the same area, thus, transmission between buffalo and cattle was not demonstrated. These new SAT 1 FMDV isolates differed significantly from the vaccine strain used to control Ugandan FMD outbreaks, indicating a need for vaccine matching studies. Only six herds had clear serological evidence for exposure to O and SAT 1 FMDV. Scattered presence of antibodies against FMDV in other herds may be due to the occasional introduction of animals to the area or maternal antibodies from past infection and/or vaccination.

The evidence for asymptomatic FMDV infection has implications for disease control strategies in the area since this obstructs early disease detection that is based on clinical signs in FMDV infected animals.

Electronic supplementary material

The online version of this article (doi:10.1186/s12917-015-0616-1) contains supplementary material, which is available to authorized users.

Predicting antigenic sites on the foot-and-mouth disease virus capsid of the South African Territories types using virus neutralization data

Foot-and-mouth disease virus (FMDV) outer capsid proteins 1B, 1C and 1D contribute to the virus serotype distribution and antigenic variants that exist within each of the seven serotypes. This study presents phylogenetic, genetic and antigenic analyses of South African Territories (SAT) serotypes prevalent in sub-Saharan Africa. Here, we show that the high levels of genetic diversity in the P1-coding region within the SAT serotypes are reflected in the antigenic properties of these viruses and therefore have implications for the selection of vaccine strains that would provide the best vaccine match against emerging viruses. Interestingly, although SAT1 and SAT2 viruses displayed similar genetic variation within each serotype (32 % variable amino acids), antigenic disparity, as measured by r(1)-values, was less pronounced for SAT1 viruses compared with SAT2 viruses within our dataset, emphasizing the high antigenic variation within the SAT2 serotype. Furthermore, we combined amino acid variation and the r(1)-values with crystallographic structural data and were able to predict areas on the surface of the FMD virion as antigenically relevant. These sites were mostly consistent with antigenic sites previously determined for types A, O and C using mAbs and escape mutant studies. Our methodology offers a quick alternative to determine antigenic relevant sites for FMDV field strains.

The implications of virus diversity within the SAT 2 serotype for control of foot-and-mouth disease in sub-Saharan Africa

SAT 2 is the serotype most often associated with outbreaks of foot-and-mouth disease (FMD) in livestock in southern and western Africa and is the only SAT type to have been recorded outside the African continent in the last decade. Its epidemiology is complicated by the presence of African buffalo (Syncerus caffer), which play an important role in virus maintenance and transmission. To assess the level of genetic complexity of this serotype among viruses associated with both domestic livestock and wildlife, complete VP1 gene sequences of 53 viruses from 17 countries and three different host species were analysed. Phylogenetic analysis revealed eleven virus lineages, differing from each other by at least 20 % in pairwise nucleotide comparisons, four of which fall within the southern African region, two in West Africa and the remaining five in central and East Africa. No evidence of recombination between these lineages was detected, and thus we conclude that these are independently evolving virus lineages which occur primarily in discrete geographical localities in accordance with the FMD virus topotype concept. Applied to the whole phylogeny, rates of nucleotide substitution are significantly different between topotypes, but most individual topotypes evolve in accordance with a molecular clock at an average rate of approximately 0.002 substitutions per site per year. This study provides an indication of the intratypic complexity of the SAT 2 serotype at the continental level and emphasizes the value of molecular characterization of diverse FMD field strains for tracing the origin of outbreaks.

Antigenic analysis of serotype O foot-and-mouth disease virus isolates from the Middle East, 1981 to 1988

During the period 1981-88 foot-and-mouth disease virus (FMDV) serotype O continued to be isolated from outbreaks in the Middle East. Field isolates submitted to the World Reference Laboratory have been examined in relation to reference strains by either complement fixation, virus neutralization or enzyme-linked immunosorbent assays. Most isolates were related to the European type O1 reference strains although strains emerging in late 1987 and 1988 were more closely related to O1/Manisa. In addition, FMDV isolates from Libya in 1981 and Syria in 1987 have shown very little relationship to these reference strains, although evidence of their persistence and spread has not been demonstrated.

Variation in foot-and-mouth disease virus isolates in Kenya: an examination of field isolates by T1 oligonucleotide fingerprinting

Ribonuclease T1 oligonucleotide maps of strains of 4 of the endemic serotypes of foot-and-mouth disease virus isolated in Kenya between 1964 and 1982 have been compared with data obtained in complement-fixation and neutralization tests. There was a continual change in the oligonucleotide maps obtained for all the serotypes examined. This genetic heterogeneity was generally associated with antigenic variation. Viruses isolated during the 12-month course of an epidemic of the SAT 1 serotype showed few changes in their oligonucleotide fingerprints, and were serologically related. These maps form a data base that will be useful in future epidemiological studies on the maintenance and spread of foot-and-mouth disease virus in this region.