A comparison of risk factor investigation and experts' opinion elicitation analysis for identifying foot-and-mouth disease (FMD) high-risk areas within the FMD protection zone of South Africa (2007-2016).

Foot-and-mouth disease is a controlled disease in accordance with the South African Animal Diseases Act (Act 35 of 1984). The country was classified by the World Organisation for Animal Health (WOAH) as having a FMD free zone without vaccination in 1996. However, this status was suspended in 2019 due to a FMD outbreak outside the controlled zones. FMD control in South Africa includes animal movement restrictions placed on cloven-hoofed species and products, prophylactic vaccination of cattle, clinical surveillance of susceptible species, and disease control fencing to separate livestock from wildlife reservoirs. The objectives of this study were to evaluate differences in identifying high-risk areas for FMD using risk factor and expert opinion elicitation analysis. Differences in risk between FMD introduction and FMD spread within the FMD protection zone with vaccination (PZV) of South Africa (2007-2016) were also investigated. The study was conducted in the communal farming area of the FMD PZV, which is adjacent to wildlife reserves and characterised by individual faming units. Eleven risk factors that were considered important for FMD occurrence and spread were used to build a weighted linear combination (WLC) score based on risk factor data and expert opinion elicitation. A multivariable conditional logistic regression model was also used to calculate predicted probabilities of a FMD outbreak for all dip-tanks within the study area. Smoothed Bayesian kriged maps were generated for 11 individual risk factors, overall WLC scores for FMD occurrence and spread and for predicted probabilities of a FMD outbreak based on the conditional logistic regression model. Descriptively, vaccine matching was believed to have a great influence on both FMD occurrence and spread. Expert opinion suggested that FMD occurrence was influenced predominantly by proximity to game reserves and cattle density. Cattle populations and vaccination practices were considered most important for FMD spread. Highly effective cattle inspections were observed within areas that previously reported FMD outbreaks, indicating the importance of cattle inspection (surveillance) as a necessary element of FMD outbreak detection. The multivariable conditional logistic regression analysis, which was consistent with expert opinion elicitation; identified three factors including cattle population density (OR 3.87, 95% CI 1.47-10.21) and proximities to game reserve fences (OR 0.82, 95% CI 0.73-0.92) and rivers (OR 1.04, 95% CI 1.01-1.07) as significant factors for reported FMD outbreaks. Regaining and maintaining an FMD-free status without vaccination requires frequent monitoring of high-risk areas and designing targeted surveillance.

A qualitative risk assessment of factors contributing to foot and mouth disease outbreaks in cattle along the western boundary of the Kruger National Park.

Between November 2000 and the end of 2007, five outbreaks of foot and mouth disease (FMD) occurred in cattle in the area adjacentto the Kruger National Park (KNP) in the north-eastern corner of South Africa. To help understand the factors behind these outbreaks a qualitative risk assessment based on the World Organisation for Animal Health (OIE) assessment framework was adopted, using available data from published sources and various unpublished South African sources. Risk was assessed on the basis of the following factors: data on South African Territories (SAT) type infections of buffalo and impala in the KNP, permeability of the fence along the western boundary of the KNP, the potential for contact between livestock and wildlife susceptible to FMD in areas adjacent to the KNP, and the level of herd immunity in cattle generated by prophylactic vaccination. Scenario pathways for FMD occurrence outside the KNP are presented as a conceptual framework to qualitatively assess the risk of FMD outbreaks. Factors that are likely to have most influence on the risk were identified: fence permeability, vaccination coverage, or the efficiency of animal movement control measures. The method and results are provided as an approach that may be used as a basis to evaluate the risk of FMD outbreaks occurring in other wildlife/livestock interface areas of southern Africa.

Influence of dipping practices on the seroprevalence of babesiosis and anaplasmosis in the foot-and-mouth disease buffer zone adjoining the Kruger National Park in South Africa.

A serological survey of bovine babesiosis and anaplasmosis was conducted in the foot-and-mouth disease buffer zone surrounding the Kruger National Park in South Africa between 2001 and 2003 to determine whether the withdrawal of government-subsidized dipping in certain regions had affected the seroprevalence of these tick-borne diseases. Seroprevalence of Anaplasma marginale and Babesia bovis increased during the study period. This increase was greater in Limpopo Province where farmers had to supply their own acaricide than in Mpumalanga Province where dipping materials were provided by the local Veterinary Services. The number of animals testing positive for B. bigemina decreased in both provinces during the study period, which was attributed to possible vector displacement rather than more effective tick control measures. Responses to a questionnaire on ticks and tick-borne diseases revealed local knowledge on the subject to be highly variable and sometimes incorrect.

Foot-and-mouth disease control using vaccination: South African experience.

South Africa has zoned status from the Office International des Epizooties (OIE) with the largest part of the country being foot-and-mouth disease (FMD)-free without vaccination. Outbreaks in this zone are handled differently from outbreaks in the control zones, which do not affect the export status of the country. However, the different socio-economic groupings need to be considered when reaching control decisions and in this regard, the country has been challenged with unique foot-and-mouth disease (FMD) control options. Vaccination has been shown to be effective both in ensuring that disease does not spread from the endemic to the free zone, as well as controlling outbreaks in the free zone. New adjuvants that claim to illicit longer lasting immunity have been tested with antigens derived from the SAT serotypes and animals were challenged one year post vaccination to determine the level of protection. However, even with vaccines that provide immunity for more than a year, an annual vaccination campaign will most probably not be acceptable in the buffer zone where calving occurs throughout the year.

Ixodid ticks on indigenous goats owned by small-scale farmers in four communal grazing areas in South Africa.

Indigenous goats belonging to small-scale farmers in 4 communal grazing areas in South Africa were sampled for ixodid ticks during the period September 1991 to May 1993. Three of these areas were in the North West Province (Rietgat, Madinyane and Bethany), and one in Mpumalanga Province (Geluk). No tick control was practised unless requested by the owners. Seven ixodid tick species, of which the majority were immature ticks, were collected from the goats in North West Province. Amblyomma hebraeum was the most numerous of these, followed by Rhipicephalus evertsi evertsi and Rhipicephalus appendiculatus. Substantially more ticks were collected from goats at Rietgat than at the Madinyane and Bethany grazing areas. Five tick species were collected at Geluk and R. evertsi evertsi comprised more than 95 % of the total population. At Rietgat and Geluk A. hebraeum nymphs were present on goats throughout the year, while most R appendiculatus nymphs were collected during September and October 1991 and most adults during January and February 1992. At both Rietgat and Geluk most immature R. evertsi evertsi were collected from spring to late summer, while adults were present throughout the year.

Ixodid ticks on cattle belonging to small-scale farmers at 4 communal grazing areas in South Africa.

Ixodid ticks were collected during the period September 1991 to August 1993 from cattle belonging to small-scale farmers utilising 4 communal grazing areas. Three of these were in North West Province and 1 in Mpumalanga province, South Africa. Ten tick species were collected in North West Province and 7 in Mpumalanga. The adults of Amblyomma hebraeum, Rhipicephalus appendiculatus and Rhipicephalus evertsi evertsi were most numerous in North West Province, while in Mpumalanga Boophilus decoloratus comprised more than 75% of the total population. Amblyomma hebraeum was present on all grazing areas, and heavy infestations of adults occurred during the period October to May on 1 of these. Few B. decoloratus were collected in North West Province, chiefly because the sampling method was inadequate, and most of these were present during early summer (October to December) and late summer and autumn (March to May). The initially low population of B. decoloratus in Mpumalanga increased substantially towards the conclusion of the survey, probably because of the cessation of dipping. Boophilus microplus was present in small numbers on 2 grazing areas in the North West Province. Adult Hyalomma marginatum rufipes reached peak numbers from December to February and Hyalomma truncatum from February to April in the North West Province. Only H. marginatum rufipes was collected in Mpumalanga. Rhipicephalus appendiculatus was present on all the grazing areas, with most adults present from December to April. Most adult Rhipicephalus evertsi evertsi were collected from September to April and Rhipicephalus simus was present during the period October-April.

Foot and mouth disease: the experience of South Africa.

Foot and mouth disease (FMD) is endemic in African buffalo (Syncerus caffer) in the Kruger National Park (KNP) and surrounding game parks in South Africa. The last outbreak of the disease in domestic stock outside the FMD control zone occurred in 1957. Due to the success in containing the disease, the country was accorded zone freedom from FMD without vaccination by the Office International des Epizooties (OIE: World organisation for animal health) in 1995. This status was lost in September 2000 when the first-ever recorded case of serotype O in South Africa was diagnosed in a piggery in KwaZulu-Natal after the illegal feeding of untreated swill. In November 2000, an outbreak of FMD caused by serotype South African Territories (SAT) 1 was diagnosed in a feedlot within the free zone of Mpumalanga Province. The SAT 1 outbreak was traced to cattle in the FMD control zone south of the KNP after the game-proof fence surrounding the KNP was severely damaged by floods. This enabled buffalo to come into direct contact with cattle outside the KNP. A further outbreak caused by SAT 2 was diagnosed within the FMD control zone in February 2001, also as a result of buffalo having escaped from the KNP. All these outbreaks were successfully contained, with the re-instatement of zone freedom from FMD without vaccination by the OIE in May 2002. These outbreaks made it necessary to re-examine the methods of control and containment of FMD that have been practised for many years and which are in line with accepted international practices. The authors describe the rationale for the different control strategies that were followed, the need for a multidisciplinary approach to disease control, the interface between control and technological and diagnostic support and the lessons learned. Some suggestions for future control strategies are also offered.

The absence of clinical disease in cattle in communal grazing areas where farmers are changing from an intensive dipping programme to one of endemic stability to tick-borne diseases.

A two-year field study was conducted in four communal grazing areas in South Africa. Sera were collected from young cattle (6-18 months old) in these areas during the winters of 1991 to 1993. The sera were tested for antibodies to Babesia bovis, Babesia bigemina, Anaplasma marginale and Cowdria ruminantium. In two of the four areas, treatment with acaricide was erratic and dependent on the discretion of individual owners. In these areas the drought of 1992 had a major impact on tick burdens and there were changes in the seroprevalence to tick-borne diseases. In the other two areas there was a reduction in the intensity of acaricide application and this was associated with an increase in seropositivity to the tick-borne diseases. Increases in the prevalence of seropositivity and the presence of endemic instability, as calculated from inoculation rates, were not accompanied by outbreaks of clinical disease. Possible reasons for this are discussed.