A survey to investigate movements off sheep and cattle farms in New Zealand, with reference to the potential transmission of foot-and-mouth disease

AIM

To quantify the numbers and extent of movements off sheep and cattle farms in New Zealand, in order to construct more realistic simulation models to investigate how infectious diseases such as foot-and-mouth disease (FMD) might spread.

METHODS

Farmers from 500 randomly selected farms, comprising 100 from each of the following sectors, viz beef, dairy, grazing/dairy heifer rearing, sheep, and mixed sheep and beef, were asked to fill in diaries in which they recorded the movements of all animals, products, people, vehicles and equipment coming on to or leaving their farms during two separate 3-week periods, representing relatively 'busy' and 'quiet' times of the year with respect to livestock movements. Where possible, the destination of each movement was identified and geo-coded, to allow the distance travelled to be calculated. Each movement was then classified according to the risk of transfer of FMD virus (FMDV), should the disease have been present on the study farm at the time of the movement. The data were then analysed to establish movement frequencies and distributions of distances travelled, by the different pastoral livestock sectors.

RESULTS

Two hundred and seventeen farmers returned one or more diaries. One hundred and ninety-three farmers completed a Busy-period diary, recording a total of 12,052 movements off their farms, a crude average of 62.4 per 3-week period, or 2.97 per day. Of these, 4.0% involved the transport of livestock, equating to 0.12 livestock consignments per day. In contrast, 186 Quiet-period diaries were returned, recording a total of 10,885 movements off, representing a crude average of 58.5 during the 3-week period, or 2.78 per day. Of these, 2.1% involved livestock, equating to 0.06 livestock consignments per day. The mean and median distances travelled during the Busy periods were 30.9 km and 13.1 km, respectively (range 0-1,167 km). In comparison, the mean and median distances travelled during Quiet periods were 41.3 and 14 km, respectively (range 0.4-1,203 km).

CONCLUSIONS

People, vehicles, livestock and other items can travel off pastoral livestock farms in New Zealand to other farms either directly or via saleyards over extensive distances. This has implications for the potential spread of infectious diseases such as FMD. Movement parameters intended for use in the InterSpread Plus inter-farm simulation model of FMD were established, which will facilitate the prediction of likely spread and efficacy of controls in the unlikely event of a real-life outbreak.

John Burns Brooksby CBE: 25 December 1914 - 17 December 1998

John Brooksby was an outstanding veterinary virologist, who worked at the Animal Virus Disease Research Institute, Pirbright, for 40 years, for 16 of which he was Director of the Institute. He will be remembered for his contributions to the diagnosis of foot-and-mouth disease, for his discovery of four new types, for the classification of subtypes and for fundamental studies of the virus. As Deputy Director and Director he was responsible for programmes on fundamental investigations of foot-and-mouth disease virus and other viruses exotic to the UK and for the application of the results both in the UK and worldwide. His advice on the distribution and the control of foot-and-mouth disease was sought by international organizations and by individual countries and was responsible for reducing the risk of spread of disease.

Comparisons of original laboratory results and retrospective analysis by real-time reverse transcriptase-PCR of virological samples collected from confirmed cases of foot-and-mouth disease in the UK in 2001

There were 2030 designated cases of foot-and-mouth disease (FMD) during the course of the epidemic in the UK in 2001 (including four from Northern Ireland). Samples from 1720 of the infected premises (IPs) were received in the laboratory and examined for either the presence of FMD virus (virological samples from 1421 IPs) or both FMD virus and antibody (virological and serological samples from 255 IPs) or antibody alone (from 44 IPs). The time taken to issue final diagnostic results ranged from a few hours in cases in which positive results were obtained by ELISA on epithelia containing sufficient virus to be detected, to several days for samples containing small amounts of virus requiring amplification through cell culture, negative samples or samples tested for antibody. Two subsets of samples were analysed retrospectively by real-time reverse transcriptase-PCR (RT-PCR); first, epithelia that were negative by both ELISA and virus isolation (VI) in cell culture, and secondly, samples that were negative by ELISA on epithelial suspension but positive by VI. There was broad agreement between the RT-PCR and VI/ELISA combined, except that the RT-PCR procedure did not detect a group of related virus isolates from Wales. These viruses had evidently evolved during the epidemic and had a nucleotide substitution in the RT-PCR probe site, which prevented them from being detected by the routine diagnostic probe. No evidence of FMD virus, antibody or nucleic acid was found in approximately 23 per cent (390 of 1730) of IPs from which samples were received, suggesting that the incidence of FMD during the outbreak may have been over-reported.

Foot-and-Mouth Disease: Host Range and Pathogenesis

In this chapter the host range of foot-and-mouth disease (FMD) under natural and experimental conditions is reviewed. The routes and sites of infection, incubation periods and clinical and pathological findings are described and highlighted in relation to progress in understanding the pathogenesis of FMD.

Spatial statistical modeling of disease outbreaks with particular reference to the UK foot and mouth disease (FMD) epidemic of 2001

In this paper we examine issues relating to the analysis of spatially-referenced disease data. Initially, we discuss the use of exploratory statistical tools such as density estimation and nonparametric regression. We then consider the need for descriptive epidemic models in space, time, and space-time models for epidemic dynamics. Implicitly space-time must be considered in any analysis of the spatial structure of epidemics. The use of Bayesian models for disease spread is discussed and applied to the recent foot and mouth outbreak in the UK.

Use of the scan statistic on disaggregated province-based data: Foot-and-mouth disease in Iran

The spatial scan statistic was applied to density-smoothed data that approximated the spatial distribution within the area and reduced the potential bias produced when location data have been aggregated for large areas. The method is illustrated, using data on the location of foot-and-mouth disease (FMD) outbreaks in Iran. Data examined were 4477 FMD outbreaks reported on a per province basis between June 1996 and September 2003. A kernel density of the outbreak locations was estimated, using a fixed radius and the centroid of each province as the designated location of all cases reported for the province. The radius that produced a density map with the highest correlation with expert opinion was 4 degrees (latitude/longitude). Livestock density was used as a proxy for the underlying population at risk of acquiring FMD. Livestock and outbreak density maps were overlain to obtain the number of outbreaks and livestock in each of 15,599 cells covering the mapped surface of the country. A spatial scan statistic was applied to the density-smoothed data assuming that the outbreaks had a Poisson distribution. Results were compared with those obtained using a spatial scan statistic on provincially aggregated data. Application of the spatial scan statistic on the density-smoothed data allowed identification of clusters (P<0.01) related more to the actual geographic distribution of cases (expert opinion) and of animals at risk, than to the distribution of the provinces. Significant clusters of FMD were identified that coincided with roads, neighboring countries, and high-density population areas, suggesting that the region may represent a route for cross-continent transmission of FMD.

The 2001 epidemic of foot-and-mouth disease in the United Kingdom: epidemiological and meteorological case studies

The possibility of the airborne spread of foot-and-mouth disease during the 2001 epidemic in the uk has been investigated in three epidemiological case studies. On the basis of evidence from field investigations, and a simple meteorological analysis, it is concluded that the spread of disease was consistent with the airborne transport of virus. The distances ranged from less than 1 km to 16 km; six of the farms were over 6 km from the source and involved the passage of virus over the sea combined with meteorological conditions which strongly favoured airborne disease transmission. The results of detailed atmospheric modelling demonstrated that airborne virus could have challenged livestock on all the farms studied. However, with one exception the 24-hour average daily concentrations of the virus were significantly below the experimentally estimated threshold for infection. A detailed model intercomparison established that, under stable atmospheric conditions, peak concentrations of virus up to two orders of magnitude higher might have been experienced for short periods, owing to fluctuations within the plume of virus, and model limitations. This finding would significantly reduce the apparent discrepancy between the experimentally estimated threshold for infection and the modelling results.

Patterns of spread and persistence of foot-and-mouth disease types A, O and Asia-1 in Turkey: a meta-population approach

Despite significant control efforts, foot-and-mouth disease (FMD) persists in Turkey, and new strains of serotypes A, O and Asia-1 are periodically reported to enter the country from the east. The status of FMD in Turkey is important regionally because the country forms a natural bridge between Asia where the disease is endemic, and Europe which has disease-free status. This study analysed spatial and temporal patterns of FMD occurrence in Turkey to explore factors associated with the disease's persistence and spread. Annual records of FMD distribution in Turkish provinces throughout 1990-2002, grouped by serotype (O, A and Asia 1), were analysed using geostatistical techniques to explore their spatial and temporal patterns. A meta-population model was used to test how disease status, expressed in terms of presence/absence, extinction, and colonization, and measured at the province level throughout the periods 1990-1996 and 1997 2002, could be predicted using province-level data on: ruminant livestock numbers; meat production-demand discrepancy (as a surrogate measure of animal and animal products marketing, i.e. long-distance contagion through the traffic of mainly live animals to urban centres); and the disease prevalence distribution as recorded for the previous year. A drastic overall reduction in FMD occurrence was observed from the period 1990-1996 to 1997-2002 when the disease was shown to retract into persistence islands. FMD occurrence was associated with host abundance, short distance contagion from adjacent provinces, and meat production-demand discrepancies. With FMD retracting into identified provinces, a shift in predictors of FMD occurrence was observed with a lower contribution of short-distance contagion, and a relatively higher association with meat production-demand discrepancies leading to live animal transport over long distances, and hence presenting opportunities for identifying critical-control points. The pattern of persistence differed according to serotype groups and is discussed in relation to their differential affinity to cattle and small ruminant hosts.

Linear hoof defects in sheep infected with foot-and-mouth disease

During the epidemic of foot-and-mouth disease (FMD) in The Netherlands in 2001, a sheep farm was identified that had been subclinically infected with the disease. The FMD virus genome was detected in 12 of 16 probang samples collected from the sheep and the virus was isolated from four of these samples. Linear defects were observed, 1 to 3 cm from the coronary band, in the hooves of several of the sheep. The defects were thought to have been caused by the FMD infection. It was thought that the distance of the defects from the coronary band might be an indication of the time since the animals had been infected. To determine the growth rate of the claws of sheep, the growth of the hoof horn of uninfected lambs and ewes was measured; in the lambs the growth rate was 0.44 mm per day and in the ewes it was 0.29 mm per day.

The foot-and-mouth disease epidemic in Dumfries and Galloway, 2001. 2: Serosurveillance, and efficiency and effectiveness of control procedures after the national ban on animal movements

After the foot-and-mouth disease (FMD) epidemic in Dumfries and Galloway in south-west Scotland in 2001, serosurveillance of sheep remaining in the 3 km radius Protection Zones around Infected Premises (IPS), and within a 10 km radius of IPS, revealed no evidence of infection. The epidemic was brought under control by a range of traditional techniques: slaughter of all animals on IPS and of veterinary-assessed Dangerous Contacts (DCS), movement restrictions, biosecurity, tracing of potential sources and spread of virus, and surveillance of At-Risk premises. Novel pre-emptive slaughter of FMD-susceptible animals on premises contiguous to IPS, and small ruminants and pigs on premises within 3 km of IPSs, commenced after the epidemic had peaked. Most of the traditional control procedures were undertaken quickly and with appropriate priority. Animals on IPS were usually slaughtered within one day of confirmation, and veterinary-assessed DCS within two days of confirmation of relevant IPS (a median of two days). The pre-emptive contiguous and 3 km culls took somewhat longer (medians of five and 17 days, respectively). IPS were most commonly identified as a result of reporting by farmers or their veterinarians (72 per cent of IPS); veterinary clinical patrols identified 16 per cent, while veterinary assessment of DCS and tracing each identified 5 per cent. No evidence of infection was found on any pre-emptively contiguously culled premises, and IPS were declared only on three 3 km cull premises. The time from estimated first lesion to end of slaughter on an IP was found, by regression analysis, to be a key component in effective control, manifested by a reduction in the estimated dissemination rate (EDR); there was little evidence that the intensity of contiguous culling affected the EDR. Patrols and serological surveillance of residual animals within 10 km of IPS, supported by more extensive evidence from elsewhere in the UK, suggested that cryptic infection in sheep was not widespread. Ultimately, there was insufficient evidence to support the effectiveness of 3 km pre-emptive culling as a control procedure.

Risk factors for herdsman-reported foot-and-mouth disease in the Adamawa Province of Cameroon

We analysed responses from 147 Fulani herdsmen to a questionnaire about cattle herd-level risk factors for foot-and-mouth disease (FMD) in the previous year. The study used a cross-sectional design with a stratified, two-stage random sample of cattle herds in the Adamawa Province of Cameroon. The questionnaire was pre-tested at a local cattle market before a final version was translated into Foulfoulde (the local Fulani dialect). Variables were screened using a univariable analysis and logistic multiple-regression models were developed in a forward-selection process. Fifty-eight percent (50-65; 90% CIs) of herdsmen reported FMD in their herd in the previous 12 months. Important risk factors for FMD in the previous 12 months included going on transhumance (OR=2.6), buying cattle from markets (OR=2.2), mixing of herds at watering points (OR=2.4), feeding cotton-seed cake (OR=3.3), buffalo near the herd (OR=2.2) and administrative division. For the subset of herds that went on transhumance, coming in contact with an FMDV-diseased herd while on transhumance was the strongest factor (OR=16).

Foot-and-mouth disease in camelids: a review

Foot-and-mouth disease (FMD) in South American camelids, in dromedaries and Bactrians is reviewed. Recent well-executed experimental studies in New World camels indicate that, although the llama and alpaca can be infected with FMD virus (FMDV) by direct contact, they are not very susceptible and do not pose a risk in transmitting FMD to susceptible animal species. They do not become FMDV carriers. Reports on FMD in dromedaries are, however, conflicting. Serological investigations in Africa and the United Arab Emirates (UAE) on thousands of camel sera were negative and experimental infections have been conducted on only a few dromedaries with one serotype and in one country. The design and execution of most of these experiments were poor and therefore the conclusions are questionable. From these investigations, it seems that dromedaries can contract the disease after experimental infection and through close contact with FMD diseased livestock, but do not present a risk in transmitting FMD to susceptible animals. They do not become FMDV carriers. Recent reports from Mongolia describe similar FMD lesions in Bactrian camels. However, so far no samples have tested positive for FMD. To clarify the situation in Bactrians, samples from suspected clinical cases should be tested because other viral vesicular diseases cannot be distinguished from FMD. Thus, further research on the epidemiology of FMD in camelids is necessary. This would include large-scale serological investigations and experimental infections with different FMD serotypes in connection with susceptible contact animals. The Office International des Epizooties (OIE) Code chapter on FMD includes camelids as being susceptible species to FMD, giving the impression that they are similar to cattle, sheep, goats and pigs in their potential involvement in the epidemiology of FMD. This is clearly not the case, and this issue should be re-addressed by the relevant authorities.

Early and Cost-Effective Identification of High Risk/Priority Control Areas in Foot-and-Mouth Disease Epidemics

Geo-referenced data from the 2001 Uruguayan foot-and-mouth disease (FMD) epidemic were explored to assess whether spatial analysis could lead to cost-benefit based policies. Four variables were analysed: (i) location and size of 4022 individual rural land parcels, of which 574 were infected over 60 days, (ii) animal density, (iii) percentage of dairy farms per county, and (iv) road density. Each variable was categorized into two to five classes (e.g. small/medium/large) and the proportion of cases per class reported at days 1-3 of the epidemic was compared with that reported at days 4-6. A higher proportion of cases was found at days 4-6 than at days 1-3 in areas with: small and medium size land parcels, high animal density, > 20% farms specialized in dairy production, and high road density (P < 0.03 for each). Each of these classes showed a greater proportion of cases at days 7-60 than the proportion of the total territory covered by each class's area (early case concentration ratios: 1.14-1.37). Land parcel clusters were indicated by Moran's I-test (P < 0.01). A new region was constructed by intersecting the four spatial classes associated with higher proportions of cases at days 4-6. At days 7-60, this region included 50.4% of all cases and represented 30.6% of the territory under study (final case concentration ratio: 1.65). The final area per case in this region was at least 33% lower and covered at least 45% less territory than any of the four single-variable approaches. Bio-statistical, multivariate spatial analysis of early cases may greatly increase the efficiency of epidemiologic policy.

Re-emergence of foot-and-mouth disease in Botswana

The re-emergence of foot-and-mouth disease (FMD) in Botswana is reported. The disease outbreak occurred in the Matsiloje Extension Area of Francistown veterinary district situated in the northeastern part of the country in an Office International des épízooties (OIE) recognized FMD free zone without vaccination. The disease affected cattle only and did not spillover into sheep and goats resident in the same extension area, as demonstrated by lack of seroconversion to FMD when tested. The virus isolate associated with the outbreak was identified as FMD virus; Southern African Territories (SAT) type SAT-2. The disease outbreak is discussed in relation to FMD outbreaks that have occurred previously within and outside Botswana.

Epidemiological investigations of the 2001 foot-and-mouth disease outbreak in Argentina

A total of 2126 herds, an attack rate of 0.82 per cent, were affected during an epidemic of foot-and-mouth disease in Argentina in 2001. The spatial and temporal distribution of the epidemic was investigated using nearest-neighbour and spatial scan tests and by estimating the frequency distributions of the times to intervention, and distances and times between outbreaks. The outbreaks were clustered and associated significantly (P<0.01) with herd density; 94 per cent were located in the Pampeana region, where the cattle population is concentrated, which had an attack rate of 1.4 per cent. The clustering results suggested that the virus had spread locally between outbreaks. Most of the outbreaks were separated by one day and the maximum distance between outbreaks was almost 2000 km, indicating that the infection spread rapidly over large distances. The index outbreak was detected more than 15 days after the primary outbreak, and restrictions on the movement of cattle were probably not enforced until about one month after infection occurred. As in other major epidemics, the period between the first outbreaks and the effective application of control strategies was probably crucial in determining the progress of the epidemic.

Quantitative estimates of the risk of new outbreaks of foot-and-mouth disease as a result of burning pyres

The risk of dispersing foot-and-mouth disease virus into the atmosphere, and spreading it to susceptible holdings as a result of burning large numbers of carcases together on open pyres, has been estimated for six selected pyres burned during the 2001 outbreak in the UK. The probability of an animal or holding becoming infected was dependent on the estimated level of exposure to the virus predicted from the concentrations of virus calculated by the Met Office, Bracknell. In general, the probability of infection per animal and per holding decreased as their distance from the pyre increased. In the case of two of the pyres, a holding under the pyre plumes became infected on a date consistent with when the pyre was lit. However, by calculating their estimated probability of infection from the pyres it was concluded that it was unlikely that in either case the pyre was the source of infection.

Serosurveillance of wild deer and wild boar after the epidemic of foot-and-mouth disease in the Netherlands in 2001

Blood samples from 140 wild deer and 208 wild boar shot in the aftermath of the epidemic of foot-and-mouth disease in The Netherlands in 2001 were examined for antibodies to foot-and-mouth disease virus. They were all negative.

Spatio-temporal epidemiology of foot-and-mouth disease in two counties of Great Britain in 2001

The spatial, temporal, and spatio-temporal features of the 2001 British foot-and-mouth disease epidemic in selected areas within the counties of Cumbria and Devon, which experienced the greatest incidence of disease, are described using hazard functions, extraction mapping and the space-time K-function. In Cumbria, the hazard of foot-and-mouth disease infection peaked at 2.8% in the week commencing 8 March 2001 and farm holdings in this area continued to be identified with disease to 12 September 2001. In contrast, peak infection hazard in Devon was 0.7% in the week commencing 15 March 2001 and eradication of the disease was achieved in this area by 31 May 2001. Persistence of the disease in Cumbria was consistent with: (1) many cattle holdings infected early in the epidemic (creating a high environmental viral load), and (2) a relatively large amount of medium-to-long-distance spread of the virus associated with seasonal farming activities-compounded to some extent by the movement of people and vehicles between disaggregated farm land parcels. The interaction of disease risk in Cumbria showed that premises remained infectious for longer throughout May, June and July, consistent with delays in disease detection during this period.

A stochastic-modeling evaluation of the foot-and-mouth-disease survey conducted after the outbreak in Miyazaki, Japan in 2000

When foot-and-mouth-disease (FMD) was identified in Miyazaki prefecture in March 2000, Japan conducted an intensive serological and clinical survey in the areas surrounding the index herd. As a result of the survey during the 21 days of the movement-restriction period, two infected herds were detected and destroyed; there were no other cases in the months that followed. To evaluate the survey used for screening the disease-control area and surveillance area, we estimated the herd-level sensitivity of the survey (HSe) through a spreadsheet model using Monte-Carlo methods. The Reed-Frost model was incorporated to simulate the spread of FMD within an infected herd. In the simulations, 4, 8 and 12 effective-contact scenarios during the 5-day period were examined. The estimated HSes of serological tests (HSeE) were 71.0, 75.3 and 76.3% under the 4, 8 and 12 contact scenarios, respectively. The sensitivity analysis showed that increasing the number of contacts beyond 12 did not improve HSeE, but increasing the number of sampled animals and delaying the dates of sampling did raise HSeEs. Small herd size in the outbreak area (>80% of herds have <20 animals) seems to have helped in maintaining HSeE relatively high, although the serological inspection was carried out before sero-positive animals had a chance to increase in infected herds. The estimated herd-level specificity of serological tests (HSpE) was 98.6%. This HSpE predicted 224 false-positive herds (5th percentile estimate was 200 and 95th percentile was 249), which proved close to the 232 false-positive herds actually observed. The combined-test herd-level sensitivity (serological and clinical inspections combined; CTHSe), averaged 85.5, 87.6 and 88.1% for the 4, 8 and 12 contact scenarios, respectively. Using these CTHSes, the calculated probability that no infected herd was overlooked by the survey was > or =62.5% under the most-conservative, four-contact scenario. The probability that no more than one infected herd was overlooked was > or =89.7%.

The pathogenesis and diagnosis of foot-and-mouth disease

The pathogenesis of foot-and-mouth disease (FMD) is reviewed, taking account of knowledge gained from field and experimental studies and embracing investigations at the level of the virus, the cell, the organ, the whole animal and the herd or flock. The review also addresses the immune response and the carrier state in FMD. Progress made in understanding the pathogenesis of the disease is highlighted in relation to developments in diagnosis and methods of control.

Epidemiology and control of an outbreak of foot-and-mouth disease in the Republic of Ireland in 2001

An outbreak of foot-and-mouth disease was confirmed in a flock of sheep on a farm in the Cooley peninsula, County Louth, on March 22, 2001. The virus was similar to other viruses of the serotype O PanAsian strain and virtually indistinguishable from other isolates from Northern Ireland and Great Britain. The epidemiological evidence suggested that infected sheep brought from Great Britain on February 19, 2001, were the source of the infection. The disease was eradicated by epidemiological investigation, serological testing and extensive culling.

Foot and mouth disease in Tanzania: an overview of its national status

The presence of foot-and-mouth disease (FMD) in Tanzania is a major obstacle to the development of the national livestock industry because of its adverse effects on livestock production and on trade of animals and animal products into lucrative export markets. FMD is endemic in Tanzania, the affected area is extensive and lack of funding makes eradication unrealistic. Uncontrolled livestock movements, the presence of large populations of wildlife in regular contacts with livestock, and the general lack of enthusiasm for FMD control among the key stakeholders, are some of the factors favouring the persistence of FMD in Tanzania. This review examines the epidemiology, dynamics and socio-economic significance of FMD in the national herd. Various control options available in Tanzanian context are also explored.

Clinical and laboratory investigations of five outbreaks of foot-and-mouth disease during the 2001 epidemic in the United Kingdom

Clinical and laboratory investigations of five outbreaks of foot-and-mouth disease (FMD) were made during the early stages of the 2001 epidemic in the UK. The first outbreak, confirmed on February 20, was at an abattoir in Essex which specialised in the processing of culled sows and boars. On February 23, the disease was confirmed at a pig farm in Northumberland which held cull sows and boars fed on waste food; the findings indicated that it was the first of the five premises to be infected. The disease had probably been present since early February, and it was the most likely origin of the epidemic. The other premises investigated were a waste food-fed cull sow/boar pig unit in Essex, approximately 30 km from the abattoir, which was probably infected at the same time or before the abattoir, a sheep and cattle farm approximately 6 km from the Northumberland pig farm, which was probably infected by airborne virus from it in the period immediately before February 13, and a sheep and cattle farm in Devon which had clinical disease from February 20 and was probably infected by sheep transported from Northumberland on February 13 which arrived on February 15.

The foot and mouth disease virus type O outbreak of 1992 is not related to vaccine strain (O/R2/75)

Vaccination is the only pragmatic approach to control foot and mouth disease in India. Strict quality control measures are essential to supply potent vaccine to the field application, in addition to monitoring the performance of the vaccine in the field. During the process of monitoring, an outbreak of FMD in vaccinated animals caused by type "O" virus in Tanjavur district of Tamil Nadu and a type "O" virus from unvaccinated herd of Karnataka were studied. Field isolates and vaccine virus were sequenced and analyzed. Data indicated that the virus from the outbreak in vaccinated cattle was a variant which could escape neutralization by antibodies against vaccine virus.

Likelihood of introducing selected exotic diseases to domestic swine in the continental United States of America through uncooked swill

To help policy makers determine the need for current regulations (which require cooking of swill prior to feeding to swine), an assessment of the likelihood of exposing domestic swine in the continental United States of America (USA) to selected foreign animal disease agents by feeding uncooked swill was carried out. The hazard was assumed to originate from contraband food items entering the USA and subsequently being discarded in household waste. Such food waste may be collected by licensed waste feeders and fed to swine. This study showed that, of the four diseases studied, the probability of exposure was highest for the classical swine fever (hog cholera) virus. The median annual likelihood of one or more contaminated loads of swill being fed to swine in the continental USA was estimated as follows: classical swine fever virus: 0.063, foot and mouth disease virus: 0.043, swine vesicular disease virus: 0.005, African swine fever virus: 0.005.

Foot-and-mouth disease. Challenge of cattle after multiple vaccinations

Four groups of six cattle were vaccinated from two to five times at 6 month intervals with two different trivalent FMD vaccines licensed in the given year. The FMDV type A strains in the vaccines designated A5F and A5B were closely related. Three months after the last vaccination the cattle were challenged by contact with animals inoculated with the original field strain A5B. The inoculated animals developed typical FMD symptoms with vesicles in the mouth and on the feet. Those cattle which had received vaccines that did not contain strain A5B also became severely sick, even after five vaccinations. Animals vaccinated twice with type B containing vaccine were also not completely protected. A safe protection can obviously only be achieved for fairly short periods of time if vaccine and challenge strain are homologous. It is proposed to change the rules of licensing, to speed up the procedure to vaccinate in cases of outbreaks. The need for further research, especially into improving vaccines, is stressed.

Pathogenesis of foot-and-mouth disease in swine, studied by in-situ hybridization

Eight 7-month-old pigs were inoculated intradermally with 10(3) plaque-forming units of foot-and-mouth disease virus, type O, and killed 24, 48, 72, or 96 h later. Numerous tissues from each animal were collected and examined histopathologically and by in-situ hybridization to determine the presence of virus and its correlation with lesion development. The probe for in-situ hybridization was a biotinylated 500-base negative-sense transcription product corresponding to a portion of the gene encoding polymerase. With this technique, virus was shown to be widely disseminated in all epidermal tissues, regardless of histologically apparent cellular disruption.

Field and laboratory analysis of an outbreak of foot and mouth disease in Bulgaria in 1991

In July 1991, an outbreak of foot and mouth disease (FMD) occurred near Stefan Karadjovo village in Boliarovo (south-east Bulgaria, close to the Turkish border). The virus isolated was identified in Bulgaria as serotype O and this was subsequently confirmed by the World Reference Laboratory for Foot and Mouth Disease in Pirbright (United Kingdom). Serological studies using bovine sera and monoclonal antibody analysis were made. In addition, the sequence of approximately 170 nucleotides at the 3' end of the 1D gene was determined for the field isolate and for vaccine strains used in Bulgaria. These were compared with other sequences of type O FMD viruses from outbreaks in the Middle East. Serum samples were taken from domestic animals in the region close to the outbreak and examined for anti-FMD virus antibodies to assess the extent (if any) of spread of the virus before or after the outbreak. No evidence of infection was found in these animals. The virus involved in the Bulgarian outbreak was antigenically similar to the O1 vaccine strains but probably did not originate from these strains. The virus was closely related genetically to a group of viruses isolated in the Middle East since 1987, suggesting that it may have been introduced into Bulgaria from an area in the Middle East by unidentified means.

Experimental infection of eland (Taurotrages oryx), sable antelope (Ozanna grandicomis) and buffalo (Syncerus caffer) with foot-and-mouth disease virus

The course of experimental infection of a type SAT 1 FMDV strain was studied in buffalo, sable antelope and eland following tongue inoculation and contact and has been compared with that in cattle. All species became infected, although disease was less severe in the game animals and larger amounts of virus were required to infect game animals than cattle. Neutralizing antibody titres were high and were maintained for an extended period in buffalo, sable antelope and eland. The carrier state was demonstrated in buffalo for the longest period. Cattle carried virus for up to 56 days. Virus persistence in sable antelope was transitory and did not occur in eland.

Foot-and-mouth disease--one of the remaining great plagues

Foot-and-mouth disease has been known for at least four centuries. The earliest reports of its occurrence are from Italy; it did not reach England until 1839. Its occurrence in South America was first described in 1871 and is probably linked to the movement of infected cattle from Europe to that part of the world. The earliest reports of the disease in Asia and Africa date from 1842 and 1892 respectively. The causal agent of the disease, a virus belonging to the family Picornaviridae, was discovered by Loeffler & Frosch in 1897; its antigenic diversity was described in the early 1920s. Seven serologically distinct types of the virus are now recognized, thus rendering the task of vaccination more complex, particularly as there is also considerable antigenic diversity within the serotypes. Nevertheless, good inactivated vaccines are available and, as demonstrated in western Europe over the last 30 years, these have proved to be extremely effective when applied prophylactically in efficiently organized programmes. The failure to control the disease adequately in Africa, Asia and South America can be partly explained by the more difficult local conditions and less-efficient veterinary services, together with the problems associated with maintaining the potency of a wet vaccine which is relatively unstable and requires storage at refrigerator temperatures. The potency of a vaccine is related to the mass of intact virus particles that it contains, and it is generally accepted that about 5 μg, as a single injection, will confer immunity against the severe challenge test which most national authorities demand. Studies of the structure of the virus have identified those parts of the particle which confer immunity when injected into susceptible host animals. Although the fine details have still to be determined, it appears that the major immunogenic site is contained within a sequence of 20 amino acids of one of the four structural proteins. At present, better methods for presenting the peptide so that it is more immunogenic are being sought ; the ultimate solution may depend on obtaining the three-dimensional structure of the immunogenic site by X-ray crystallography. The prospect of an indefinitely stable vaccine, which can be synthesized chemically and which could confer long-lasting immunity by a delayed-release mechanism, provides the impetus for further research in this field.

Association of foot-and-mouth disease virus induced RNA polymerase with host cell organelles

The localization of foot-and-mouth disease viral-induced RNA polymerase has been determined in situ and in partially fractionated cell components by using polymerase antisera tagged with either peroxidase or ferritin. Electron microscopic examination revealed the polymerase to be heavily concentrated on membranes of the smooth membranous vacuoles (SMV) which are newly formed during infection and which were previously shown to be the site where newly synthesized viral RNA appeared. Polymerase antigen was also seen to be associated with the endoplasmic reticulum (ER), the assumed site of original synthesis, and to a lesser extent with mitochondria and the Golgi apparatus. There was no significant polymerase attachment to nuclear and plasma membranes.

The role of sheep and goats in the epizootiology of foot-and-mouth disease in Kenya

The pathogenicity of two bovine field strains of virus for indigenous goats was examined in the laboratory. The goats failed to develop clinical disease or become virus carriers although the majority showed a definite immune response. A field survey in a foot-and-mouth disease enzootic area showed that the indigenous sheep and goat populations were frequently exposed to infection as evidenced by a high proportion of sero-positive animals but the incidence of virus carriers was very low in goats and no carriers were detected in sheep.

The pathogenicity of bovine strains of foot and mouth disease virus for impala and wildebeest

Impala (Aepyceros melampus) and wildebeest (Connochaetes taurinus) were infected with bovine strains of foot and mouth disease virus by intradermolingual inoculation. No clinical signs developed in the impala but mild atypical lesions developed in the tongues of the wildebeest with generalized spread to one foot in two of the eight animals exposed. All the impala but only some of the wildebeest developed viraemia. No virus could be isolated from any tissues in either species after the 7th day following virus inoculation. Immune response occurred in both species. A field survey revealed few animals of either species with significant antibody titers and no virus 'carriers' were found.