Comparison of different control strategies for foot-and-mouth disease: a study of the epidemics in Canada in 1951/52, Hampshire in 1967 and Northumberland in 1966

The measures used to control the epidemics of foot-and-mouth disease in Canada in 1951/52 (29 outbreaks) were compared with those used in the epidemic in Hampshire in 1967 (29 outbreaks). In both epidemics the disease spread more from premises where the disease was reported late and the imposition of quarantine or restrictions on infected premises was delayed. In Hampshire, area restrictions were imposed, susceptible livestock on infected premises and on premises in direct contact were slaughtered, and contacts were traced. In Canada, the initial diagnosis was vesicular stomatitis, no area restrictions were imposed, no tracing was carried out and the animals on infected premises were allowed to recover. However, apart from the disease's spread through infected meat and by unknown or airborne routes, it did not spread from infected premises once quarantine was imposed, partly owing to the low population density of livestock in the area. The effects of the slaughter of infected premises and direct contacts in the Fareham area of Hampshire in 1967 and in the Chathill area of Northumberland in 1966 were compared with what might have happened if, in addition, culling on contiguous premises or culling on premises within 3 km or emergency vaccination had been put into effect. The slaughter of cattle, sheep, goats and pigs on premises within 3 km two days after confirmation of the first outbreak would have resulted in fewer outbreaks and a shorter period to complete slaughter, but more animals would have been slaughtered. In the Chathill area, the slaughter of sheep, goats and pigs only on premises within 3 km two days after confirmation of the first outbreak would not have resulted in fewer outbreaks and more animals would have been slaughtered. Fewer premises and animals would have been slaughtered by a contiguous cull than by a 3 km cull but more than by the slaughter of infected premises and direct contacts. Emergency vaccination within 3 km, providing protection at four days (but not to animals already infected before the development of immunity), would have resulted in the fewest animals being slaughtered and could have reduced the number of outbreaks in the Fareham area by one and in the Chathill area by two or three. All the procedures would have had a greater effect the sooner they were introduced. However, with many foci of infection, priorities for action would have had to have been established. Earlier tracing of the last outbreak in the Fareham area could have shortened the Hampshire epidemic. Surveillance of a farm identified as at risk through animal movements and by the use of an airborne-prediction model could have eliminated the source of further outbreaks in the Chathill area.     

Airborne spread of foot-and-mouth disease in Saskatchewan, Canada, 1951-1952.

Farms affected with foot-and-mouth disease during the epidemic in Saskatchewan, in 1951-1952, for which the origin of virus was not known or uncertain, were studied to determine if infection could have been introduced by the airborne route. A short-range Gaussian plume dispersion model was used to estimate the concentration of virus downwind and the dose available for individual animals. The investigation suggested that a large virus source due to infected pigs in a feedlot in January 1952 could have been responsible for airborne dispersion northwestwards downwind to farms up to 20 km distant. Subsequent spread from these farms was to neighboring farms and was influenced by the local topography of a creek. The dispersion model could be used for predicting airborne spread if foot-and-mouth disease should occur.     

Airborne transmission of foot-and-mouth disease virus from Burnside Farm,Heddon-on-the-Wall,Northumberland, during the 2001 epidemic in the United Kingdom

The results of a detailed assessment of the atmospheric conditions when foot-and-mouth disease (FMD) virus was released from Burnside Farm, Heddon-on-the-Wall, Northumberland at the start of the 2001 epidemic in the UK are consistent with the hypothesis that the disease was spread to seven of the 12 farms in the immediate vicinity of the source by airborne virus, and airborne infection could not be ruled out for three other premises; the remaining two premises were unlikely to have been infected by airborne virus. The distances involved ranged from less than 1 km up to 9 km. One of the farms which was most probably infected by airborne virus from Burnside Farm was Prestwick Hall Farm, which is believed to have been key to the rapid spread of the disease throughout the country. In contrast, the results of detailed atmospheric modelling, based on a combination of clinical evidence from the field and laboratory experiments have shown that by assuming a relationship between the 24-hour average virus concentrations and subsequent infection, threshold infection levels were seldom reached at the farms close to Burnside Farm. However, significant short-term fluctuations in the concentration of virus can occur, and short-lived high concentrations may have increased the probability of infection and explain this discrepancy.     

Vesicular stomatitis.

Vesicular stomatitis is an infrequent yet important vesicular disease of cattle, horses, and swine. Periodic outbreaks of this disease in the United States have caused economic losses in cattle herds because of decreased production, movement restrictions, and trade embargoes. Vesicular stomatitis causes clinical signs indistinguishable from those of foot-and-mouth disease. It is of utmost importance that appropriate samples are collected from clinical cases of vesicular disease in cattle and swine so a rapid laboratory diagnosis can be made.     

Investigation of the possible spread of foot-and-mouth disease virus by the burning of animal carcases on open pyres

An atmospheric dispersion model was used to predict the airborne spread and concentrations of foot-and-mouth disease virus within the plumes generated by 11 pyres built to burn infected carcases during the epidemic of 2001 in the UK. On the basis of assumptions about the quantity of virus emitted during the three hours after the pyres were built and the threshold concentration of virus required to cause an infection in cattle, it was concluded that none of the disease breakdowns which occurred under the plumes was due to the spread of virus from the pyres.     

水疱性口炎研究进展

水疱性口炎(VS)是由水疱性口炎病毒(VSV)引起的人畜共患的重大动物疫病.VS病毒生态学复杂,易感动物较多,传播媒介种类广,病毒可在一定区域内长期存在.VSV主要呈嗜上皮性,大量流涎是家畜感染最重要的临床症状,其特征为口腔黏膜、乳房皮肤及蹄冠部皮肤出现水泡及糜烂,人感染后出现类似流感的症状.由于其临床症状与口蹄疫不易区别,发病时容易引起国际贸易恐慌,因此,对VS诊断防治的研究有着重要的社会经济和公共卫生意义.文章从分子生物学特征、流行病学、诊断和防控4个方面对水疱性口炎的研究进行了综述.     

An investigation of 11 outbreaks of foot-and-mouth disease in villages in northern Thailand

The results of investigations of 11 outbreaks of foot-and-mouth disease in villages in northern Thailand are described. The causative virus was Asia in one in seven outbreaks, Type O in two outbreaks and unknown in two outbreaks. The most probable sources of the outbreaks were co-mingling of cattle and/or buffalo with livestock from an infected neighbouring village (four) and recent introductions of infected cattle from a public livestock market (two) while the probable source could not be determined in five outbreaks. Attack rates in cattle and buffalo ranged from 0.28% to 50.9% but no pigs became sick during any of the outbreaks. Most outbreaks lasted 4 weeks or less. Adult cattle and buffalo were at higher risk of becoming a case when compared with work cattle. Beef cattle were at higher risk than buffalo and adult cattle and buffalo were at higher risk than calves less than 1 year of age. There was significant clustering of cases within households. Serological investigations indicated that many unaffected animals were probably not exposed to virus during the outbreaks. We concluded that close contact between animals was the main method of spread and that differences in attack rates between animal classes reflected differences in animal management. We further concluded that simple quarantine of early cases during outbreaks is likely to be effective in reducing spread within and between villages.     

Microarray-based detection of viruses causing vesicular or vesicular-like lesions in livestock animals

Definitive diagnosis of vesicular or vesicular-like lesions in livestock animals presents challenges both for veterinary clinicians and diagnostic laboratories. It is often impossible to diagnose the causative disease agent on a clinical basis alone and difficult to collect ample vesicular epithelium samples. Due to restrictions of time and sample size, once laboratory tests have ruled out foot-and-mouth disease, vesicular stomatitis and swine vesicular disease a definitive diagnosis may remain elusive. With the ability to test a small quantity of sample for a large number of pathogens simultaneously, DNA microarrays represent a potential solution to this problem. This study describes the application of a long oligonucleotide microarray assay to the identification of viruses known to cause vesicular or vesicular-like lesions in livestock animals. Eighteen virus isolates from cell culture were successfully identified to genus level, including representatives of each foot-and-mouth disease virus serotype, two species of vesicular stomatitis virus (VSV), swine vesicular disease virus, vesicular exanthema of swine virus (VESV), bovine herpesvirus 1, orf virus, pseudocowpox virus, bluetongue virus serotype 1 and bovine viral diarrhoea virus 1. VSV and VESV were also identified in vesicular epithelium samples, with varying levels of sensitivity. The results indicate that with further development this microarray assay could be a valuable tool for the diagnosis of vesicular and vesicular-like diseases.     

Modeling the spread and control of foot-and-mouth disease in Pennsylvania following its discovery and options for control

In this paper, we simulate outbreaks of foot-and-mouth disease in the Commonwealth of Pennsylvania, USA - after the introduction of a state-wide movement ban - as they might unfold in the presence of mitigation strategies. We have adapted a model previously used to investigate FMD control policies in the UK to examine the potential for disease spread given an infection seeded in each county in Pennsylvania. The results are highly dependent upon the county of introduction and the spatial scale of transmission. Should the transmission kernel be identical to that for the UK, the epidemic impact is limited to fewer than 20 premises, regardless of the county of introduction. However, for wider kernels where infection can spread further, outbreaks seeded in or near the county with highest density of premises and animals result in large epidemics (>150 premises). Ring culling and vaccination reduce epidemic size, with the optimal radius of the rings being dependent upon the county of introduction. Should the kernel width exceed a given county-dependent threshold, ring culling is unable to control the epidemic. We find that a vaccinate-to-live policy is generally preferred to ring culling (in terms of reducing the overall number of premises culled), indicating that well-targeted control can dramatically reduce the risk of large scale outbreaks of foot-and-mouth disease occurring in Pennsylvania.     

The epidemiology of foot-and-mouth disease: implications for New Zealand

Foot-and-mouth disease is an acute, highly communicable disease affecting cloven-hoofed animals, both domesticated and wild. It may well be the most contagious disease known in the animal kingdom. The key features that contribute to this include its ability to gain entry and initiate infection through a variety of sites, the small infective dose, the short incubation period, the release of virus before the onset of clinical signs, the massive quantities of virus excreted from infected animals, its ability to spread large distances due to airborne dispersal, and the persistence of the virus in the environment. These features, plus the ability of the virus to be disseminated through the movements of animals, animal products, people, and plant and equipment makes the disease very difficult to control. New Zealand has never experienced a foot-and-mouth disease epidemic, and the economic consequences of an outbreak would be disastrous, due to the eradication costs, the loss of productivity and the impact on the export of animals and animal products. The smuggling of meat products, embryos or semen into the country are perceived as the most likely ways in which the disease could be introduced. The New Zealand Ministry of Agriculture and Fisheries therefore operates a two-tier system of defense against foot-and-mouth disease. The first tier involves border protection through stringent import controls to prevent the entry of infectious material. If this barrier is breached, an emergency response programme is activated, involving a stamping-out eradication strategy. This paper attempts to draw on overseas historical outbreak experiences and research findings to gain insights into the epidemiology of foot-and-mouth disease as it would relate to New Zealand.     

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.     

Long distance transport of foot-and-mouth disease virus over the sea

The conditions required for the transport of foot-and-mouth disease (FMD) virus in the atmosphere over long distances and in sufficient concentrations to cause infection in exposed animals are described. Using these factors a series of 23 outbreaks of FMD in Europe, where the original outbreaks were separated from later outbreaks by sea passage, have been investigated. The findings obtained support the hypothesis that under certain conditions the airborne transmission of FMD over a long sea passage is possible.     

An experimental infection in pigs using a foot-and-mouth disease virus isolated from the 2010 epidemic in Japan

In this study, we carried out an experimental infection in pigs using a foot-and-mouth disease virus isolated from the 2010 epidemic in Japan to analyze the clinical manifestation, antibody response and virus shedding patterns in pigs. We found that the virus was virulent in pigs, producing a synchronous disease in the inoculated pigs and efficient spread to direct contact pigs. These results are useful for epidemiologically investigating the 2010 epidemic in Japan and improving the measures for controlling possible future FMD outbreaks in Japan or elsewhere.     

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.     

Temporal-spatial epidemiology of foot-and-mouth disease outbreaks in Mongolia, 2000 – 2002

Prior to 2000, foot-and-mouth disease (FMD) had not been observed in Mongolia since 1973; however, between April 2000 and July 2002, Mongolia reported 44 FMD outbreaks that affected cattle, sheep, goats, and camels. The objectives of this study were to describe the distributions of the 44 reported FMD outbreaks in Mongolia and to assess their spatial clustering and directions of movement. Official reports were collected to obtain the number and species of animals both affected and at risk, and the date and geographical coordinates of each outbreak. Significant global and local spatial clusters of reported FMD outbreaks were identified. Disease spread during the second epidemic moved 76° northeast and the spread of the disease during the third epidemic moved 110° northwest. FMD outbreaks were clustered intensely close to other FMD-positive counties. These findings can be used in the future to help plan prevention and control measures in high risk areas.     

Serologic survey of viral antibodies in the Peruvian alpaca (Lama pacos)

Sera from more than 100 alpacas (Lama pacos) from the Peruvian southern sierra were examined for antibodies to 8 viruses known to infect other domestic animals. On the basis of these serologic findings and previously published serologic or clinical data, it is now known that the alpaca can be infected with the following viruses: parainfluenza-3, bovine respiratory syncytial virus, bovine herpesvirus-1, bluetongue virus, border disease virus, influenza A virus, rotavirus, rabies virus, vesicular stomatitis virus, foot-and-mouth disease virus, and contagious ecthyma virus.     

Reanalysis of the start of the UK 1967 to 1968 foot-and-mouth disease epidemic to calculate airborne transmission probabilities

The aims of this study were to statistically reassess the likelihood that windborne spread of foot-and-mouth disease (FMD) virus (FMDV) occurred at the start of the UK 1967 to 1968 FMD epidemic at Oswestry, Shropshire, and to derive dose-response probability of infection curves for farms exposed to airborne FMDV. To enable this, data on all farms present in 1967 in the parishes near Oswestry were assembled. Cases were infected premises whose date of appearance of first clinical signs was within 14 days of the depopulation of the index farm. Logistic regression was used to evaluate the association between infection status and distance and direction from the index farm. The UK Met Office's NAME atmospheric dispersion model (ADM) was used to generate plumes for each day that FMDV was excreted from the index farm based on actual historical weather records from October 1967. Daily airborne FMDV exposure rates for all farms in the study area were calculated using a geographical information system. Probit analyses were used to calculate dose-response probability of infection curves to FMDV, using relative exposure rates on case and control farms. Both the logistic regression and probit analyses gave strong statistical support to the hypothesis that airborne spread occurred. There was some evidence that incubation period was inversely proportional to the exposure rate.     

Molecular characterization of foot-and-mouth disease virus isolated from ruminants in Taiwan in 1999-2000

In 1999, 10 sporadic outbreaks of cattle foot-and-mouth disease (FMD) occurred in Taiwan. By the time, infection was limited to the Chinese yellow cattle (a native species of beef cattle in Mainland China), which did not develop vesicular lesions under field conditions. Five viruses isolates obtained from individual farms were confirmed to be the serotype O FMD virus (O/Taiwan/1999). During January-February 2000, however, this virus has spread to dairy cattle and goat herds, causing severe mortality in goat kids and vesicular lesions in dairy cattle. Partial nucleotide sequence of the capsid coding gene 1D (VP1) was determined for the virus isolates obtained in this study. Phylogenetic analysis of the VP1 sequences indicated that the O/Taiwan/1999 viruses shared 95-97% similarities to the virus strains isolated from the Middle East and India. The species susceptibility of the O/Taiwan/1999 virus was experimentally studied in several species of susceptible animals, showing that the virus did cause generalized lesions in dairy cattle and pigs, however, it would not cause vesicular lesions on the Chinese yellow cattle and the adult goats. These studies suggested that the O/Taiwan/1999 virus was a novel FMD virus of Taiwan and it presented various levels of susceptibility in cattle species.     

Vesicular stomatitis and other vesicular, erosive, and ulcerative diseases of horses.

Physical trauma, dietary factors, certain toxins, immune mediated disorders, and vesicular stomatitis virus (VSV) infection are known causes of stomatitis in horses. There is evidence that some outbreaks of equine stomatitis are caused by as yet unidentified infectious agents. It remains to be determined whether stomatitis is an emerging equine infectious disease, or if the increase in reported cases is simply the result of greater public awareness as a consequence of widespread outbreaks of VSV in the southwestern United States in recent years. Focused laboratory and epidemiological studies are necessary to more adequately define non-VS related infectious and noninfectious causes of equine stomatitis.     

Effect of strain and serotype of vesicular stomatitis virus on viral shedding, vesicular lesion development, and contact transmission in pigs

OBJECTIVE: To determine whether pigs can be infected with strains of vesicular stomatitis virus New Jersey (VSV-NJ) and vesicular stomatitis virus Indiana (VSV-I) isolated during recent vesicular stomatitis outbreaks that primarily involved horses in the western United States and determine the potential for these viruses to be transmitted by contact. ANIMALS: 128 pigs. PROCEDURE: Pigs were challenged with VSV-NJ or VSV-I from the 1995 and 1997 outbreaks of vesicular stomatitis in the western United States, respectively, or with VSV-NJ (OS) associated with vesicular stomatitis in feral pigs on Ossabaw Island, Ga. Pigs (3/group) were inoculated with each virus via 3 routes and evaluated for viral shedding, seroconversion, and the development of vesicular lesions. In another experiment, the potential for contact transmission of each virus from experimentally infected to na?ve pigs was evaluated. RESULTS: Infection of pigs was achieved for all 3 viruses as determined by virus isolation and detection of seroconversion. In inoculated pigs, all 3 viruses were isolated from multiple swab samples at concentrations sufficient to infect other pigs. However, compared with results obtained with the 2 VSV-NJ strains, viral titers associated with VSV-I were low and the duration of virus shedding was reduced. Results from the contact transmission trials were consistent with these results; virus transmission was detected most frequently with the VSV-NJ strains. CONCLUSIONS AND CLINICAL RELEVANCE: Pigs can be infected with VSV-NJ and VSV-I. Differences in the extent of viral shedding and potential for contact transmission were apparent between serotypes but not between the VSV-NJ strains investigated.