Some observations on the diagnosis of foot and mouth disease

Extract

Although in most instances the clinical diagnosis of Foot and Mouth disease presents no great difficulty, one's mental state is generally somewhat tense when on the way to deal with a suspected case. So much depends on the decision—a nation awaits the verdict! Hence the spurious glamour of foot and mouth disease, which would ordinarily be considered one of the most easily recognized of infectious diseases.     

Factors associated with the clinical diagnosis of foot and mouth disease during the 2001 epidemic in the UK

The purpose of this investigation was to identify factors associated with the clinical diagnosis of foot and mouth disease during the 2001 epidemic in the United Kingdom. Using logistic regression, we compared: (1) reports of suspect disease that resulted in the declaration of FMD to reports that did not, and (2) laboratory-positive cases to laboratory-negative cases. From 6,801 reports of suspect disease, 2,026 cases of FMD were identified. Suspect cases were more likely to become clinical cases if: (1) the report originated from the disease control authorities ('active surveillance') rather than the public, usually farmers ('passive surveillance'); (2) cattle were the species suspected of disease, as opposed to sheep; (3) the report was filed during the peak of the epidemic; (4) the reporting premises was within 3 km of an FMD case detected within the previous 2 weeks; or (5) the report originated from certain local disease control centres. There were significant two-way interactions between: type of surveillance and species suspected of disease, type of surveillance and proximity of other infected premises, species suspected and time in the epidemic, and time in the epidemic and proximity of other infected premises. Clinical cases were more likely to be laboratory positive if: (1) they were found by passive versus active surveillance, (2) cattle were suspected of disease (versus sheep), (3) oldest lesions were less than 3 days, (4) the report was filed at any time other than the peak of the epidemic, or (5) the report originated from certain local disease control centres. Significant two-way interactions were found between: type of surveillance and species suspected of disease, and type of surveillance and time in the epidemic.     

Clinical signs and differential diagnosis of foot and mouth disease in pigs

FMD in pigs is primarily a foot disease. It is dominated by rather painful formation of vesicles in the epidermis of the feet (coronary band, interdigital clefts, bulbs) combined with severe lameness. Complications will be seen as detachment of the hoof and secondary infection of disrupted aphthae which may cause purulent arthritis of the pedal joint. Concerning differential diagnosis are to be considered all cases of acute lameness, vesicle-formation as typical lesions of exudative epidermites of pemphigus in the course of infections with S. hyicus or S. aureus as well as degenerative changes after selenium-intoxication, specially near the coronary band, sometimes linked with exungulation.     

Clinical picture and differential diagnosis of foot and mouth disease in cattle

Foot-and-mouth disease (FMD) in cattle is characterized by the formation of vesicles and erosions in the mouth, teats and feet. Despite extremely high morbidity, mortality in adults is usually very low, however up to 50% of calves dies due to cardiac involvement or secondary infections. This paper describes the signs of FMD in cattle as well as those of other diseases which causes similar lesions in this species.     

Diagnosis of foot and mouth disease

Because foot-and-mouth disease has the potential for an explosive spread, instant and reliable diagnosis is of special importance. In this article the clinical examination, types and shipment of samples as well as the current methods of laboratory diagnosis by detection of FMD-virus, antigen, nucleic acid and antibodies are reviewed. Special emphasis is laid on the differentiation between vaccinated and infected animals, in respect to conventional as well as novel vaccines.     

A vesiculo-bullous disease in pigs resembling foot and mouth disease. I. Field cases

Eleven incidents of bullae and vesicles on the snouts and less frequently the feet of white-skinned pigs on seven farms are described. Bullous and vesicular lesions up to 5 cm in diameter and containing clotted gelatinous fluid were located on the dorsal aspect of the snout, behind the flange. Lesions ruptured, became ulcerated, developed scabs and healed within three weeks. There was no transmission to other pigs or ruminants. The condition was associated with contact with green vegetable material containing parsnips (Pastinaca sativa) or celery (Apium graveolens), followed by exposure to periods of extended sunshine. Parsnips and celery are known to contain furocoumarins, potent phototoxic compounds. It is suggested that absorption of furocoumarins on the skin of the snout and feet after contact with parsnips and celery and exposure to ultraviolet light caused the lesions in the cases reported. It is postulated that a similar condition may have been responsible for national foot and mouth disease scares in pigs at Warkworth and Temuka in New Zealand and at Legana in Tasmania.     

The impact of seasonal variability in wildlife populations on the predicted spread of foot and mouth disease

Modeling potential disease spread in wildlife populations is important for predicting, responding to and recovering from a foreign animal disease incursion such as foot and mouth disease (FMD). We conducted a series of simulation experiments to determine how seasonal estimates of the spatial distribution of white-tailed deer impact the predicted magnitude and distribution of potential FMD outbreaks. Outbreaks were simulated in a study area comprising two distinct ecoregions in South Texas, USA, using a susceptible-latent-infectious-resistant geographic automata model (Sirca). Seasonal deer distributions were estimated by spatial autoregressive lag models and the normalized difference vegetation index. Significant (P < 0.0001) differences in both the median predicted number of deer infected and number of herds infected were found both between seasons and between ecoregions. Larger outbreaks occurred in winter within the higher deer-density ecoregion, whereas larger outbreaks occurred in summer and fall within the lower deer-density ecoregion. Results of this simulation study suggest that the outcome of an FMD incursion in a population of wildlife would depend on the density of the population infected and when during the year the incursion occurs. It is likely that such effects would be seen for FMD incursions in other regions and countries, and for other diseases, in cases in which a potential wildlife reservoir exists. Study findings indicate that the design of a mitigation strategy needs to take into account population and seasonal characteristics.     

A vesiculo-bullous disease in pigs resembling foot and mouth disease. II. Experimental reproduction of the lesion

Vesiculo-bullous dermatitis of pigs characterised by presence of vesicles and bullae on the snout and feet of white skinned pigs was reproduced experimentally. Leaves of parsnips (Pastinaca sativa), or celery (Apium graveolens) infected with the fungus Sclerotinia sclerotiorum were fed or rubbed on the snouts and feet of white skinned pigs. Pigs were then exposed to sunlight or to UV light of intensity approximately 212 m W/M2 at a wavelength 340-360 nm for eight hours per day until vesicles developed. All treated pigs developed lesions on the snouts, and less frequently on the feet. Lesions were characterised by the appearance of erythema at 24 hours after treatment. Vesicles developed at 48 hours and became maximal by 72 hours. Pigs treated with plant material without exposure to UV light or exposed to UV light without contact with plant material did not develop lesions. The experimental lesions closely resemble those observed in several field cases in 1984 and 1985 in New Zealand and to lesions present in three well publicized foot and mouth disease scares at Warkworth, and Temuka in New Zealand and Legana in Tasmania.     

History of the control of foot and mouth disease

From the many existing documents on the history of foot and mouth disease, it is possible to describe the practical measures adopted for disease surveillance and control from ancient times until the 20th century.

Surveillance was based on diagnosis or post-mortem examination, and also on knowledge of the conditions under which infection occurred: aetiology, pathogenesis, mode of infection, susceptible species, virulent material, etc. The historical facts are assembled and compared, with comments on each of these points.

Control was based upon the application of isolation, then slaughter or aphtisation, then vaccination. A study of these various procedures makes it possible to compare their efficacy.

Résumé

D'après les nombreux documents existant sur l'histoire de la fièvre aphteuse il est possible de décrire les mesures adoptées pour suivre l'évolution de la maladie et la maîtriser, depuis l'Antiquité jusqu'au XXème siècle.

La surveillance de la maladie était fondée sur le diagnostic clinique ou l'examen des lésions, mais aussi sur la connaissance des condition de l'infection: étiologie, pathogénie, mode de transmission du contage, matières virulentes, etc. Les faits historiques concernant ces différents points sont rassemblés, comparés et commentés.

La maîtrise de la fièvre aphteuse a été assurée soit par des mesures d'isolement, puis d'abattage sanitaire, soit par des opérations d'aphtisation puis de vaccination. L'étude de ces différentes stratégies permet de comparer leur efficacité respective.     

Characteristics of foot and mouth disease virus in Taiwan

Since March 1997 two strains of foot and mouth disease (FMD) virus have found their way into Taiwan, causing severe outbreaks in pigs and in Chinese yellow cattle. Outbreaks occurred in March 1997 were caused by a pig-adapted virus strain (O/Taiwan/97) which did not infect other species of cloven-hoofed animals by natural route. The epidemic spread over the whole region of Taiwan within two months and the aftermath was 6,147 pig farms infected and 3,850,746 pigs destroyed. In June 1999, the second strain of FMD virus (O/Taiwan/99) was isolated from the Chinese yellow cattle in the Kinmen Prefecture and in the western part of Taiwan. By the end of 1999, Chinese yellow cattle were the only species infected and those infected cattle did not develop pathological lesions. Seroconversions of serum neutralization antibody and on non-structural protein (NSP) antibodies were the best indicators for infection in non-vaccinated herds. The infected animals, however, excreted infectious levels of virus to infect new hosts. Based on the detection of the specific antibody to FMD virus, and virus isolation from oesophageal-pharyngeal (OP) fluid samples, ten herds of Chinese yellow cattle located in Kinmen and Taiwan were declared to have been infected. During the period of January to March 2000, however, five outbreaks caused by FMD virus similar to the O/Taiwan/99 virus occurred in four prefectures of Taiwan. The infected species included goats, Chinese yellow cattle and dairy cattle. Those outbreaks have caused high mortality in goat kids under two weeks old and also developed typical clinical signs of infection in dairy cattle.     

一例牛口蹄疫疫苗免疫过敏反应的诊治

口蹄疫是由口蹄疫病毒引起的偶蹄动物的一种急性、热性、高度接触性一类传染病,具有发病急、蔓延快、传播广、危害大等特点。我国对本病采取了100%注射疫苗强制免疫的措施,有效地控制了本病的发生及蔓延。然而在注苗免疫过程中,因个体差异等原因,个别家畜往往出现不同程度的过敏反应,有时因救治不及时或治疗方法不当造成死亡,给养殖户带来一定的经济损失,也影响了防疫工作的有效推进。文章通过一例牛口蹄疫免疫过敏病例的救治,介绍了牛在接种口蹄疫疫苗后可能出现的应激反应,并提出了解救措施,为及时、有效处理口蹄疫疫苗应激反应提供参考。     

Brazilian foot and mouth disease status and meat exportation to the European Union

The aim of this study was to define the differences between the Brazilian states that export and do not export meat to the European Union (EU) and to identify the variables that are important to meet the export requirements. Infrastructure and computerization of the control of animal transit in Brazil that impact on regional health status were evaluated and linked to other variables such as status for foot and mouth disease (FMD) and qualification to export meat to EU. Variables related to transit control of bovines implemented by the state agencies of animal health and inspection in each Brazilian state were evaluated. Using a discriminant analysis, four variables were selected that explained the variation between Brazilian states that were “free” and “not free” of FMD while another four were selected to explain the variation between the zones “approved” and “not approved” to export meat to the EU, including number of official veterinarians, total transit of bovines and buffaloes, total number of animal transit certificates issued for bovine and buffaloes at the state or zone level, and total number of municipalities in the state or zone. It was possible to correctly discriminate between “free” and “not free” FMD states or zones. Variables related to animal transit are important in assessing the state for the classification of animal health situation and for EU approval for the exportation of meat.