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An assessment of the current status of foot-and-mouth disease in Nigeria.

Foot-and-mouth disease has been widespread throughout the country in recent years. The disease occurs mainly in cattle though spillover of infections has been observed in sheep and pigs. Virus types A, SAT 2 and SAT 1 are the usual cause of outbreaks. The present field control method is a 6-monthly vaccination schedulae for animals in government ranches, the few semi-commercial ranches and piggeries as well as for other valuable animals and exotic animals of high production quality. Arrangements are under way to institute a strict and more comprehensive control programme against the disease in view of the envisaged expansion of livestock development projects and improved zoo-sanitary status projected for our 3rd National Livestock Development Plan. A national policy of a barrier and frontier vaccination programme supplemented with strategic vaccinations in vulnerable foci is here recommended and discussed on the basis of a survey on the present status of the disease.

Animals↗

[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.

Age Factors↗

[Survey of foot and mouth disease in France].

The Foot and Mouth disease is considered a relatively mild disease in susceptible animals but it has a considerable economical impact in France and worldwide due to the huge economical losses that it generates. A system for the prevention of the disease was developed thirty years ago and has since been continuously improved. The current system for the prevention of FMD is based on training and information of all those involved in the surveillance of susceptible animals, over all the national territory, and on the control of imported animals and animal products. This system, developed in close collaboration with the European Commission and the other EU member states, allows control measures to be implemented almost instantaneously, if a case is suspected to avoid spreading of the disease.

Animal Diseases↗

The role of management segregations in controlling intra-herd foot-and-mouth disease.

Transmission of foot-and-mouth disease virus (FMDV) by aerosol spread can occur over considerable distances. However, this is less effective in hot, dry environmental conditions, and a detailed study of an outbreak within a large dairy herd in Saudi Arabia has shown that contact spread is the main mode of transmission within a herd: both physical and spatial barriers curtailed the course of disease across the farm. Hence, the speed and path of an outbreak can be altered by changing the positioning of spatial or physical barriers. Extending the distances between pens, increasing the number of farm pens, decreasing the number of animals within the pens, and placing pens of well-protected stock between those of susceptible stock, can all contribute to the control of FMD involving contact and short-distance aerosol spread. Such management techniques offer a cost-effective supplement to control by vaccination.

Animal Husbandry↗

Simulated airborne spread of Aujeszky's disease and foot-and-mouth disease.

The atmospheric dispersion of virus was simulated using a computer model which had been developed for predicting the dispersion of toxic gases from chemical engineering plants. The results were compared with data from four outbreaks in which virus was believed to have been transported by air: two outbreaks of foot-and-mouth disease in the United Kingdom in 1967 and outbreaks of Aujeszky's disease in Yorkshire in 1981 to 1982 and Indiana in 1988. There was relatively good agreement with most of these data. The paper shows that the model could be useful in an emergency because the risk of virus spread could be predicted in real time.

Air Microbiology↗

Comparative studies of the capsid precursor polypeptide P1 and the capsid protein VP1 cDNA vectors for DNA vaccination against foot-and-mouth disease virus.

BACKGROUND: Foot-and-mouth disease virus (FMDV) causes a severe livestock disease, and the virus is an interesting target for virology and vaccine studies. MATERIALS AND METHODS: Here we evaluated comparatively three different viral antigen-encoding DNA sequences, delivered via two physical means (i.e., gene gun delivery into skin and electroporation delivery into muscle), for naked DNA-mediated vaccination in a mouse system. RESULTS: Both methods gave similar results, demonstrating commonality of the observed DNA vaccine effects. Immunization with a cDNA vector expressing the major viral antigen (VP1) alone routinely failed to induce the production of anti-VP1 or neutralizing antibodies in test mice. As a second approach, the plasmid L-VP1 that produces a transgenic membrane-anchored VP1 protein elicited a strong antibody response, but all test mice failed in the FMDV challenge experiment. In contrast, for mice immunized with the viral capsid precursor protein (P1) cDNA expression vector, both neutralizing antibodies and 80-100% protection in test mice were detected. CONCLUSIONS: This strategy of using the whole capsid precursor protein P1 cDNA for vaccination, intentionally without the use of virus-specific protease or other encoding genes for safety reasons, may thus be employed as a relevant experimental system for induction or upgrading of effective neutralizing antibody response, and as a convenient surrogate test system for DNA vaccination studies of FMDV and presumably other viral diseases.

Animals↗

Further studies to quantify the dose of natural aerosols of foot-and-mouth disease virus for pigs.

Foot-and-mouth disease virus (FMDV) can be spread by a variety of mechanisms, including wind. Simulation models, developed to predict the risk of airborne spread, have played an important part in decision making in some outbreaks. The amount of airborne virus excreted as well as the minimal infectious dose (MID) of FMDV for different species are important determinants of airborne spread. The objective of this study was to obtain data for the O1 Lausanne, O SKR 2000 and O UKG 2001 strains of FMDV to enhance the capability of such models. Pigs were exposed to naturally generated aerosols of the three strains using an experimental design which delivered high doses of the two strains O1 Lausanne and O SKR 2000 over a short period, or of the O UKG 2001 strain over an extended period. The average excretion of the O1 Lausanne strain was 10(6.4) TCID50 per pig per hour. The excretion of the O SKR 2000 strain averaged 10(5.8) and the O UKG 2001 strain 10(6.1) TCID per pig per 24 h. The results show that the previous estimate of 'above' 800 TCID50 as the MID50 for the O1 Lausanne strain is a considerable under-estimate and that the real dose may be as high as 6000 TCID50. A dose of around 650 TCID50 of the O SKR 2000 strain failed to infect any pigs. Thus, the aerosol MID50 for pigs for this isolate is at least 1000 TCID50 and likely to be as high or higher than the O1 Lausanne strain. The exposure of pairs of recipient pigs kept physically separated from donor pigs in a series of rooms to aerosol exposure doses of the O UKG 2001 strain of around 50 TCID50 per min for 24-48 h failed to infect any of eight pigs. Thus, the present experiment confirms our previous findings that pigs, compared to cattle and sheep, are relatively resistant to infection with airborne FMDV.

Aerosols↗

Production and characterization of two serotype independent monoclonal antibodies against foot-and-mouth disease virus.

Two foot-and-mouth disease virus (FMDV) monoclonal antibodies (mAbs) were produced from mice immunized with either FMDV serotype A, subunit (12S) or FMDV serotype O, whole virus (140S). Both mAbs (F1412SA and F21140SO) recognized all seven serotypes of FMDV in a double antibody sandwich (DAS) ELISA, suggesting that the binding epitopes of the two mAbs are conserved between serotypes. These mAbs are IgG1 isotype and contain kappa light chains. In order to define the mAb binding epitopes, the reactivity of these mAbs against trypsin-treated and denatured FMDV were examined using an indirect ELISA. The binding site of the mAb, F1412SA is trypsin sensitive and the epitope is linear. Both ELISA and Western blot results suggested that the polypeptide VP2 contributed to the immunodominant site. This mAb showed reactivity to VP2 peptide (DKKTEETTILEDRIL). The mAb, F21140SO, recognized an epitope which is trypsin resistant and discontinuous. This mAb binding to FMDV is dependent on conformational structures of intact viral (140S) or subunit (12S) particle, since it failed to recognize any viral protein in Western blot. This conformational and highly conserved epitope is the first identified epitope among all seven FMDV serotypes. Because the use of mAbs increases the specificity, accuracy and efficiency of diagnostic tests compared to polyclonal antisera, these two mAbs with different specificities are suitable for type-independent diagnosis of FMDV, such as DAS ELISA, or could be adapted to immuno-chromatographic or flow-through rapid test.

Amino Acid Sequence↗

Use of confocal immunofluorescence microscopy to localize viral nonstructural proteins and potential sites of replication in pigs experimentally infected with foot-and-mouth disease virus.

Replication of foot-and-mouth disease virus in infected pig epithelium has been studied by immunofluorescence labeling of the viral nonstructural protein 3ABC and confocal microscopy. The results were correlated with viral RNA copy numbers in tissue samples from adjacent sites determined by reverse transcription-PCR (RT-PCR). Lesion formation was seen in the tongues and coronary band epithelia of infected pigs 2 days after infection. Viral replication was observed in cells of the epithelium of the tongue and coronary band but not in the associated stromal cells. Infected epithelial cells were present in the stratum spinosum, away from the lesion, with small lesions formed above the basement membrane. Viral replication was markedly reduced in tongue epithelium by day 3 postinfection but remained apparent in the coronary band tissue up to 5 days postinfection. These results were confirmed by the RNA copy number determined by RT-PCR.

Animals↗

Anti-3AB antibodies in the Chinese yellow cattle infected by the O/Taiwan/99 foot-and-mouth disease virus.

The O/Taiwan/99 foot-and-mouth disease virus (FMDV), a South Asian topotype of serotype O, was introduced into Taiwan in 1999. The Chinese yellow cattle infected by the virus did not develop clinical lesions under experimental and field conditions. A blocking enzyme-linked immunosorbent assay (ELISA) kit with the 3AB antigen, a polypeptide of FMDV non-structural (NS) proteins, was used to evaluate the development and duration of anti-3AB antibodies, proving active viral replication, in the Chinese yellow cattle. The specificity of the assay was 99%, as was established with negative sera from regularly vaccinated and from naïve cattle. The sensitivity tested with sera from naturally infected animals was approximately 64% and it was lower than that obtained by serum neutralization (SN) test. Under experimental infection, the Chinese yellow cattle developed lower anti-3AB antibodies than that developed in other species. Duration of anti-3AB antibodies was traced in two herds of naturally infected animals, indicating that anti-3AB antibodies persisted for approximately 6 months after outbreaks. On the basis of this study, we propose that the Chinese yellow cattle may have natural resistance, which limits viral replication and reduces the development of anti-3AB antibodies.

Animals↗

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.

Animals↗