P. Sutmoller

The epizootiological importance of foot-and-mouth disease carriers

1. Susceptible and immunized cattle were exposed to FMDV in varying amounts, and by different routes, and a high percentage of cattle became carriers after pharyngeal or nasal exposure. 2. The percentage of virus “takes” was not altered appreciably by the immune status of the cattle; however, as could be expected, the susceptible cattle more often became clinically ill. 3. If only minimal amounts of virus were inoculated, carriers were sometimes produced without overt disease. In immune cattle, this direct establishment of asymptomatic carriers appeared to be the rule. 4. In immunized cattle, the number of virus “takes” was somewhat reduced when low doses of virus were inoculated by the pharyngeal or nasal route. 5. If the virus was able to establish itself in the pharynx of immunized cattle, active virus multiplication took place in spite of preinfection serum antibody and the absence of clinical signs. Susceptible and immunized cattle were exposed to FMDV in varying amounts, and by different routes, and a high percentage of cattle became carriers after pharyngeal or nasal exposure. The percentage of virus “takes” was not altered appreciably by the immune status of the cattle; however, as could be expected, the susceptible cattle more often became clinically ill. If only minimal amounts of virus were inoculated, carriers were sometimes produced without overt disease. In immune cattle, this direct establishment of asymptomatic carriers appeared to be the rule. In immunized cattle, the number of virus “takes” was somewhat reduced when low doses of virus were inoculated by the pharyngeal or nasal route. If the virus was able to establish itself in the pharynx of immunized cattle, active virus multiplication took place in spite of preinfection serum antibody and the absence of clinical signs.

Improved techniques for the detection of foot-and-mouth disease virus in carrier cattle

A cup probang was used to collect oesophageal-pharyngeal fluid specimens from cattle carriers of foot-and-mouth disease (FMD) virus (Type A). The specimens were assayed for virus content by inoculation of primary calf kidney cell cultures in prescription bottles and in Povitsky bottles for assay of greater volumes. The efficiency of the techniques was improved by treating the specimens with trichlorotrifluoroethane (TTE) prior to assay. With the TTE-treatment, bacterial and fungal contaminants were virtually eliminated and FMD virus apparently was reactivated from neutralizing antibodies or other inhibitors. Aliquot specimens stored at −20° C for more than 2 months did not have an appreciable loss in titer when the TTE treatment was used. Specimens with 50% glycerin added maintained their original virus titers during prolonged storage at −20° C.

Neutralizing activity in the serum and oesophageal-pharyngeal fluid of cattle after exposure to foot-and-mouth disease virus and subsequent re-exposure

Neutralizing activi ty persists in the serum of cattle for many months after recovery from foot-and-mouth disease (FMD) (4, 6). Neutralizing activity has been observed in the saliva (7), oesophageal-pharyngeal fluid (OPF) (13), and pharyngeal scrapings (2) of recovered cattle. Some workers have concluded tha t the ant ibody in bovine saliva is IgA (8, 9), whereas other workers have concluded that the predominant immunoglobulin in bovine mucus secretions is IgG1 (5). Because OPF contains both saliva and mucus, very likely it contains ant ibody of both classes. Antibody is responsible for the neutralization of FMD virus found in the OPF of many cattle after recovery from the disease (7, 11, 13). Recovery of FMD virus from such cattle is enhanced when OPF samples are treated with fluorocarbon (11), which dissociates the virus ant ibody complex (1, 12). Little has been published about the persistence of neutralizing activity in OPF or its relationship to levels of serum antibody. We will report here on the levels of neutralizing activity in the serum and OPF of a group of 5 cattle for 30 weeks after infection with FMD virus and for 4 weeks after reinoculation with the homologous virus. Five grade Hereford steers approximately 1 ~ years old were housed in isolation units (3) throughout the experiment. Infection was produced by the intranasal instillation of 107 plaque-forming units of FMD virus type 0, subtype 1, strain CANEFA-2. The inoculation was repeated 30 weeks later. Samples of serum and OPF were taken at approximately weekly intervals after each exposure. The neutralizing activi ty of the serum and OPF samples was assayed by means of a plaque reduction test (10) in secondary bovine kidney (BK) cell cultures with results reported as the log (base 10) of the reciprocal of the dilution causing a 73 per cent reduction in plaques. The curves were smoothed by means

Foot-and-mouth disease virus: Plaque reduction neutralization test

Studies of the transmission and pathogenesis of foot-and-mouth disease (FMD) require a method of quantitating the neutralizing activity of a number of body fluids in order to assess an animals response to infection or immunization. These studies usually generate large numbers of a variety of samples from each animal including serum, oesophageal-pharyngeal fluid (8), nasal mucus, and lacrimal fluid. The standard virus-varying serum (PDs0) neutralization test in suckling mice (3) is time consuming and expensive. Tissue culture microtiter techniques (10) are more efficient, but low dilutions required for samples with minimal neutralizing activity often produce adverse effects on the cell systems used. CAPSTICK, SELLERS, and STEWART (2) have proposed the use of a plaque reduction neutralization (PRN) test with FMD virus, but there has been scant reference to its use with this agent. WAO~ER and CowAs (9) have described a PRN technique with suspended cells, but large-scale use requires prodigious number of cells. We report here on the development of a PRN test using secondary cell cultures in disposable plastic culture plates (7). This test provides a rapid, efficient assay method. FMD virus, type 0, subtype 1, strain CANEFA-2 1 (01) was used in the developmental stage. Primary bovine kidney cell cultures were dispersed with 0.25 per cent trypsin--0.1 per cent EDTA, pill 8.0, and resuspended in growth medium consisting of Eagles minimum essential medium with Earles salts, L-glutamine, 21 mM sodium bicarbonate, 6 per cent fetal bovine serum, and antibiotics 2. Secondary cultures were prepared in disposable plastic plates with six 35-ram diameter wells 3. Each well was seeded with approximately 800,000

The epizootiological importance of foot-and-mouth disease carriers. II. The carrier status of cattle exposed to foot-and-mouth disease following vaccination with an oil adjuvant inactivated virus vaccine.

1. Fourteen of 30 vaccinated cattle became carriers of foot-and-mouth disease following exposure to virus Types A, O, and C. Nineteen of 32 unvaccinated cattle similarly exposed became carriers. A purified virus acetylethyleneimine-inactivated, oil adjuvant vaccine was used. 2. No appreciable differences were observed among the 3 virus strains in the number of carriers produced or the virus titers of oesophageal-pharyngeal fluid. The number of carriers was lower than might be expected on the basis of previous studies using a strain isolated from carrier cattle. 3. Previous work was confirmed by the finding that the immune status of the cattle exposed to the three strains did not prevent the establishment of the carrier state. Neither was there a demonstrable relationship between the presence of epithelial lesions and the development of the carrier state. 4. Mean virus titers of oesophageal-pharyngeal fluid from vaccinated and unvaccinated carriers were of the same order. Fourteen of 30 vaccinated cattle became carriers of foot-and-mouth disease following exposure to virus Types A, O, and C. Nineteen of 32 unvaccinated cattle similarly exposed became carriers. A purified virus acetylethyleneimine-inactivated, oil adjuvant vaccine was used. No appreciable differences were observed among the 3 virus strains in the number of carriers produced or the virus titers of oesophageal-pharyngeal fluid. The number of carriers was lower than might be expected on the basis of previous studies using a strain isolated from carrier cattle. Previous work was confirmed by the finding that the immune status of the cattle exposed to the three strains did not prevent the establishment of the carrier state. Neither was there a demonstrable relationship between the presence of epithelial lesions and the development of the carrier state. Mean virus titers of oesophageal-pharyngeal fluid from vaccinated and unvaccinated carriers were of the same order.

Detection and properties of a genomic masked viral particle consisting of foot-and-mouth disease virus nucleic acid in bovine enterovirus protein capsid

Abstract Foot-and-mouth disease virus (FMDV) and bovine enterovirus (BEV) were used for simultaneous dual infection of calf kidney tissue cultures. In the harvest fluid a viral agent was found that had the FMDV genome, but (1) was neutralized by BEV-antiserum and not by FMDV-antiserum; (2) had the acid-stability of BEV and not FMDV; (3) had the buoyant density of BEV (1.35 class) and not FMDV (1.45 class); and (4) had the s-rate class (140–150 S) of both parental viruses. Such a particle meets criteria for simple genomic masking. Its ultracentrifugal properties show that the protein coat influenced the buoyant density in CsCl more than nucleic acid, presumably because of permeability to salt.

Foot-and-mouth disease virus: Biological characteristics of virus from bovine carriers

Isolates of FMDV from bovine carriers were compared with the original infecting viruses for changes in biological properties. Occasional marked differences existed between the original virus and succeeding isolates from the same animal. In 2 cattle which were carriers of type A virus and reinfected with type O virus, it was found that some isolates had the antigenic characteristics of both virus types.

Experimental foot-and-mouth disease in sheep and goats: An epizootiological model

Observations were made on the appearance and spread of foot-and-mouth disease (FMD) in groups of sheep and goats after either intranasal inoculation of virus or contact with an infected steer. Viremia was used as the primary indicator of the spread of infection. Of 91 goats exposed to virus, 88 (97%) became infected and 92% of the infected ones had demonstrable viremia. Comparable figures for sheep were 33 of 43 (77%) infected and 72% of these with viremia. It was concluded that goats, being less expensive than cattle to purchase and house, could be suitable experimental subjects for studies of the epizootiology of FMD under laboratory conditions.

The epizootiological importance of foot-and-mouth disease carriers. 3. Exposure of pigs to bovine carriers.

Foot-and-mouth disease virus transmission could not be demonstrated from carrier cattle to susceptible contact pigs, even though the feet of some contact pigs were traumatized to produce skin abrasions and others were given massive doses of embryonated ascaris eggs. Stress by steroid injections did not enhance the virus activity in the pharynx of carrier cattle.