Procedures for preventing transmission of foot-and-mouth disease virus (O/TAW/97) by people

The aim of this study was to determine personal hygiene protocols and animal avoidance periods needed to prevent transmission of FMDV (O/TAW/97). Forty-six, 9-week-old barrows free of FMDV were randomly allocated to five treatment groups and a control group. Investigators contacted and sampled FMDV-inoculated pigs for approximately 40 min and then contacted and sampled sentinel pigs after using no biosecurity procedures, washing hands and donning clean outerwear, or showering and donning clean outerwear. Personnel were sampled for nasal carriage of FMDV for 85.43 h. Contaminated personnel did not transmit FMDV to susceptible pigs after handwashing or showering, and donning clean outerwear. FMDV was transmitted when biosecurity procedures were not used. FMDV was not detected in nasal secretions of investigators. Thus, extended animal avoidance periods do not appear to be necessary to prevent transmission of FMDV (O/TAW/97) by people to pigs when organic material is removed through handwashing/showering and donning clean outerwear. This study supports similar findings in a previous publication using FMDV (O/UK/35/2001).     

Horizontal transmission of Aujeszky's disease virus from sheep to pigs

Eight 2-month-old merino lambs were inoculated intranasally with different (10(2.0)-10(5.0)TCID50) amounts of Aujeszky's disease virus (ADV). Electron microscopic studies indicated that ADV replicated in extra-neural sites, in the epithelial cells of the mucosa of the upper and lower respiratory tract. Although the virus was excreted continuously in nasal discharges, horizontal transmission to contact lambs failed. The surviving exposed and contact lambs had no demonstrable antibodies against ADV and they were susceptible when challenged by ADV. However, the virus was transmitted to susceptible pigs in contact with the exposed lambs. One of the five contact pigs showed characteristic clinical signs of Aujeszky's disease, developed a nonsuppurative meningoencephalomyelitis and ADV was recovered from the brain, nasal discharge and other organs. Restriction enzyme analysis of DNA from this virus confirmed the sheep origin of the isolate. The other 4 pigs seroconverted. ADV infection in sheep is therefore a possible source of infection for pigs, but the lack of horizontal transmission in sheep was confirmed.     

Quantitative risk assessment of foot-and-mouth disease introduction into Spain via importation of live animals

Spain has been a foot-and-mouth disease (FMD)-free country since 1986. However, the FMD epidemics that recently affected several European Union (EU) member countries demonstrated that the continent is still at high risk for FMD virus (FMDV) introduction, and that the potential consequences of those epidemics are socially and financially devastating. This paper presents a quantitative assessment of the risk of FMDV introduction into Spain. Results suggest that provinces in north-eastern Spain are at higher risk for FMDV introduction, that an FMD epidemic in Spain is more likely to occur via the import of pigs than through the import of cattle, sheep, or goats, and that a sixfold increase in the proportion of premises that quarantine pigs prior to their introduction into the operation will reduce the probability of FMDV introduction via import of live pigs into Spain by 50%. Allocation of resources towards surveillance activities in regions and types of operations at high risk for FMDV introduction and into the development of policies to promote quarantine and other biosecurity activities in susceptible operations will decrease the probability of FMD introduction into the country and will strengthen the chances of success of the Spanish FMD prevention program.     

The airborne dispersal of foot-and-mouth disease virus from vaccinated and recovered pigs, cattle and sheep after exposure to infection.

Foot-and-mouth disease virus was detected during two periods in the air of looseboxes which housed susceptible, vaccinated or recovered pigs, cattle or sheep exposed to infection. The first was 30 min to 22 h after exposure and occurred in all animals. The second was two to seven days after exposure and occurred with those susceptible and vaccinated animals which developed clinical lesions, and with vaccinated and recovered pigs and sheep, which did not develop clinical lesions. Vaccination of animals before exposure resulted in less or no virus being detected. The virus during the first period was attributed to virus trapped on the animal during exposure, and the virus during the second period to limited multiplication in the respiratory tract. Control of movement for two weeks after contact with infection is suggested as a means of preventing spread of foot-and-mouth disease in areas that contain vaccinated animals.     

Cell-mediated immune responses of suckling pigs inoculated with attenuated or virulent transmissible gastroenteritis virus

Two litters of suckling pigs seronegative for transmissible gastroenteritis (TGE) virus were orally inoculated with live attenuated (P115) or virulent (M5C) strains of TGE virus. A third seronegative litter (controls) was given cell culture fluids from uninfected cells. Lymphocytes were collected from blood, spleen, mesenteric lymph nodes, and Peyer patches of euthanatized pigs at 0 day and approximately weekly until 26 days after exposure and at approximately 45 days after exposure. Sera were tested for virus-neutralizing antibody titers by use of plaque reduction. Lymphocytes were tested in a lymphocyte proliferation assay for uptake of [3H]thymidine after incubation with the homologous or the heterologous strain of inactivated TGE virus or uninfected cell culture fluids. Only pigs inoculated with virulent TGE virus developed clinical signs of TGE and shed virus. However, all pigs inoculated with TGE virus seroconverted at 6 days after exposure. Responses of lymphocytes from all sources from TGE virus-inoculated pigs peaked between 6 and 14 days after exposure. Pigs inoculated with virulent TGE virus had higher lymphocyte proliferative responses and neutralizing antibody titers than did pigs inoculated with attenuated TGE virus. Cessation of virus shedding coincided with the peak of lymphocyte proliferative responses. The highest responses were with intestinal lymphocytes (mesenteric lymph nodes and Peyer patches) from pigs inoculated with virulent TGE virus. The responses of intestinal lymphocytes from pigs inoculated with attenuated virus were not significantly different from those of pigs inoculated with cell culture fluid. Lymphocytes collected from all sources, except blood from M5C-inoculated pigs, had significantly (P less than 0.05) higher responses to the homologous than to the heterologous TGE virus stimulation.(ABSTRACT TRUNCATED AT 250 WORDS)     

An experimental infection (II) to investigate the importance of indirect classical swine fever virus transmission by excretions and secretions of infected weaner pigs

An experiment was set up to investigate the role of excretions and secretions in the indirect transmission of classical swine fever virus (CSFV). In five small pens, 10 weaner pigs (two pigs per pen) were housed and inoculated with CSFV. Experimental infection was successful in all pigs. The infected pigs were kept in the pens for a period of 15 days after which the pens were depopulated and pigs were killed. At the moment of depopulation, all inoculated pigs were visibly clinically diseased and had high fever. Ten hours later the same pens were repopulated with five pairs of susceptible pigs. From inoculation onwards and especially between depopulation and restocking, the pens were neither cleaned nor disinfected. Four days post-repopulation, three of the susceptible pigs were detected positive on virus isolation. A fourth pig was detected positive 2 days later. Later on, the remaining pigs also became infected, most probably due to contact and between pen infections. It can be concluded that transmission of the virus via excretions and secretions succeeded in four of 10 pigs. This result indicates that transmission of CSFV via excretions and secretions can be of importance in a late, clinical stage of disease.     

A serological survey for antibodies against foot-and-mouth disease virus (FMDV) in domestic pigs during outbreaks in Kenya

Foot-and-mouth disease (FMD) is endemic in Kenya and has been well studied in cattle, but not in pigs, yet the role of pigs is recognised in FMD-free areas. This study investigated the presence of antibodies against FMD virus (FMDV) in pigs sampled during a countrywide random survey for FMD in cattle coinciding with SAT 1 FMDV outbreaks in cattle. A total of 191 serum samples were collected from clinically healthy pigs in 17 districts. Forty-two of the 191 sera were from pigs vaccinated against serotypes O/A/SAT 2 FMDV. Antibodies against FMDV non-structural proteins were found in sera from 30 vaccinated and 71 non-vaccinated pigs, altogether 101/191 sera (53 %), and 91 % of these (92/101) also had antibodies measurable by serotype-specific ELISAs, predominantly directed against SAT 1 with titres of 10–320. However, only five high titres against SAT 1 in vaccinated pigs were confirmed by virus neutralisation test (VNT). Due to high degree of agreement between the two ELISAs, it was concluded that positive pigs had been infected with FMDV. Implications of these results for the role of pigs in the epidemiology of FMD in Kenya are discussed, and in-depth studies are recommended.     

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.     

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.     

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.     

Multiplication of attenuated and virulent porcine parvoviruses in colostrum-deprived, neonatal pigs

Colostrum-deprived, neonatal, 2 days old pigs were inoculated with the attenuated HT-/SK or the virulent 90HS strain of porcine parvovirus (PPV) by the oral or subcutaneous route and sacrificed 2, 4 or 6 days after inoculation. Then, comparison was made on viral multiplication in pigs between the two strains. Pigs inoculated with the HT-/SK strain showed no detectable viremia or HI antibody responses against PPV within 6 days after inoculation. Only in pigs inoculated by the subcutaneous route, a small amount of virus was recovered from the spleen, liver, or mesenteric lymph nodes. These viruses were distinguished from the parental virulent 90HS strain, as examined for rct maker in vitro. When pigs were inoculated with the virulent 90HS strain, viremia appeared in all of them 1 day after inoculation and continued for up to the sacrificed day. Moreover, a considerable amount of virus was also detected from all tissues, including brain, lung, liver, spleen, pancreas, small intestine, and lymph node tissues, in all pigs tested. HI antibodies were first detected 6 days after inoculation.     

Detection of respiratory pathogens in air samples from acutely infected pigs

Pathogens causing significant respiratory disease in growing pigs include Porcine reproductive and respiratory syndrome virus, Porcine circovirus 2, swine influenza virus, porcine respiratory coronavirus, Mycoplasma hyopneumoniae, and Bordetella bronchiseptica. The objective of this research was to characterize the respiratory excretion of these pathogens by acutely infected pigs. Pigs were inoculated under experimental conditions with 1 pathogen. Samples were collected from the upper respiratory tract and exhaled air. All pathogens were detected in swabs of the upper respiratory tract, but only M. hyopneumoniae and B. bronchiseptica were detected in expired air from individually sampled, acutely infected pigs. These findings suggest either that the acutely infected pigs did not aerosolize the viruses or that the quantity of virus excreted was below the detection threshold of current sampling or assay systems, or both, at the individual-pig level.     

Experimental induction of malignant catarrhal fever in pigs with ovine herpesvirus 2 by intranasal nebulization

Malignant catarrhal fever (MCF), a frequently fatal herpesviral disease primarily of ruminant species, has been sporadically reported in pigs. All cases of naturally occurring porcine MCF reported to date have been linked to ovine herpesvirus 2 (OvHV-2), a gammaherpesvirus in the genus Macavirus carried by sheep. Experimental induction of MCF by aerosolization of the virus in nasal secretions collected from infected sheep has been successful in bison, cattle and rabbits. The goals of this study were to determine the susceptibility of pigs to MCF following experimental intranasal inoculation of OvHV-2, and to characterize the disease. Twelve pigs in four groups were nebulized with 10(5), 10(6), 10(7), or 10(8) DNA copies of OvHV-2 from sheep nasal secretions. Three control pigs were nebulized with nasal secretions from uninfected sheep. Three additional pigs were inoculated intravenously with 10(7) DNA copies of OvHV-2 to evaluate this route of infection with cell-free virus. Seven of twelve intranasally challenged pigs became infected with OvHV-2. Five of these seven, all in higher dose groups, developed MCF. Lesions resembled those reported in natural cases of porcine MCF. The most striking and consistent histological lesions were in trachea, lung, kidney and brain. These comprised mucopurulent tracheitis, interstitial pneumonia, necrotizing arteritis-periarteritis, and nonpurulent meningoencephalitis. No infection was established in the intravenously challenged or control groups. The study showed that MCF can be experimentally induced in pigs by aerosol challenge using sheep nasal secretions containing OvHV-2. Domestic pigs are a natural clinically susceptible host for sheep-associated MCF. They represent a useful, cost-effective model for MCF research.     

Evidence of indirect transmission of classical swine fever virus through contacts with people

A strict system for visiting experimentally inoculated and susceptible weaner pigs was used to examine the potential indirect transmission of classical swine fever (CSF) virus by people wearing contaminated boots, gloves and coveralls. The inoculated and susceptible pigs were housed in separate compartments, between which the airborne transmission of the virus was impossible. A worst-case scenario with an intensive visiting protocol and no form of disinfection or hygiene was established. Fifteen days after the pigs were inoculated, infection was detected in one contact pig, and it was concluded that under the conditions of the experiment CSF virus could be transmitted by contact with people.     

Contact transmission of vesicular stomatitis virus New Jersey in pigs

OBJECTIVE: To determine how viral shedding and development or lack of clinical disease relate to contact transmission of vesicular stomatitis virus New Jersey (VSV-NJ) in pigs and determine whether pigs infected by contact could infect other pigs by contact. ANIMALS: 63 pigs. PROCEDURE: Serologically naive pigs were housed in direct contact with pigs that were experimentally inoculated with VSV-NJ via ID inoculation of the apex of the snout, application to a scarified area of the oral mucosa, application to intact oral mucosa, or ID inoculation of the ear. In a second experiment, pigs infected with VSV-NJ by contact were moved and housed with additional naive pigs. Pigs were monitored and sampled daily for clinical disease and virus isolation and were serologically tested before and after infection or contact. RESULTS: Contact transmission developed only when vesicular lesions were evident. Transmission developed rapidly; contact pigs shed virus as early as 1 day after contact. In pens in which contact transmission was detected, 2 of 3 or 3 of 3 contact pigs were infected. CONCLUSIONS AND CLINICAL RELEVANCE: Transmission was lesion-dependent; however, vesicular lesions often were subtle with few or no clinical signs of infection. Contact transmission was efficient, with resulting infections ranging from subclinical (detected only by seroconversion) to clinical (development of vesicular lesions). Long-term maintenance of VSV-NJ via contact transmission alone appears unlikely. Pigs represent an efficient large-animal system for further study of VSV-NJ pathogenesis and transmission.     

Immune responses to foot-and-mouth disease virus in pig farms after the 1997 outbreak in Taiwan

This paper reports on a retrospective study of the antibody responses to structural and non-structural proteins of FMD virus O Taiwan 97 in six pig herds in Taiwan in the year after the 1997 Taiwanese FMD outbreak. All herds were vaccinated against FMD after the outbreak as part of the countrywide control program. Three of the herds had confirmed FMD infections (herds N, O and P) and three herds remained non-infected (herds K, L and M). The serum neutralizing antibody titers and the non-structural protein ELISA (NSP) antibody responses in sows and 1-month-old pigs in the infected herds were higher than in the non-infected herds, but over time a number of positive NSP reactors were detected. From the serological studies and the herd monitoring and investigations it was considered that the FMD NSP positive reactors may not have constituted a true reservoir of FMD virus infection especially in herds where susceptible pigs were no longer present post-exposure or post-vaccination. Pigs vaccinated with an unpurified FMD type O vaccines being used at that time also showed false positive responses for NSP antibodies.     

A study of the ability of a TK-negative and gI/gE-negative pseudorabies virus (PRV) mutant inoculated by different routes to protect pigs against PRV infection

The capacity of a TK-negative (TK-) and gI/gE-negative (gI/gE-) pseudorabies virus (PRV) mutant to protect pigs against Aujeszky's disease carried out by experimental infection with a virulent PRV strain, was tested. There were three groups, each of four susceptible pigs which were inoculated twice by two different schedules. Group 1 received the modified virus by the intradermal (first inoculation)-intramuscular (second inoculation) routes; group 2 was treated by the intranasal (first inoculation)-intramuscular (second inoculation) routes. The third group was left untreated as the control. All of the pigs were challenged intranasally with a virulent PRV strain and they were subsequently injected with dexamethasone. Two pigs in each group were necropsied on days 5 and 15 after dexamethasone inoculation. The challenge exposure resulted in mild clinical signs, increase in growth and a shorter period of virus shedding in vaccinated pigs, whereas the control group showed severe signs of Aujeszky's disease. No difference in the titre of the virulent virus which was excreted by pigs of all three groups, was observed and all animals seroconverted. Both the mutant strain and the wild-type virus established a latent infection although only the latter was reactivated and shed. Slight lesions were observed in target tissues of the vaccinated animals and no significant differences were detected between the two inoculation schedules.     

A novel concept for the control of Aujeszky's disease: experiences in two vaccinated pig herds

A study was conducted to examine the usefulness of a glycoprotein I (gI)-ELISA to monitor Aujeszky's disease virus infection in two vaccinated pig herds; the gI-ELISA can differentiate between pigs infected with Aujeszky's disease virus and pigs vaccinated against Aujeszky's disease with gI-negative vaccines. The two herds had been vaccinated with gI-negative vaccines for several years. The first survey, in September 1986, revealed that approximately 10 per cent of the breeding pigs in a large multiplier herd were seropositive for antibodies to gI of Aujeszky's disease virus, and it was decided to try to eliminate the virus from the herd by gI-ELISA testing and culling of gI-seropositive pigs. A one month quarantine period for incoming stock was established, and only gI-seronegative pigs were admitted to the herd. After two rounds of testing and culling the herd appeared to be free of wild-type Aujeszky's disease virus, and neither Aujeszky's disease virus nor antibodies could be detected either in 21 sentinel pigs placed on the farm or in 347 stillborn piglets or piglets that died shortly after birth. The herd probably remained free of Aujeszky's disease virus until the end of the 27-month period of monitoring except for two of 639 breeding pigs that were unexpectedly found to be positive in the gI-ELISA in November 1987. These sows were culled. A second breeding herd was monitored for antibodies to gI of Aujeszky's disease virus for two years. The gI-seropositive sows constituted approximately 30 per cent of the herd's breeding pigs, but they were not culled.(ABSTRACT TRUNCATED AT 250 WORDS)     

THE INFECTION OF MERINO SHEEP WITH BOVINE EPHEMERAL FEVER VIRUS

Four Merino sheep inoculated intravenously with bovine blood containing ephemeral fever virus showed no clinical signs of ephemeral fever. Two sheep showed a mild haematological response and developed a neutralising antibody which closely paralled that of a steer inoculated at the same time. Leucocytes harvested from these 2 sheep on days 3 and 4 after inoculation with virus reproduced ephemeral fever when inoculated into susceptible steers whilst those harvested on days 1, 2 and 5 did not. Even though this indicates that EFV can multiply in some sheep when they are inoculated intravenously, it cannot be inferred that natural infection occurs.     

Foot-and-mouth disease: a review of intranasal infection of cattle, sheep and pigs

In an outbreak of foot-and-mouth disease (FMD) it is important to identify animals at risk from airborne virus. Investigations have been carried out over the years to determine the dose required to infect cattle, sheep and pigs by the intranasal route. This paper reviews the results of investigations for animals which have been infected by instillation or spraying a virus suspension into the nostrils or by exposure to affected animals through a mask or by indirect contact. The lowest doses were found by use of a mask. With virus from affected pigs given through a mask, doses of 18 infectious units (IU) in cattle and 8 IU in sheep were found to cause infection and give rise to lesions. Overall, cattle required the least amount of virus followed by sheep. Pigs required a dose of 22 IU to cause infection and a dose of 125 IU to give rise to lesions. In many experiments pigs failed to become infected. With all three species the dose varied with the individual animal and the virus strain. For modelling previous outbreaks and in real time, a dose of 8 IU or 10 and 50% infectious doses (ID50) could be used where cattle and sheep were involved. Experience in the field, combined with the results from experiments involving natural infection, indicate that pigs are not readily infected by the intranasal route. However, for modelling purposes a dose of about 25 IU should be used with care. Investigations are needed to determine doses for virus strains currently in circulation around the world. In addition, the nature of the aerosol droplets needs to be analysed to determine how the respective amounts of infective and non-infective virus particles, host components and, in later emissions, the presence of antibody affect the survival in air and ability to infect the respiratory tract. Further work is also required to correlate laboratory and field findings through incorporation of the doses into modelling the virus concentration downwind in order that those responsible for controlling FMD are provided with the best available assessment of airborne spread. Finally, the doses found for infection by the intranasal route could be applied to other methods of spread where virus is inhaled to assess risk.