Z.F. Fu

Respiratory disease in foals and the epizootiology of equine herpesvirus type 2 infection

The epizootiology of equine herpesvirus type 2 (EHV-2) infection was investigated in Thoroughbred foals on a stud farm which in previous years had suffered economic loss due to respiratory disease. Sixteen pairs of foals and their dams were selected for this study and all of the foals became infected with EHV-2 by two to four months of age. These animals responded serologically to the virus infection as detected by an enzyme-linked immunosorbent assay (ELISA). EHV-2 infection persisted in these foals for two to six months with constant or intermittent virus recovery. This persistent infection stimulated continuous production of antibodies against EHV-2. As soon as the antibody levels reached their peak at five to six months, the isolation rate of EHV-2 from the nasal cavity of these animals decreased, and eventually by nine months of age virus could no longer be recovered. Respiratory disease was observed in ten of the 16 foals; and two severely affected animals died at two months of age. EHV-2 was isolated from both foals at ante and/or post mortem examination. It is postulated that EHV-2, either as an initiating agent or by means of immnunosuppression, caused the respiratory disease observed in these foals.

A longitudinal study of natural infection of piglets with Streptococcus suis types 1 and 2

Streptococcus suis types 1 and 2 were detected in nasal swabs taken from five litters of piglets sampled twice weekly from birth. The two types had been detected in all pigs by the time they were 38 and 25 days old respectively with mean ages of first detectable infection being 13.5 and 8.5 days. The prevalence of infection was not affected by housing conditions or the population density of pigs. Piglets originating from a sow with vaginal swabs positive for S. suis type 2 were infected earlier than piglets from non-vaginal carriers. It is concluded that infection of piglets with S. suis type 2 may occur during the birth process.

Investigation of the source of haemolytic Escherichia coli infecting weaned pigs.

Attempts were made to discover the source of strains of haemolytic Escherichia coli infecting weaned pigs on a piggery. The organisms were not detected in the faeces of sows in the farrowing house, or in the in the faeces or intestinal tracts of slaughtered bacon pigs or sows. Sows held in a quarantine unit, and their offspring born in the unit, did not excrete haemolytic E. coli until after they were returned to the piggery. The environment of the piggery was the most likely source of infection for weaned pigs, and routine cleaning and disinfection of the accommodation did not prevent infection. Unweaned pigs were however able to transfer haemolytic E. coli to a newly built, previously unused weaning house, and establish a cycle of infection.

Equine herpesvirus type 1 (EHV-1) infection and vaccination with an inactivated EHV-1 vaccine.

Abstract Extract Madam:- We have been investigating episodes of severe respiratory disease in foals during their first year of life in the Waikato district of New Zealand. Most foals are affected at six to ten weeks of age and again at weaning time (4) and the problem has been especially severe on one stud, ten foals having died of respiratory disease there in the past four years. Preliminary investigations on this stud have indicated that equine herpesviruse type 1 (EHV-1) and type 2 (EHV-2) were frequently isolated and might be the initiators of the respiratory disease observed. (5) As part of an attempt to control this problem, an inactivated vaccine * derived from EHV-1 abortifacient strain (1) had been used since 1981. However, neither the epidemiology of these herpesviruses nor the efficacy of the vaccine has been thoroughly examined. In order to more clearly define the problem, an investigation was carried out to establish the patterns of EHV-1 and EHV-2 infections and to determine the effectivenes...

Managemental influences on the selective proliferation of two strains of haemolytic Escherichia coli in weaned pigs

In an experimental study on a piggery it was found that haemolytic Escherichia coli of O-serotypes 138 or 139 proliferated in the intestinal tracts of pigs following weaning, with E. coli of the O-138 type also being occasionally recovered from unweaned pigs, and once from a sow. Organisms of the O-138 type produced heat labile enterotoxin and their presence in weaned pigs was associated with the development of severe post-weaning diarrhoea. E. coli of O-139 type produced a vero cell cytotoxin and were associated with a milder diarrhoea in weaned pigs. Under various managemental circumstances the O-138 type E. coli almost invariably proliferated after weaning. The O-139 strain of E. coli did however proliferate rather than the O-138 strain following the movement of weaned pigs to new accommodation, after weaned pigs were returned to their sow and then weaning again 5 days later, and very occasionally in pigs weaned at 5 weeks of age. In all these cases earlier proliferation of the O-138 E. coli had been detected, suggesting that this may be a prerequisite for proliferation of the O-139 strain.

Epidemiology of typical and atypical rotavirus infections in New Zealand pigs.

Polyacrylamide gel electrophoresis (PAGE) and enzyme-linked immunosorbent assay (ELISA) were employed to investigate the epidemiology of typical and atypical rotavirus infections in five piggeries. Of 152 faecal samples examined, 46 (30 per cent) were positive by ELISA for group A rotavirus. Rotaviruses with electrophoretic patterns resembling groups A, B and C were detected. At least two and up to five different rotavirus electrophoretypes (typical and/or atypical) were detected in each of the five piggeries. Out of 152 faecal samples examined, 28 (18 per cent) contained rotaviruses with group A electrophoretypes, 9 (6 per cent) with group C but only 1 with Group B. Six samples contained both group A and group C rotaviruses. No common electrophoretypes of group A or C rotaviruses were detected in these five piggeries. The PAGE technique was also used to analyze group A rotavirus isolated sequentially from another piggery over a three year period. A single electrophoretype was found during the first two years, but in the third year a different electrophoretype was detected.

Detection of an atypical (possibly Group C) rotavirus in New Zealand pigs.

Abstract Extract Madam:— I wish to report the first detection of an atypical (possible Group C) rotavirus in New Zealand pigs.

Isolation of a reovirus from a broiler chicken flock with high early mortality

A reovirus was isolated from a flock of 12,000 broiler chickens which experienced a total mortality of 6.3% up to 35 days. The reovirus produced large syncytia in primary chicken kidney cell cultures with eosinophilic intracytoplasmic inclusion body formation. Infected cells reacted with fluorescein conjugated specific anti-reovirus serum. Negatively strained virions had a double shelled appearance with overall diameter of 65 to 70 nm. The nucleic acid had ten discrete segments with electrophoretic mobilities as would be expected for a reovirus.

Rotaviral diarrhoea and its treatment in a foal

A severely dehydrated foal with a history of acute diarrhoea was presented to Massey University for treatment. Rotavirus was demonstrated in the faeces by electron microscopy. The failure to detect other pathogens suggested that rotavirus was the primary aetiological agent. Successful treatment of this case is described and the principles of treatment for diarrhoea, particularly fluid therapy, are reviewed. Antibodies to rotavirus were detected in the sera of nine mares and their foals on the stud that referred the case, indicating that rotaviral infection was probably endemic.

Letters to the Editor: Equine herpesvirus type 1 infection — A reply

Extract Madam:-; Thank you for the opportunity to reply to the comments of Dr Studdert(3)concerning our letter to this Journal.(2)