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Biomedical subjects

D K Blackmore

Publications and source records attributed to D K Blackmore.

At least 19 recordsLinked to original sources
PubMed1991

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.

Animals↗
PubMed1990

Experimental studies on the comparative infectivity and pathogenicity of Streptococcus suis type 2. I. Porcine and human isolates in pigs.

Piglets between 1 and 40 days of age were inoculated with varying numbers and with different isolates of Streptococcus suis type 2 by the intranasal, intravenous and subarachnoid routes. Less than 100 organisms of an isolate cultured from apparently normal pigs caused subclinical infection in 1-day-old piglets after intranasal inoculation. This infection was naturally transmitted between litter mates. Intravenous inoculation of a similar isolate in 7-week-old pigs resulted in a sub-clinical bacteraemia in 3 of 8 piglets. One other piglet developed a bacteraemia 7 days after inoculation and concurrently developed signs of lameness and nervous dysfunction. Ten piglets were inoculated by the subarachnoid route with a porcine isolate and two with an isolate from a person with clinical disease. Only the latter two pigs developed the classical signs of nervous disease associated with infection by S. suis type 2. It is concluded that strains of S. suis type 2, of varying pathogenicity for both pigs and man, are endemic in New Zealand. It is suggested that the occurrence of disease is associated with both exposure to a pathogenic strain and other, as yet undetermined, secondary factors.

Animals↗
PubMed1990

Experimental studies on the comparative infectivity and pathogenicity of Streptococcus suis type 2. II. Porcine and human isolates in laboratory animals.

Mice, rats, guinea-pigs and rabbits were inoculated with isolates of Streptococcus suis type 2. An isolate cultured from the tonsils of a healthy pig, produced disease in rabbits after intravenous inoculation but not in mice, rats or guinea-pigs. An isolate of S. suis type 2, that was pathogenic for pigs and had been cultured from a human patient with clinical disease, produced signs of neurological disease in mice, rats and rabbits following intravenous inoculation. There was an apparent dose response in mice with 31% of mice receiving more than 10(6) organisms developing clinical disease, whilst mice receiving less than this did not develop disease. There were no detectable histopathological lesions in the brains or meninges of mice with nervous signs. It is proposed that the disease in mice may mimic that reported in humans and that mice may be a useful indicator species for determining the virulence of isolates cultured from pigs.

Animals↗
PubMed1989

Detection and survival of group A rotavirus in a piggery.

Samples of dust, faeces and effluent were collected from a piggery and examined for group A rotavirus, using a commercial ELISA test, electron microscopy and inoculation of MA-104 cells. Rotavirus antigen was demonstrated in samples collected from farrowing and weaner rooms but not from fattener and sow houses. Rotavirus antigen was also detected in samples collected from a weaner room which had been free of piglets for three months. A cytopathic porcine rotavirus (British isolate SW20/21) was kept at room temperature for four months; it survived with titres reduced by 2 log10. These observations suggest that the environment of commercial piggeries is an important source of rotaviral infection for young piglets.

Animals↗
PubMed1989

Prevalence of Streptococcus suis types 1 and 2 in domestic pigs in Australia and New Zealand.

Using an indirect fluorescent antibody test, 54 per cent of 734 palatine tonsils of conventional pigs slaughtered in Australia and New Zealand were found to be infected with Streptococcus suis type 1 and 73 per cent of 959 were infected with S suis type 2. Variations in the prevalence of infection in pigs from different herds were thought to be due to differences in the sample sizes rather than to real differences in the prevalence between herds. The prevalence of infection with S suis was similar in pigs of either sex and in different age groups. Streptococcus suis type 2 was detected in the blood of 3 per cent of apparently normal pigs slaughtered at a meat processing plant. The presence of this organism in edible tissue may pose a health risk to consumers and meat-workers. Both S suis types 1 and 2 were detected in the vaginas and uteri of slaughtered pigs and the female reproductive tract could be another site for the carriage of infection. Piglets from sows with vaginas infected with S suis type 2 became infected earlier than piglets from sows with uninfected vaginas. No infected male reproductive tracts were detected and venereal transmission of S suis therefore appears unlikely. Three specific pathogen free herds were found to be free from infection with both S suis types 1 and 2. It is concluded that hysterectomy derived piglets are delivered free from infection, whereas some piglets born to sows with uterine and vaginal infections are either born infected or become infected at, or soon after, birth.

Animals↗
PubMed1989

Occupational exposure to Streptococcus suis type 2.

Antibody titres to Streptococcus suis type 2 were measured with an enzyme linked immunosorbent assay (ELISA) in four occupational groups in New Zealand. No veterinary students, 9% of dairy farmers, 10% of meat inspectors and 21% of pig farmers were seropositive to S. suis type 2. The development of antibody to S. suis type 2 was associated with occupational contact with pigs or their meat products. Subclinical infection with S. suis type 2 appears to occur in humans and the antibody produced is of only short duration. The annual incidence of subclinical infection and seroconversion in pig farmers may approach 28%. Thus S. suis type 2 may be one of the most infectious potentially zoonotic agents present in New Zealand, although very rarely resulting in clinical disease.

Animal Husbandry↗
PubMed1986

Differences in blood supply to the cerebral cortex between sheep and calves during slaughter.

Using methylene blue boli, injected via an intracardiac catheter, the blood supply to the brain in two one- to 10-day-old calves and three adult sheep was studied during and after severance of the common carotid arteries and jugular veins. Passage of dye through cerebral vessels could not be observed in the exposed cerebrum of sheep after bilateral severance of major blood vessels. When vessels were severed on one side only, the passage of dye was noted for at least 53 seconds. In calves, after bilateral severance, sequential boli of dye could be detected passing through the cerebral vessels for more than 100 seconds. These results provide an explanation and support for the belief that there are major differences in the onset of insensibility between sheep and calves subsequent to severance of the common carotid arteries and jugular veins. The differences in blood supply to the brain which were demonstrated could be accounted for by differences in the blood supply to the brain by the vertebral artery in sheep and cattle. The effects of slaughter on the blood supply to the eye are discussed as a possible explanation of the disparity between results of studies in this general field which have used retinal responses in their investigations and those which have not.

Animals↗
PubMed1985

Energy requirements for the penetration of heads of domestic stock and the development of a multiple projectile.

The forces and kinetic energy required to penetrate the isolated heads of calves, adult beef cattle, sheep and red deer with a metal probe the same diameter as the bore of an experimental pistol were determined. Approximately 16 and 127 Joules were required to penetrate the heads of adult sheep and cattle, respectively. Using these data a 10 g projectile, consisting of 49 lead pellets and a lead disc in a polyethylene sleeve, was constructed. This projectile, when fired by a charge sufficient to produce a muzzle velocity of 165 m/second, had sufficient kinetic energy to penetrate the heads and brains of cattle, sheep, horses and deer. The projectile was fired from a new design of humane killer with a spring loaded barrel and fitted with a silencer. After penetration of the frontal bones the projectile fragmented and the kinetic energy of its individual particles were insufficient for them to penetrate the opposite side of the head of any of the animals, including one-week-old calves. Fragmentation also caused more brain damage and inhibition of spinal reflexes than a solid free bullet or captive bolt. It is suggested that the use of such a projectile for the emergency slaughter of animals is less hazardous than a solid free bullet and is easier to use and more effective than either a solid free bullet or captive bolt. The projectile was not suitable for killing adult pigs because of problems associated with the frontal sinus.

Animals↗
PubMed1979

Leptospirosis in meat inspectors: preliminary results of a serological survey.

A serological survey of leptospirosis among more than 1000 meat inspectors, from meat works throughout New Zealand, revealed a serological prevalence at a minimum serum dilution of 1:24, of 10.2 percent. Eighty-five percent of serological reactions were to serovars pomona and tarassovi. A highly significant correlation was demonstrated between the serological prevalence of these serovars and the inspection of pigs. Evidence is provided to substantiate the use of titres as low as 1:24 as an indication of previous leptospiral infection. Forty-two inspectors reported medical evidence of previous clinical infection with leptospirosis. Analysis of those who still exhibited a serological response and their individual case histories, indicated that detectable titres of leptospirosis can exist for up to 10 years.

Animals↗
PubMed1979

Non-penetrative percussion stunning of sheep and calves.

Attempts were made to stun lambs, adult sheep and calves by a non-penetrative percussive method. Using an adapted Cash pistol, with a concave padded impact head, impulses were produced which effectively stunned 96% of lambs but induced brain haemorrhages in up to 7% of the animals. The signs and duration of an effective percussive stun were observed and recorded. Calves were readily stunned by percussive methods but brain haemorrhages frequently occurred. Impulses sufficiently large to stun adult sheep, with a non-penetrating impact head, were produced from an adapted Hantover pneumatic cattle stunner. Comparative trials, using electrical and percussive stunners, demonstrated a significant decrease in the prevalence of blood splash in lambs stunned by percussion.

Abattoirs↗
PubMed1978

The serologic and cultural prevalence of Leptospira interrogans serovar balcanica in possums (Trichosurus vulpecula) in New Zealand.

In a serologic and cultural survey of 127 brush-tailed possums (Trichosurus vulpecula) occupying pasture land in New Zealand, leptospires of the Hebdomadis serogroup were obtained from 48 (38%) of the animals sampled. Eight isolates were identified by cross-absorption agglutin ation studies as being Leptospira interrogans serovar balcanica. There was a marked age difference in prevalence with 41 positive cultures from 64 mature adults (64%) and no recoveries being made from juveniles. Isolation of leptospires was aided by the use of a new technique involving the homogenation of whole kidneys in gamma sterilized plastic bags in a "Coleworth Stomacher". The use of this apparatus allowed the processing of whole kidneys and the technique was efficient in both the recovery of leptospires and the prevention of contamination. In view of the fact that serovar balcanica has been recorded previously only in East Europe in man, cattle and pigs, the high prevalence of infection in a wild animal population in New Zealand is an interesting development in the world distribution of this serovar.

Animals↗
PubMed1977

The practical training of New Zealand veterinary undergraduates in meat hygiene.

Development of the veterinary undergraduate course in meat hygiene over a ten year period is discussed. Arrangements and supervision of students during a two week practical course at six specified centres of meat production, and the value of such training in an actual industrial environment are discussed. The timing of this course in relation to the veterinary curriculum and the seasonal nature of the meat industry in New Zealand creates some problems. Training centres must slaughter a variety of animals and have sufficient staff to effectively teach students. Adequate preparation of students and close co-operation with both the Ministry of Agriculture and the meat industry is essential for success.

Abattoirs↗
PubMed1977

Animals and us.

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Animals↗
PubMed1976

Effects of different slaughter methods on bleeding sheep.

One hundred and sixteen sheep were slaughtered by five different methods in an attempt to determine the most practical technique which would result in rapid exsanguination without incision of the oesophagus. Techniques which involve stunning prior to slaughter were compared with the traditional New Zealand method by which fully conscious sheep are slaughtered by almost simultaneous severance of the major blood vessels of the neck and the spinal cord at the occipito-atlantal junction. Total amounts of blood lost and rates of bleeding were compared.

Abattoirs↗