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Biomedical subjects

N H Christensen

Publications and source records attributed to N H Christensen.

At least 19 recordsLinked to original sources
PubMed2006

Serological survey of the infectious disease status of Old English Game fowl in the lower North Island, New Zealand.

AIM: To investigate the serological status of Old English Game (OEG) cockerels for a range of infectious diseases of poultry. METHODS: Standard methods were used to screen serum collected from approximately 200 birds during routine dubbing operations, in 2004 and 2005. RESULTS: There was no serological evidence of infection with Newcastle disease, infectious bursal disease, or Salmonella Pullorum. Antibodies to infectious bronchitis virus, avian encephalomyelitis (AE) virus, Mycoplasma gallisepticum and Mycoplasma synoviae were detected. CONCLUSIONS AND CLINICAL RELEVANCE: The disease status of OEG birds is similar to that of commercial poultry.

Animals↗
PubMed2001

Characterisation of New Zealand isolates of infectious bursal disease virus.

Isolates of infectious bursal disease virus (IBDV) were obtained from domestic poultry in New Zealand in 1997 and 1998. An in-vivo pathogenicity study carried out in specific pathogen free (SPF) chickens demonstrated the low virulence of one of the virus isolates. The nucleotide sequences of the hypervariable region of the VP2 gene of two isolates were determined and compared with published sequences of strains from other countries. The deduced amino acid sequence of the two New Zealand IBDV isolates showed 100% identity with each other, suggesting that little genetic drift had occurred. Phylogenetic analysis showed that the New Zealand isolates were more closely related to two attenuated IBDV strains (Cu1 and PBG98) than to classical (STC and 52/70), very virulent (DV86), variant (variant E) or Australian (002-73) strains. The results support the hypothesis that an attenuated strain of the virus was inadvertently introduced into the NZ poultry population in 1993.

Amino Acid Sequence↗
PubMed1999

Evaluation of serological, histological and immunocytochemical methods for the detection of infectious bursal disease virus infection in broiler flocks in New Zealand.

AIMS: TO study and compare three diagnostic methods for the detection of infectious bursal disease virus (IBDV) infection. METHODS: Samples of sera and bursae were collected from two flocks from each of two broiler farms (Farms A and B) in which IBD had occurred or was suspected to have occurred. Sera were tested in ELISA and agar gel precipitation tests for the presence of IBD antibodies. Bursae were examined histologically for evidence of IBD lesions. An immunocytochemical test was developed to detect IBDV antigens in sections of bursa. RESULTS: Bursae from serologically negative, 45-day-old birds from Farm A, Flock 1 and from serologically positive 49-day-old birds from Farm B, Flock 1 had histological and immunocytochemical evidence of IBDV infection. Birds from Farm A, Flock 2, sampled 12 months after the sampling of Flock 1, and specific-pathogen-free birds, showed no evidence of IBDV infection by any of the three diagnostic methods. Birds from Farm B, Flock 2, sampled on four occasions, were positive for IBD at 20 days of age by histology and immunocytochemistry, but did not seroconvert until 42 days of age. CONCLUSIONS: Serological testing is not a reliable method for the detection of IBDV infection in New Zealand broiler flocks because antibodies may not have developed to detectable levels by the time of slaughter. Histological examination of bursae allowed the demonstration of IBD-like lesions, but these need to be differentiated from those caused by other agents. The immunocytochemistry test was able to detect early IBDV infection. It provided a rapid, definitive diagnosis and may be useful in control programmes. The results from Farm A demonstrate that strict biosecurity measures can be successful in the eradication of IBDV.

Journal Article↗
PubMed1997

Megabacteriosis in a flock of budgerigars.

Megabacteriosis was diagnosed as the cause of depression and wasting in a flock of breeding budgerigars in the Manawatu. Large numbers of megabacteria were detected in direct smears from mucosal scrapings of the proventriculus of two birds and in the faeces of live birds. The diagnosis was confirmed by demonstrating a chronic proventriculitis histologically associated with megabacterial organisms. Treatment of seven individuals with amphotericin B resulted in clinically sustained weight gain over a 10-week period. Treatment of the whole flock resulted in the resumption of normal condition, behaviour and activity.

Journal Article↗
PubMed1995

Evaluation of the effects of enzootic pneumonia in pigs on weight gain and days to slaughter under New Zealand conditions.

The effects of enzootic pneumonia on average daily weight gain and number of days taken to reach slaughter weight was studied in 333 bacon-weight pigs. Each 1% of lung volume affected by enzootic pneumonia was shown to reduce average daily gain by 2.2 grams and increase the numbers of days to slaughter by 0.61 days. The cost of these reductions in performance was calculated to be about NZD 1 for each 1% of lung affected.

Journal Article↗
PubMed1994

EDS 76 HI antibodies in a flock of free-range layers.

An investigation of poor laying performance in a flock of free-range hens revealed high levels of serum antibodies to EDS 76 in the flock initially examined and in another, older flock on the same farm. These flocks had contact with ducks on a farm dam and were supplied with untreated drinking water from the dam. Serological evidence indicated that another flock supplying the same egg packing station had been infected with EDS 76 virus. Little serological evidence of EDS infection was detected from five other flocks supplying the packing station, parent breeders or the ducks resident on the dam. Therefore, the source of the EDS 76 virus remains conjectural.

Journal Article↗
PubMed1993

Faecal excretion of Salmonella hadar from calves grazed on pastures fertilised with S. hadar-contaminated broiler litter.

The risk of Salmonella hadar infection in weaned calves grazed on pasture artificially contaminated with the organism via broiler litter applied at commercial dressing rates was assessed. A group of four calves was grazed on artificially contaminated pasture and a control group was grazed on an adjacent identical paddock. A ninth calf was given S. hadar together with an anthelmintic drench, and a tenth was fed on a mixture of contaminated broiler litter and hay for 36 hours. Rectal swabs were collected from the calves at weekly intervals and examined for the presence of salmonellae. Two of the calves in the group on contaminated pasture and both the control positive calves shed S. hadar in their faeces on at least one occasion. The S. hadar contamination was detectable on the pasture for at least 42 days after application of the contaminated litter.

Journal Article↗
PubMed1990

Monitoring the health of pigs in New Zealand abattoirs.

A survey of the prevalence of pneumonia, ascariasis, mange, oesophagogastric ulcers and porcine intestinal adenomatosis was carried out during 1986-90 on 2792 baconer pigs from 46 herds located in Canterbury, North Otago and the southern part of the North Island of New Zealand. Enzootic pneumonia had an overall prevalence of 45%, ascariasis 13% and clinical mange 13%. Oesophagogastric ulceration was a problem in certain herds only, whilst porcine intestinal adenomatosis and associated ileal lesions had a very low prevalence (7%). Examination of 534 snouts for atrophic rhinitis revealed a prevalence of 31%, but most of the lesions recorded were very mild.

Journal Article↗
PubMed1989

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.

Journal Article↗
PubMed1988

A study of the effects of Marek's disease in a broiler flock.

In a flock of 17000 broilers, characteristic Marek's disease (MD) paralysis, accompanied by increased mortality occurred during the fourth week of the flock's life. Cytolytic lesions and atrophy in the bursae of Fabricius, and the severity of lymphocytic infiltration of nerves, livers, proventriculus and brain are suggestive of the involvement of MD virus of greater pathogenicity than has been encountered previously in New Zealand.

Journal Article↗
PubMed1988

Age-related functional changes in the follicle-associated epithelium of the bursa of Fabricius in Shaver cockerels.

A study of the age-related functions of immunologically important components of the bursa of Fabricius in Shaver cockerels showed that endocytosis of carbon particles by the specialised follicle-associated epithelium was at a high level from hatching until 5 weeks of age and thereafter declined until at 18 weeks it could no longer be detected. The follicle-associated epithelium had marked non-specific esterase activity during the first 15 weeks of life as determined by a standard acid alpha-naphthyl acetate esterase method. The absolute weight of the bursa was at a maximum at 9 to 10 weeks. Involution began before 14 weeks and was complete by 22 weeks. The results indicate that the critical period for the bursa in regard to acquiring immunity from either local vaccination or environmental challenge is likely to be within the first five weeks of life.

Journal Article↗
PubMed1986

P & P practice.

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Letter↗