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AbstractAIM: To describe temporal and spatial patterns of the prevalence of pneumonia in lambs in three regions of New Zealand, and determine effects on liveweight gain.METHODS: A longitudinal study was conducted in 1999–2000 on 14 commercial sheep farms, five from the Southland region of the South Island, and five from the King Country and four from the Northland regions of the North Island. Pneumonia was known to be a problem in lambs on all farms selected. On each farm, 400 lambs were randomly selected at weaning and allocated at random to one of two groups (Groups I and II). Lambs in both groups were weighed at 4-weekly intervals. The extent of pneumonic lesions in lungs was scored visually at slaughter in 40 randomly selected lambs after each weighing (Group I). Lambs in Group II were selected for slaughter by the farm manager on a commercial basis of liveweight and body condition, then assessed for pneumonic lesions.RESULTS: Prevalence of extensive pneumonic lesions (≥10% lung surface area affected) increased from December to March from 1.4 to 10.1% lambs in Southland (n=1,917),1.2 to 25.7% in the King Country (n=1,831), and 4.7 to 21.4% in Northland (n=1,485). Overall, 42.3% of lambs in both groups had pneu- monic lesions (n=5,233) and in 15.1% of these, ≥5% of the lung surface area was affected. Daily weight gain in the month prior to slaughter was reduced in lambs for which ≥20% lung surface area was affected in Group I (p<0.05) but not in Group II.CONCLUSIONS: The association between pneumonic lesions and reduced weight gain was highly significant in lambs from Group I, but not from Group II. Thus, pneumonia had a negative impact on weight gain, and selection by farmers of lambs for slaughter counteracted this association in lambs from Group II.CLINICAL RELEVANCE: Pneumonia occurs commonly as a subdinical disease in lambs in New Zealand. It has no public health significance and is not recorded at slaughter plants nor reported to farmer clients. Effects of the disease on daily weight gain of lambs is considerable and costly for lamb producers.

AIM: To examine the spatial and temporal pattern of Mycobacterium bovis (bovine tuberculosis) infection in a population of brushtail possums (Trichosurus vulpecula) after localised possum eradication.METHODS: Possums on a 36 ha site were eradicated and re-population from the surrounding area studied using population surveys conducted approximately every 2 months for 40 months from the cessation of eradication activity (month zero), using a capture-release programme. At each trapping session, all possums were examined for clinical signs of tuberculosis. The diagnosis of tuberculosis was confirmed by the isolation of Mycobacterium bovis, and restriction endonuclease analysis (REA) was used to type the isolates. Infected possums were categorised as residents (present on the site for at least 6 months before diagnosis), range expanders (adult possums which had extended their nearby home ranges to become trappable within the study site), or juvenile immigrants (sub-adult possums which had dispersed into the site from an unknown distance away). This classification was used to identify the location where possums became infected. Capture locations and denning site locations were used to examine the spatial pattern of disease occurrence.RESULTS: Thirty cases of tuberculosis were diagnosed among the 370 possums identified on the study site. Four different REA types (Types 2, 3, 8 and 10) were identified. The first two cases of tuberculosis were diagnosed in Month 4, in mature male possums categorised as range expanders, the third case was diagnosed in Month 6 and the fourth case at Month 9. Each of the first four cases was infected with a different REA type. The subsequent temporal pattern of infection was consistent with transmission from range expander cases and dispersing juvenile immigrants to resident possums. Clinical incidence remained low but persistent until the third year, when the incidence of Types 2, 8 and 10 escalated. Type 3 infections showed an earlier incidence peak, but disappeared from the site when the last known case died at Month 20. Of the dispersing juvenile possums entering the site, four became clinically tuberculous and represented a source of re-infection of other possums.CONCLUSIONS: Re-emergence of tuberculosis after localised possum eradication was due to the continuing reintroduction of infection in mature and immature diseased possums, and not the survival of M. bovis in the environment.

AIMS: To examine natural transmission of bovine tuberculosis (Mycobacterium bovis infection) in captive brushtail possums (Trichosurus vulpecula) and to determine if this mode of transmission could be employed to challenge possums in vaccination studies.METHODS: Three experiments were conducted. In Experiment 1, 11 pairs of possums were housed together in cages, one of the pair having been experimentally infected with M. bovis. Of the in-contact possums 5/11 had been vaccinated with bacille Calmette-Guerin (BCG). In Experiment 2, three susceptible possums were placed in a colony of 19 possums that had been experimentally infected with M. bovis. In Experiment 3, the four most socially active possums in each of two colonies (24 possums in one colony and 23 in the other) were experimentally infected with M. bovis, and 10 of the remaining possums in each colony were vaccinated with BCG.RESULTS: In Experiment 1, transmission of M. bovis infection occurred in only 1/11 pairs. In Experiment 2, none of the three in-contact possums became infected. In Experiment 3, infection was transmitted to 5/20 in-contact possums in one colony and 12/19 in-contact possums in the other. The possums that became infected by natural transmission were significantly more socially interactive than those that remained free of infection (p<0.05).CONCLUSIONS: When susceptible and infected possums were randomly mixed, the rate of transmission of M. bovis was low, but when highly sociable possums were infected the rate of transmission increased markedly. The risk of transmission was dependent on the close proximity of infected and susceptible possums and the frequency and duration of their social interactions. Natural transmission from experimentally infected to incontact possums in a colony would be a useful way of studying the pathogenesis of tuberculosis in this species, and the social behaviour of the possums studied should be taken into account. The high degree of variation in the rate of natural transmission of M. bovis infection between possums makes this mode of transmission unreliable for assessing vaccine efficacy.

ObjectiveTo analyse data from a study of deer herd health and productivity to identify potential risk factors for the occurrence of dystocia.

ExtractIn the correspondence by BD O'Neil published in the New Zealand Veterinary Journal 56, 48, 2008, entitled, “Re: Analysis of the risk of introduction and spread of porcine reproductive and respiratory syndrome virus through importation of raw pigmeat into New Zealand”, the author listed several concerns; we would like to respond to the three specific points raised.