Re: Fifty years of leptospirosis research in New Zealand: a perspective.

The article which appeared in the Jubilee Issue of the New Zealand Veterinary Journal (Marshall and Manktelow 2002) reviewed one of this country's most important zoonotic diseases. I wish to add three important references concerning its first recognition in livestock and humans in New Zealand. The first field cases of leptospirosis in calves due to Leptospira pomona (now L. interrogans serovar pomona) were confirmed in November 1951 on farms in Westland, not in Northland in 1953 as stated in the review. The seminal year for leptospirosis research was 1951 not 1953. Simultaneously, the association with human disease in New Zealand was also recognized and confirmed (Bruere 1952; Kirschner et al 1952). In that year there was a mini-epidemic of cases in Westland involving both calves and humans. It was fortuitous at the time that Kirschner had established methods for the diagnosis of leptospirosis at Otago Medical School. Despite obvious clinical signs, laboratory diagnosis of leptospirosis was not confirmed at Wallaceville (New Zealand's only animal diagnostic station available to veterinarians in 1951) because of logistic impossibilities in both transport and sample preservation. From calf sera collected in Koiterangi (now renamed Kowhitirangi) in Westland in November 1951, Kirschner confirmed my diagnosis of leptospirosis ...

The response of vaccinated rams to experimental challenge using Brucella ovis.

One hundred and thirty eight rams were allocated to four experimental groups. An inactivated Br. ovis vaccine was administered either once by the intraperitoneal route (1 i/p), twice by the intraperitoneal route (2 i/p), or twice by the subcutaneous route (2 s/c), and the last group was left unvaccinated. They were then challenged by the intravenous inoculation of between 123 and 1.23 x 108 live Br. ovis bacteria. The number of rams that succumbed to infection within the four groups was 4135 (11%) for the 2 s/c, 7133 (21%) for the 2 i/p, 9135 (26%) for the 1 i/p and 18135 (51%) for the unvaccinated rams. Vaccination reduced the number of rams that succumbed to experimental challenge and although there were differences between the vaccinated groups, these were not statistically significant. Following challenge, unvaccinated rams were the first to excrete Br. ovis in their semen three weeks following inoculation. Next, those vaccinated by either one or two doses by the intraperitoneal technique began to excrete the organism (five weeks) and then finally those rams vaccinated twice by the subcutaneous route (seven weeks).

Local tissue reaction to the administration of an inactivated Brucella ovis saline-in-oil vaccine by the intraperitoneal route.

An inactivated Brucella ovis saline-in-oil vaccine was administered to 14 adult ewes using both the intraperitoneal route and the subcutaneous route. Pairs of animals were necropsied at intervals between 24 hours and ten weeks after injection. The nature of the local inflammatory reaction to the administration of the vaccine was similar at all sites. The lesion consisted of granulomatous inflammation arranged around droplets of oily vaccine. Diffuse peritonitis was seen at necropsy in 12 of the 14 animals. A local extraperitoneal inflammatory response at the injection site was present in four animals despite careful attempts to deposit the vaccine within the abdominal cavity. A second study of 30 rams vaccinated by the intraperitoneal technique confirmed that extraperitoneal deposition of vaccine commonly occurred and that approximately 20% of animals vaccinated by the intraperitoneal method still had peritonitis six months later.

The serological response of rams to four methods of vaccination against Brucella ovis infection.

A comparative study was made of the serological response of rams to an inactivated Brucella ovis saline in-oil vaccine administered either once or twice by either the subcutaneous or the intraperitoneal route. The serological response of rams to two spaced doses of vaccine was more consistent and more persistent than when a single dose of vaccine was used. The rise in titre was more rapid and the final titre of greater magnitude when the subcutaneous route of administration was used in comparison with the intraperitoneal route. On a serological basis, the most satisfactory vaccination technique investigated consisted of two subcutaneous injections of vaccine administered ten weeks apart. The least satisfactory technique was a single intraperitoneal injection.

Distribution of heterozygous translocations and aneuploid spermatocyte frequency in domestic sheep.

In an analysis of the chromosomes in 1556 metaphase II figures from 26 translocation-carrying rams and 84 figures from 3 normal rams (54, XY), there were no hypermodal cells in the normal rams but 35 such cells in the translocation rams, giving mean aneuploid frequencies of 3.92 percent, 4.29 percent, and 5.29 percent for the rams heterozygous for 1, 2, and 3 translocations, respectively. The translocation chromosome in the heterozygous state was found to segregate evenly during meiosis. Although the effect of heterozygosity was to increase the aneuploid frequency of the ram it is seen that the frequency in all translocation-carrying rams is low and it is thought that these cells are eliminated during spermatogenesis and therefore do not reduce the fertility of the sheep.

Ovine dermatophilosis in young sheep associated with the grazing of Brassica spp. crops.

The occurrence of dermatophilosis in five month old lambs associated with the grazing of Brassica spp. crops is reported on four farms. The prevalence of the disease varied from 3% to 45% within affected flocks. An additional finding was the occurrence of nervous signs in a small number of more severely affected lambs, characterised by a sudden lowering of the hindquarters. The association between dermatophilosis and the grazing of Brassica spp. crops is discussed.

An inherited cataract in New Zealand Romney sheep.

A bilateral cataract was noted to occur in sheep on a New Zealand Romney stud. Extensive breeding trials showed that this defect was inherited as an autosomal dominant. As such this form of cataract is of minimal importance to the sheep industry as control is merely by culling affected individuals.

Aneuploid spermatocyte frequency in domestic sheep heterozygous for three Robertsonian translocations.

In an analysis of the chromosomes in 332 metaphase II figures from 3 triple heterozygous rams (51,xy,t1t2t3) and a further 84 figures from 3 normal rams (54,xy), there were no hypermodal cells in the normal rams but 9 such cells were found in the triple heterozygotes, giving a mean aneuploid frequency of 5.42% which was similar to the levels previously found in the single heterozygotes. Forty hypomodal cells were found in the 6 rams of which a number would have lost chromosomes due to lagging at anaphase I. Individual variation in the aneuploid metaphase II frequency was observed in the triple heterozygotes. A significant surplus of secondary spermatocytes of normal karyotype and a deficit of 25,t1t3 were found in the metaphase II figures from the triple heterozygotes. There was also a significant increase of normal progeny and a deficit of 52,t1t3 and 53,t2 progeny from the matings of triple heterozygous rams and normal ewes. It is possible that the significantly uneven distribution of segregation products in the triple heterozygotes might have been the result of either cell selection or degeneration during spermatogenesis.

Nucleolus organizer region location and 'ring' chromosomes in the bharal.

Silver-staining has been used to identify the nucleolus organizer regions (NORs) in the bharal. These show homology with sheep, goat, cattle and aoudad. The association of the NORs on both telomeres of chromosome 3 results in a 'ring' chromosome.

Inheritance of Ag-stainability of the nucleolus organizer regions in domestic sheep, Ovis aries.

One of the nucleolus organizer regions of sheep is located on chromosome 25, which forms one arm of a Robertsonian translocation chromosome (t3). By mating sheep heterozygous and homozygous for the t3 chromosome, and with various Ag-staining frequencies and deposit sizes, the heritability of the Ag-stainability could be determined. The inheritance of Ag-stainability was studied in 54 sheep in five pedigree groups. It was shown that the Ag-staining of a NOR is a heritable property. Matings of animals heterozygous for Ag-stainability provided an estimate of recombination frequency of the short arm of t3.

Cytogenetics and reproduction of sheep with multiple centric fusions (Robertsonian translocations).

The significance of centric fusions (Robertsonian translocations) in domestic animals, with special reference to sheep, is reviewed. The mating is described of a further 856 ewes with either a normal chromosome number 2n = 54 or carrying one or more of the three different translocations (centric fusions) t1, t2 and t3 in various heterozygous and homozygous arrangements. Rams which were used in the matings were homozygous for one of the translocation chromosomes (2n = 52), double heterozygotes (2n = 52), triple heterozygotes (2n = 51) or were carriers of 4 translocation chromosomes (2n = 50) and 5 translocation chromosomes (2n = 49). A remarkably even distribution of segregation products was recorded in the progeny of all combinations of translocation ewes x translocation rams in those groups in which sufficient animals were available for statistical analysis. Forty-eight chromosomally different groups of animals were mated. Further, the overall fertility of the translocation sheep, measured by conception rate to first service, lambing percentage and number of ewes which did not breed a lamb, was not significantly different from New Zealand national sheep breeding data. In some groups the poorer reproductive performance could be explained by the age structure of the flock and inbreeding depression, which probably affected the performance of some animals. Sheep with progressively decreasing chromosome numbers, due to centric fusion, 2n = 50, 2n = 49 and 2n = 48, are reported. The 2n = 48 category represents a triple homozygous ewe and a triple homozygous ram and is the first report of the viable evolution of such domestic animals. Less than 1% of phenotypically abnormal lambs were recorded in a total of 1995 progeny born over 10 years. It is now considered that there is little or no evidence to suggest that centric fusions in a variety of combinations affect the total productive fitness of domestic sheep. It is suggested that future research should be more actively directed to understanding their genetic significance.

Conservation of nucleolus organizer regions during evolution in sheep, goat, cattle and aoudad.

There are ten nucleolus organizer regions (NORs) in domestic sheep (Ovis aries L.). cattle (Bos taurus L.), goat (Capra hircus L.) and aoudad (Ammotragus lervia Blyth) and these are located terminally on chromosomes with homologous (G-banding patterns. The similarity in number of nucleolus organizer regions in these species may indicate that their ribosomal DNA regions are infrequently involved in exchange events which could lead to different numbers of active nucleolus organizer regions. Other possible explanations of the conservation of number of nucleolus organizer regions in these species are discussed. The homology of NOR location in these species supports the idea that the Bovidae karyotype tends to be fairly stable apart from changes due to centric fusion events.