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Proceedings of the First Symposium on Marsupials in New Zealand

Introduction

Introduction

Leptospiral organisms are classified by division into serogroups and within serogroups, serovars, on an international basis. There are twelve main serogroups and contained within these groups are more than 130 serovars. In New Zealand, six leptospiral serovars have been isolated, viz.: ballum, pomona, copenhageni, tarassovi, hardjo and balcanica (Table 1). Of these, hardjo and balcanica, which are antigenically very similar, belong to the Hebdomadis serogroup.

Leptospiral infections are very common in domestic stock in New Zealand, with several serovars being represented. Hebdomadis serogroup infections are most relevant to this discussion and have been demonstrated by serology in cattle, sheep and horses. Serovar hardjo has been isolated from cattle (Lake 1973), and it has been assumed that this serovar has been the most prevalent of the Hebdomadis organisms infecting domestic stock.

The per capita prevalence of leptospirosis in humans in New Zealand is amongst the highest in the world (20 cases: 100,000 c.f. U.K. 0.1: 100,000 and U.S.A. 0.02: 100,000) and Hebdomadis serogroup infections are the most common. Serovar hardjo has been isolated from humans by Christmas et al. (1974).

Recently, hardjo was reported as being isolated from the common brushtail possum Trichosurus vulpecula in New Zealand (Brockie 1975; de Lisle et al. 1975).

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Table 1. Leptospires isolated in New Zealand.
SEROGROUP SEROVAR HOST SPECIES FIRST REFERENCE
Pomona L. pomona Bovine 1954
Porcine 1976
Feline 1970
Human 1952
Hebdomadis L. hardjo Bovine 1973
Human 1974
Possum* 1976
L. balcanica Possum 1976
Ballum L. ballum Bovine 1973
Human 1967
Hedgehog 1976
Rat 1976
Mouse 1977
Icterohaemorrhagiae L. copenhageni Bovine 1960
Rat 1951
Tarassovi L. tarassovi Porcine 1976

In 1975 the author made a single isolation of balcanica from a possum in the Pohangina Valley. Serovar balcanica had only previously been isolated from a man in Bulgaria (Janev, cit. Babudieri and Mateev 1961) and from cattle and a pig in Russia (Semenova 1965).

Serovars hardjo and balcanica are within the same antigenic subgroup as determined by factor sera analysis (E. Kmety pers. comm.) and as such the only means of differentiating between these organisms is by isolation of the organism in pure culture and examination by cross-absorption studies on specific antisera of all serovars within the Hebdomadis serogroup. This is a complicated procedure and is performed at W.H.O. reference laboratories. Consequently, the agglutination test used routinely on sera in this country will identify infection due to organisms from a particular serogroup, but will not identify page 159 specific serovars. Similarly, any isolated cultures from animals with leptospirosis can only be identified as to serogroup without definitive typing.

Bearing these facts in mind, a survey was undertaken in the southern half of the North Island to determine the prevalence of Hebdomadis serogroup infections in pastoral possum populations, and to identify the specific serovars involved.