Epidemiology, diagnosis and vaccination control of leptospirosis in farmed deer in New Zealand : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Veterinary Clinical Science at Massey University, Palmerston North, New Zealand
Leptospirosis is a bacterial zoonotic disease of global importance. It is caused by infection
with pathogenic Leptopsira species. Leptospirosis encompasses a wide spectrum of clinical
or subclinical disease in both humans and animals. In New Zealand (NZ), leptospirosis is
considered to be the most important occupational zoonosis. Livestock farming plays an
important role as a major occupational risk factor for human leptospirosis and farmed deer is
one of the contributing factors.
Commercial farming of deer began in NZ in the early 1970s. It remains the world’s largest
and most advanced deer farming industry. Leptospirosis in farmed deer can cause illness and
possibly sub-clinical production losses. Farmed deer also play an important role in the
transmission of leptospirosis by shedding the organisms in their urine, putting both other
animals and humans at risk. Leptospira serovars Hardjobovis and Pomona are the most
commonly found serovars in this stock group. The first substantial case report of leptospirosis
in farmed deer was in the 1980s but it was not until 2006 that a substantial epidemiological
study of this disease in farmed deer was reported. The purpose of this research was to
improve and extend current knowledge on the epidemiology of leptospirosis on mixedspecies
deer farms, to develop and validate a novel molecular diagnostic tool and to enhance
understanding of control measures and their outcomes by means of vaccination.
A pilot longitudinal seroprevalence survey of leptospirosis on mixed-species deer farms was
conducted. Results from this study revealed that leptospiral infection averaged 70% in all
species on mixed-species farms in the lower North Island of NZ. Co-grazing with infected
sheep and/or cattle was positively associated with deer herd serological status to both
serovars Hardjobovis and Pomona which suggests the possibility of inter-species
transmission. Results from this study justify further investigation of leptospirosis on mixedspecies
farm at the national level.
A collaborative study between Massey University and the WHO/FAO/OIE reference
laboratory for leptospirosis in Brisbane to investigate for exotic serovars in farmed deer
revealed seropositivity to Arborea which has never been found before in NZ. Attempts to
isolate Arborea from kidney samples of farmed deer were unsuccessful and require further
Real-time PCR assay was developed and validated against culture as the gold standard for use
on deer kidney tissue and urine as a research and diagnostic tool for determining infection,
carrier and shedding status of deer. This research revealed that the real-time PCR assay was
highly sensitive (sensitivity: 85% for kidney and 96.7% for urine) and specific (specificity:
99.2% for kidney and 100% for urine). It is a useful tool for the rapid and cost-effective
detection of pathogenic leptospires in clinical samples. It can also be used to quantify the
concentration of leptospires from clinical samples and identify the likely infecting serovar in
NZ when adjunct with a DNA sequencing technique.
Vaccination control for leptospirosis has proven to be efficacious and likely to be costeffective.
Present research has determined the effect of a commercial bivalent leptospiral
vaccine (Leptavoid-2, Intervet/Schering-Plough Animal Health Limited, NZ) on leptospiral
shedding, growth and reproduction of farmed deer under NZ pastoral conditions. The study
was designed to simulate an infection-free herd scenario followed by exposure to natural
challenge. Results have shown the potential of vaccine to improve mean weight gain (up to
6.5 kg) and weaning rate (average 6.9%) in infected herds and prevent urinary shedding after
natural challenge with Hardjobovis. It also provides the first evidence of adverse subclinical
effects on deer production by Hardjobovis alone.
A pilot study to investigate the presence and localisation of pathogenic Leptospira in the
uterus and foetus of female deer revealed evidence of a foetal infection using real-time PCR.
This finding suggests a possible explanation for effects of leptospiral infection on NZ farmed
deer reproduction. However, further study is required to justify this proposition.
This research has contributed significantly to understanding of epidemiology of leptospirosis
in NZ farmed deer, providing objective data to assist producers in decision-making on
leptospirosis control. Furthermore, this study has made available a valuable diagnostic
resource for future leptospirosis studies, and has provided direction for future research into
leptospirosis on farmed deer and mixed-species farms.