Study REPORT
Serological survey of leptospiral antibodies in clinically unwell dogs in New Zealand Keara Brownlie BVSc, Companion Animal Veterinary Advisor, Zoetis
Aim
To investigate the prevalence of immunoglobulin M (IgM) positive antibody response to leptospirosis in clinically unwell dogs in New Zealand
Introduction
Leptospirosis is a spirochaete bacterial disease which affects all mammals worldwide. It is also considered one of the most common zoonotic diseases to affect humans globally with potentially fatal consequences (Levett 2001). Infected and carrier animals, including dogs, will shed leptospires in their urine. In this way, infection can spread to other species including humans. Dogs are recognised as a significant reservoir for human infection in tropical countries, but, although it has a temperate climate, cases have been attributed to contact with dogs in New Zealand (NZ) (Sanhueza et al. 2012; Thompson 2012). Due to relatively high rates of infection in humans (ESR 2019), considerable effort has been made to reduce the risk of human infection through staff education and livestock vaccination in high-risk agricultural industries such as dairy farming and abattoirs in NZ. Despite this, relatively little attention has been paid to the role of dogs in the infection cycle for leptospirosis in NZ. There are over 250 pathogenic serovars of Leptospira interrogans and borgpeterensii, in addition to nonpathogenic serovars of Leptospira biflexa. L. borgpeterensii serovars
Balcanica, Hardjo, Ballum, Taravossi and L. interrogans serovars Pomona and Copenhageni which are known to be endemic in the livestock, rodent and possum populations of NZ (Hathaway et al. 1981). Of those present in NZ, Copenhageni, Hardjo, Ballum and Pomona have been recognised internationally as causing disease in dogs (Miller et al. 2007). Antibodies to all of these serovars have been identified in dogs in NZ (O'Keefe et al. 2002). A 2013 survey of 655 samples submitted to veterinary laboratories established that serovar Copenhageni was found most commonly (10.3% of included dogs), with serovars Hardjo, Pomona and Ballum identified less commonly (3.5%, 1.1%, 0.8% respectively) (Harland et al. 2013b). The agricultural compounds and veterinary medicines (ACVM) register lists two leptospiral vaccines licensed for dogs in New Zealand, Leptoguard (Zoetis NZ, Auckland NZ) and Nobivac Lepto (MSD Animal Health, Upper Hutt, NZ). Both these vaccines contain inactivated Icterohaemorrhagiae which stimulates active immunity to both Icterohaemorrhagiae and Copenhageni serovars (Schoone 1989). The most recent serological survey of leptospiral antibodies in dogs in New Zealand concluded that there was no significant difference in the prevalence of positive leptospiral titres between dogs in the North and South Islands. However, there was uneven geographical distribution of samples submitted (Harland et al. 2013b). A recent survey on vaccination policies for dogs across New Zealand showed that 90/96 (94% )of responding veterinarians in the upper North Island often or always recommended vaccination of dogs against leptospirosis. In comparison,
52/66 (79%) of responding veterinarians in the South Island rarely or never recommended leptospirosis vaccination (Cave et al. 2016). This is in line with the anecdotal experience of Zoetis representatives speaking to veterinarians across New Zealand. There is a common perception that leptospirosis is diagnosed infrequently in dogs residing south of Lake Taupo and even more rarely in dogs south of Nelson. Anecdotally it is for this reason that veterinarians rarely consider testing unwell dogs for leptospirosis south of Nelson. Additionally, few veterinarians recommend vaccination against leptospirosis for dogs residing south of Taupo. Despite this, Zoetis representatives typically receive one to two reports of confirmed leptospirosis in dogs residing south of Nelson every year. The presenting signs of leptospirosis in dogs include pyrexia, anorexia, lethargy, vomiting, anaemia, uveitis, abortion, pulmonary haemorrhage and signs of renal and/or hepatic failure. Dogs can present with only mild, non-specific clinical signs such as fever, anorexia, depression and abdominal pain. Historically, diagnosis of leptospirosis in dogs has been considered challenging. For these reasons, dogs presenting with nonspecific clinical signs may be unlikely to be tested for leptospirosis and could be misdiagnosed, further perpetuating the perception that leptospirosis does not commonly affect dogs in Southern New Zealand. It is considered likely that leptospirosis is under-diagnosed in both working and pet dogs in NZ (Harland 2013a), particularly in regions where leptospirosis in dogs is considered rare, and where it may not feature on the differential diagnosis list for some
Contact: Keara.brownlie@zoetis.com
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Companion Quarterly: Official Newsletter of the Companion Animal Veterinarians Branch of the NZVA | Volume 32 No 3 | September 2021
