Leptospirosis is a disease caused by bacteria known as Leptospira. It can affect almost all mammals, and is one of the most common diseases transmitted from animals to humans.
As New Zealand has only two native land mammals (both bats), Leptospira are thought to have come to New Zealand via imported stock animals and other introduced mammals such as rats, hedgehogs and possums. This situation is unique and influences the management strategies and decisions around diagnostics in this country.
While many animals are infected without any symptoms, the disease can have an impact on production. Some strains of Leptospira are adapted to certain mammalian hosts referred to as “reservoir hosts” and these reservoir host animals shed large amounts of infectious bacteria via their urine into the environment. Leptospira can survive for extended periods of time in damp soil and can be spread rapidly in flood conditions.
Humans usually become infected via direct or indirect contact with infected urine. The bacteria invade either through the body’s mucus membranes or through cuts and abrasions. In people it can cause a minor flu-like sickness, but may also make some people seriously ill, needing intensive care at hospital. They may be off work for several months, have lasting kidney or liver damage, and may suffer long term fatigue and depression. Traditionally the disease has mostly been occupationally-acquired with strong links to the meat processing, farming and forestry industries. Overseas, leptospirosis has also been linked with outdoor recreational pursuits. Leptospirosis is a dynamic disease and the preferred reservoir host, the geographical range of the disease and, the relative importance of different strains can change over time.
Two different leptospiral species (L. borgpetersenii and L. interrogans) have been isolated from NZ animals. Leptospira are also commonly classified by their serological characteristics (serovars). In this country these are L. borgpetersenii serovars Hardjobovis, Ballum, Balcanica and Tarassovi and L. interrogans serovars Pomona and Copenhageni. In NZ serovars Hardjobovis, Pomona and Ballum are currently those most commonly identified with disease in humans whilst Hardjobovis and Pomona are the types most significant in livestock. Although much less common, dogs can also become infected and may pose a risk to their owners.
REVIEW of Leptospirosis in People: Levett 2001
REVIEW of Leptospirosis in New Zealand: Marshall and Manktelov 2002