In New Zealand, leptospirosis is particularly prevalent amongst farmers. This year, cases of the disease have already more than doubled to previous years in Hawke’s Bay. Jackie Benschop, Professor of Veterinary Public Health at Massey University, has been researching the disease for years. Her current studies for the Health Research Foundation – Hawke’s Bay look into testing and identifying different strains. She explains why this is crucial to be able to address this problem that seems to knock even the toughest farmer off his / her feet.

Transmitted via animal urine (as well as affected water or soil), leptospirosis is contracted through the mucosal membrane such as eyes, nose, mouth, or cut/grazed skin. Not surprisingly, it is therefore often detected amongst our farming communities. Vaccination of livestock has generally shown a high protection rate, but farmers must consider it a programme, one to be repeated every year, if they wish to minimise the risk of infection of the herd or flock – and themselves. ‘Vaccinate young stock early, ideally when four-to-six-weeks old, follow up with a booster 4 weeks later and then vaccinate adult stock yearly’, says Jackie.

Symptoms of leptospirosis are not to be taken lightly: ‘Everyone with leptospirosis feels as if they have been hit by a train. They get a very high fever, one that develops rapidly and results in severe chills too. Intense headaches and exhaustion are other shared symptoms. Some patients also have tummy aches, a cough or diarrhoea. You can see how the disease is sometimes confused with Covid or influenza.’ Patients are severely ill for a good week, if not weeks, and about 50% of patients is still not right eight months after first becoming ill. One of Jackie’s studies found that 2/3 of patients went to hospital, where they stayed for an average of 4 nights. About a quarter of those who went to hospital ended up at ICU, she adds. Visiting the hospital early on seems a wise decision, as immediate effects such as severe dehydration, aren’t the only concern: ‘The second phase of the disease we call the “tissue phase”, and this could cause meningitis, or damage to the liver or kidney.’ On the bright side, leptospirosis is very sensitive to simple penicillin. Not requiring a heavy medicine (with possible side effects) is a huge benefit. Nevertheless, avoiding the disease is obviously preferable.

Whereas leptospirosis has been on a steady decline since the 1970-ies thanks to the vaccination programme being rolled out, this year we have seen an unusual spike amongst the Hawke’s Bay farming community: ‘Leptospirosis notifications had already risen a little due to a long, wet summer. But after cyclone Gabrielle, we definitely saw a clear spike of cases in Hawke’s Bay: 35 already this year, which is more than double the numbers of prior years. International trends confirm this association: flooding has shown links to leptospirosis spikes overseas as well’, says Jackie. She explains how the disease spreads via liquids, which makes a flood an ‘ideal’ environment for the disease to spread. But there is another factor that influences this: ‘Floods are also a great breeding ground for rodents, as post-flood destruction means easier access to food which is scattered around.’ Rodents are another species that is known to carry and transmit leptospirosis, yet they do seem to carry other strains than for example cattle does.

Specific strains spreading amongst specific species is a key focus of Jackie’s research. Testing for leptospirosis strains is currently challenging, as this test requires for the patient to return for a second test weeks after the first – and most farmers don’t return for this second test. The alternative test, which is PCR-based, just gives a quick ‘yes / no’ as to the presence of leptospirosis and doesn’t provide any insights into the specific strain. The test Jackie’s lab developed, led by Dr Shahista Nisa, is a molecular typing assay test which can inform us of the strain detected. ‘This test looks at the DNA sequence and comes back with a ‘fingerprint’ that we can match with a specific strain.’ Jackie and Shahista hope this will enable a better identification of different strain types – and therefore the determination of most likely root causes (cattle / rodents). It could also shed light on the question whether those causes have shifted since the cyclone and could open the door to better addressing the issue, and for the development of better prevention models moving forward.

The study is expected to complete mid 2024.