Waging war on emerging diseases

Waging war on emerging diseases

Landcare Research scientists warn that New Zealand is poised on the brink of an “epidemic of epidemics” with, for example, one disease already present having the potential to wipe out our native birds and another to kill iconic kauri. Disease emergence is tipped to worsen due to climate and land-use change, and global travel. Researchers assessing the risks posed by various plant and animal diseases warn that we need to shift focus to pre-empting disease emergence, rather than just responding to it.

Landcare Research epidemiologist Dr Dan Tompkins coordinates a team focusing on three diseases: avian malaria (responsible for numerous bird extinctions overseas), Johne’s disease (a wasting disease of farmed deer, linked to Crohn’s disease in humans) and Phytophthora fungal diseases (linked with death of diverse tree species worldwide).

A survey of avian malaria, the first for over 50 years, has shown the disease to be much more prevalent and widespread than thought. This is bad news for our native birds, which have little resistance to new diseases.

Dan and his team used a new molecular test to find out if the parasites were present in sparrows and blackbirds. They found over 25% of some 400 birds tested positive, with a pattern of decreasing positive results from North Island to South, closely matching the widening distribution of the carrier mosquito.

“It is clear avian malaria is becoming firmly established,” Dan says. “We found it in up to half the non-native birds in Northland, Gisborne, and Hamilton. It could easily spill over into native bird populations. Avian malaria recently caused more than 60% mortality in captive native birds in Auckland and Christchurch, so we know the results of an outbreak could be devastating.”

The team is now studying female mosquitoes bloated from feeding on blood, “to find out whether the parasite is present and which birds and animals the mosquitoes have been biting.” This will tell us whether control of invasive mosquitoes is required to prevent bird declines.”

Johne’s disease Johne’s is an incurable disease of ruminant animals, and kills up to 20% of newborn deer on some farms. The bacterium causing Johne’s disease, Mycobacterium avium subsp. paratuberculosis (or MAP for short), is implicated as a cause of Crohn’s disease in humans. The incidence of Crohn’s has been rising, with more than 800 cases in Christchurch alone.

Johne’s is proving difficult to eradicate. Landcare Research staff suspect that wild animals might be spillover hosts so recently carried out a survey for Johne’s disease.

A team including Graham Nugent and Jackie Whitford found that on infected deer farms a surprisingly wide range of wild animals are infected, from scavenging cats and hedgehogs, to ferrets. The next step will be to see if wildlife away from infected farms are infected. Researchers will also check whether infected wild animals are shedding Johne’s bacteria in their faeces onto the ground, which then could be picked up by deer.

This work will help us make informed decisions whether control of wildlife is required to contain the increase of Johne’s disease in livestock.

Phytophthora – a tongue-twisting cause of tree death Phytopthora species are associated with ill-thrift and death of kauri and other trees, and researchers are developing tools to understand and control it.

Scientists from Landcare Research, ENSIS and HortResearch using modern molecular methods based on DNA have identified several previously unrecognised species in New Zealand, including Phytophthora kernoviae. Previously known only from Cornwall (UK) this species was found on diseased cherimoya trees and from soil under kauri in Northland. Biosecurity New Zealand, which funded the project, declared it an ‘unwanted organism’ and is managing a national response to its presence here.

Phytophthora heveae was found in the 1970s on Great Barrier Island but the recent DNA work indicates this species is distinct and it has been given the “tag” name Phytophthora taxon Agathis (PTA for short). Landcare Research plant pathologist Dr Ross Beever reports that so far PTA is only known on kauri showing trunk lesions and excessive gum bleeding and suspects it may have been accidentally introduced.

Ross’s team will focus on defining the present distribution of Phytophthora. They will look at PTA in particular, investigating whether increased climatic variability might exacerbate the disease. Such information will help us decide whether phytoplasma plant diseases can feasibly be contained and catastrophic root rot outbreaks prevented.

Border control vs. pre-emption Both Ross and Dan stress the importance of pre-emption in dealing with the threat of diseases. Dan says. “No matter how effective border control is, something will always get in and we need to know what systems and management should be in place for dealing with these risks from disease-causing viruses, bacteria, fungi and parasites.

“We need to be aware that consequences of new diseases could be dramatic, Pre-empting threats is much less expensive than dealing with what’s already established.”

ENDS

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