The SARS story and the threat of Asian bird ‘flu

Australia is under increasing threat of a virulent strain of influenza taking hold in our region – a concern held by the majority of health professionals in the field of infectious diseases. If a pandemic ‘flu virus evolved it could be unwittingly brought to Australia within hours of an overseas outbreak through airline travellers, as occurred with the Hong Kong ‘flu in 1969. They could return from a trip to Asia as walking incubators of a disease pandemic. The SARS story Professor Aileen Plant, renowned world leading epidemiologist, led a team to the site of the world's first official SARS (severe acute respiratory syndrome) outbreak in Vietnam; she was also instrumental in efforts to reduce the risk of SARS in Australia. A Vietnamese man who had visited China was hospitalised in Hanoi in February 2003 with a mysterious respiratory illness. At the same time SARS was breaking out around the world in Hong Kong, Singapore, Canada and the Philipines. [Weeks later it was revealed that the pneumonia-like disease had in fact broken out in November 2002 in China.] At least 13 people who checked into the Hotel Metropole in Hong Kong caught SARS from a doctor arriving from southern China who had slept in a room on the same floor; they then inadvertently spread it around the world.

Plant praised the Vietnamese Government for its rigour and honesty in tacking the SARS crisis, which was over within a few weeks in that country. SARS infected about 8000 people in 29 countries and killed close to 800.

The threat of bird ‘flu

In 2004, avian influenza simultaneously broke out in eight different South-East Asian countries - an unprecedented event. To date over 100 million birds (mainly chickens and ducks) have died or have been slaughtered in an effort to halt the spread of the virus. Avian influenza, or bird ‘flu, has the potential to become the next pandemic - as devastating as the Spanish ‘flu or the more recent Hong Kong influenza outbreak in 1969. Bird ‘flu was first seen in 1997 in Hong Kong, where 6 out of 18 people died; in the latest cases 27 people have died in Vietnam and 16 in Thailand.

Three things are needed to start a pandemic: a new virus must be transmitted to humans, the virus must replicate in humans and cause illness, and the virus must spread efficiently from human to human. So far the bird ‘flu has meet the first two of these preconditions.

A pandemic of bird ‘flu would be much, much worse than SARS. Alan Hampson, deputy director of the WHO Collaborating Centre on Influenza Research, says estimates based on the influence of past pandemics on Australia suggest 4 million Australians could catch bird ‘flu, with 100,000 hospitalised and a possible death toll of 10,000 to 20,000. According to Professor Plant, rapid human transmission of bird ‘flu is a real possibility, for example it could happen when a human (or pig, as they can catch human influenza) already suffering from human ‘flu also catches bird ‘flu. Inside the ailing body, the two ‘flu viruses could swap their genetic material and produce a nasty mutant with the fast-spreading capability of human ‘flu. So far there is no indication of such virus swapping – but it is likely to be a case of when not if.

The eradication of bovine pleuropneumonia from Australia by Dr Timothy Mahony

Historically there are three great cattle plagues of the world: foot-and-mouth disease, rinderpest, and contagious bovine pleuropneumonia (CBPP). Incursions of all three have occurred on the Australian continent since European settlement, however only CBPP became established. CBPP entered Australia in late 1858 in Victoria and by 1864 had spread through the eastern Australia states as far north as the Gulf of Carpentaria. The spread of CBPP continued across northern Australia becoming endemic in the large cattle herds in this region. By 1883 it was reported in Northern Territory and also in the east Kimberley region. Once established in these areas eradication in the other states was problematic at best as the markets for the northern herds were in the southern states.

The first experiments aimed at developing a vaccine were conducted as early as 1860. Attempts at legislative control were made through the introduction of Stock Acts between 1888 and 1896 in SA, Victoria, and Qld. In 1892 chief stock inspectors agreed in principle to compulsory vaccination in endemic areas for subsequent movement of stock. However, despite coordination of control efforts between the states, CBPP continued to spread with incursions reported in south-west Western Australia in 1897. Little progress was made over the next forty years on the eradication of CBPP. There were widespread outbreaks in Qld in 1941 and the disease was considered endemic in NSW. In 1948 Qld introduced regulations requiring cattle moving through the state to be vaccinated, however severe epidemics in NSW and Victoria were reported in 1952. Two years later Qld was delineated into endemic areas.

In 1957, almost 100 years after the initial incursion of CBPP, the chief stock inspectors agreed to establish a national eradication campaign. Eradication commenced in Qld and NT in 1961 using vaccination. CBPP lesions were still observed at slaughter in cattle from NT and Qld in 1963 and some clinical disease was reported in NT. Despite vaccination in all northern areas CBPP lesions were found in slaughtered cattle in NT, WA and SA, while an outbreak of disease occurred in Victoria during 1965. Vaccination continued through to 1968 with no confirmed cases of CBPP recorded, however lesions in NT and WA cattle were still observed. Monitoring and vaccination for CBPP continued and in 1973 all properties in Australia were considered free of disease. The Federal Minister for Agriculture announced Australia as being free of CBPP in August 1973.

A number of lessons can be learned from the establishment and eventual eradication of CBPP:

1. The eventual eradication of CBPP was a result of the recognition that CBPP was a national problem and that no progress could be made without cooperation and coordination between all of the states and territories. This is clearly demonstrated by the early history of the disease where efforts at the state level were unsuccessful. On a positive note, the eradication process of CBPP led to the establishment of the first laboratory for the diagnosis of animal diseases in Australia.

2. The importance of integrating basic research through the development of effective vaccines and diagnostic tests into the eradication campaign. Initial attempts at developing a vaccine for CBPP were made in 1860 and efforts for improved vaccines continued over the next 100 years. Similar efforts were made for CBPP diagnosis.

Reference

Newton, I.G. and Norris, R. (eds) (2000) Clearing a continent: The eradication of bovine pleuropneumonia from Australia. CSIRO Publishing: Collingwood, Victoria.

The Australian Wildlife Health Network

Outbreaks of wildlife diseases pose an increasing threat to Australia's trade, biodiversity, human health, agriculture and tourism. These threats can only be prevented by dramatically increasing our understanding of wildlife health. The Australian Wildlife Health Network connects the agencies that defend Australia against these threats.

The aim of the Network is to promote and facilitate collaborative links in the investigation and management of wildlife health (including feral species) in support of human and animal health, biodiversity and trade. The Network coordinates a national wildlife health surveillance system, operates a national database of wildlife health surveillance and diagnostic information, and a registry of wildlife expertise. Core members of the Network include Commonwealth, state and territory departments of agriculture and primary industry, and environmental, wildlife and conservation organisations.

To date, Network members have been involved in investigation of endangered green turtle deaths on the east coast of Australia, wildlife disease incursions in the Northern Territory and South Australia, and in supporting investigation of a new disease affecting Tasmanian devils in Tasmania.

For more information on the Network, email awhn@zoo.nsw.gov.au

Eucalyptus rust (Puccinia psidii) – a serious threat to a national icon by Andrew Geering

Eucalypts (Eucalyptus and Corymbia spp.) are the dominant component of the Australian vegetation, from the tall, wet forests of Tasmania, the snowfields of the Australian Alps, the bonsai forests of the mallee to the savannah of northern Australia. Not surprisingly, eucalypts are critical to the survival of much of the Australian fauna, which utilise them for both food and shelter. Alarmingly, a serious threat to eucalypts lurks offshore, outside the natural range of the trees, in South America. This threat is Puccinia psidii, the cause of rust disease in eucalypts.

Eucalyptus rust is an example of a ‘new encounter' disease. Eucalypts belong to the family Myrtaceae, a large family of plants containing c. 155 genera and over 3000 species. The Myrtaceae, through ancient Gondwanaland links, is predominantly distributed in the southern hemisphere. P. psidii was first reported on red guava (Psidium guajava syn. P. pomiferum) in Brazil, another member of the Myrtaceae that is thought to have originated in Central America. Eucalypts were introduced to Brazil for timber production and an unfortunate consequence was the exposure of the trees to an endemic pathogen able to switch hosts. P. psidii is now considered a serious pathogen in eucalypt plantations in Brazil, with a report of the loss of more than 300 ha of 6-month old seedlings of Eucalyptus grandis in one epidemic.

P. psidii must be regarded as one of the most serious quarantine threats to Australia. P. psidii is unusual amongst rust fungi in having a relatively broad host range, which in addition to eucalypts, includes other Australian plant genera such as the bottlebrushes (Callistemon and Melaleuca spp.) and lilly-pillies (Syzygium and Eugenia spp.). The full host range of P. psidii is unknown, and all genera of the Myrtaceae can be regarded as potentially susceptible. If it were to be introduced in Australia, it is likely that P. psidii would spread rapidly through wind dispersal of spores, and there would be no practical control method in native forests. There is evidence of varying levels of resistance within and between different species of eucalypt, and young trees (less than 2 years old) are more susceptible than old trees. If it were to be introduced to Australia, P. psidii could be very damaging to the native flora, and indirectly, fauna, as well as the hardwood timber industry. The exact impact is unknown, but let's hope we never find out.

Further reading

Coutinho, T.A., Wingfield, M.J., Alfenas, A.C. and Crous, P.W. (1998) Eucalypt rust: a disease with the potential for serious international implications. Plant Disease 82: 819-825.

Floyd, R,, Wylie, R., Old, K., Dudzinski, M. and Kile, G. (1998) Pest risk analysis of Eucalyptus spp. at risk from incursions of plant pests and pathogens through Australia's northern border. CSIRO Entomology, Contracted Report No. 44, p 73.

Park, R.F., Keane, P.J., Wingfield, M.J. and Crous, P.W. (2000) Fungal diseases of eucalypt foliage. In: Keane, P.J., Kile, G.A., Podger, F.D. and Brown, B.N. (eds) Diseases and pathogens of eucalypts. CSIRO Publishing: Collingwood, Victoria, pp. 191-193.

Karnal bunt – a timely reminder by Andrew Geering

In February 2004, two shipments of Australian wheat were rejected by Pakistan because of ‘claimed' contamination of the grain with spores of the fungus Tilletia indica, the cause of the disease Karnal bunt. Thankfully, the spores were shown to be those of a related fungus that infects perennial veldt grass (Ehrharta calycina), a common weed in the wheat belt of Australia. Nevertheless, the incident provides a timely reminder of the trade implications that an incursion of an exotic pathogen into Australia can have.

Tilletia indica is rated as the most serious quarantine threat to the Australian wheat industry. Tilletia indica affects yield and - more importantly - grain quality, by colouring the flour grey and imparting a foul smell, rather like rotting fish. One estimate of the economic cost of this pathogen if it were to become established in Australia is 17 per cent of the value of Australian production ($491 million per year in 1998). An immediate impact of the introduction of Tilletia indica into Australia would be the loss of many markets through quarantine restrictions imposed by importing countries.

When the claims of contamination of the Australian wheat shipments were made in 2004, Australian scientists were able to quickly refute these claims using morphological and molecular techniques, thus averting an escalation of the trade crisis. The incident does, however, emphasise the need for validated diagnostic protocols for exotic plant pathogens, as well as a thorough knowledge of the endemic plant pathogens in Australia.

Further reading

Murray, G.M.and Brennan, J.P. (1998) The risk to Australia from Tilletia indica, the cause of Karnal bunt of wheat. Australasian Plant Pathology 27: 212-225.

Pascoe, I.G., Priest, M.J., Shivas, E.G. and Cunnington, J.H. (in press) Spores of Tilletia ehrhartae, a smut of Ehrharta calycina, are common contaminants of Australian wheat grain, and a potential source of confusion with Tilletia indica, the cause of Karnal bunt of wheat. Plant Pathology.

Wright, D., Murray, G. and Tan, M-K. (2003) A national diagnostic protocol for the identification of Tilletia indica, the cause of Karnal bunt. Plant Health Australia.

Exercise Tethys – preparing for an emergency disease outbreak in the aquaculture industry by Belinda Wright

In 2003, the Australian Government Department of Agriculture, Fisheries and Forestry (DAFF) conducted the world's first national emergency disease outbreak simulation exercise focussed on the aquaculture industry. Exercise Tethys, held in November 2003, simulated a major disease outbreak in the silver perch aquaculture industry. More than 80 staff from eight government jurisdictions and three industry bodies participated in the exercise.

The disease chosen for the simulation was the highly infectious viral haemorrhagic septicaemia (VHS), which is listed by the OIE (World Organisation for Animal Health). The VHS virus has never been reported in Australia, but occurs in the continental part of Europe and has been associated with massive mortalities of herring along the Pacific Coast of the United States and Canada. In Western Europe, annual losses due to VHS have been estimated at US$60 million.

The exercise scenario and activity incorporated a simulated disease outbreak that spread from the initial infected premise to a total of seven farms and two enclosed lakes in three States, as well as an export shipment of live fish. The exercise did not incorporate physical field operations although these activities were simulated as required. The simulated interstate movement of infected fish required a large amount of communication between jurisdictions and a high level of co-operation. All seven participating State and Territory governments were involved in simulations of disease surveillance activities, controls of fish and product movement, and national decision-making and resource allocation. Emergency operations centres were established and participants were required to meet and make decisions. Among other things, participants had to:
++ communicate across five time zones
++ investigate the source of infection
++ deal with and identify resources required for an immediate and protracted response
++ communicate with the media, ministers, departmental executives, industry and the public.