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Japanese encephalitis virus (JEV) first emerged in the Torres Strait of north-eastern Australia in 1995, with three human cases, and widespread infection of pigs on a number of islands. The virus was shown to belong to genotype II. Further cases occurred in 1998, including the first case on mainland Australia on Cape York. A second genotype of JEV, genotype Ia, was reported in mosquitoes and pigs in 2000–04, possibly displacing genotype II. JEV re-emerged in Australia with a fatal human case on the Tiwi Islands, Northern Territory, in 2021, and shown to belong to genotype IV. This case was followed about a year later by a large outbreak of JE; first detected in piggeries in four states, Queensland, New South Wales, Victoria, and South Australia, resulting in reproductive losses affecting 80 piggeries and 42 human cases, with seven fatal cases. The wide geographic spread of cases suggested that the virus had been circulating for a number of months or even years prior to detection, and has led to significant concern that the virus will become endemic to Australia, in a similar ecology to Murray Valley encephalitis virus. Known competent mosquito vectors and ardeid birds, as maintenance hosts, occur in Australia, and it is probable that feral pigs will provide an additional wildlife reservoir of virus. Little is known of the properties of genotype IV, but it is expected to have a similar ecology and pathogenesis to other JEV genotypes.

The selection of papers included in this issue of Microbiology Australia present a broad brush of zoonotic diseases, from those known or described in ancient times such as rabies, first described in the Eshnunna cuneiform law tablets from ancient Mesopotamia dating back to the 18th–19th centuries BC, and glanders, thought to be first described in donkeys by Aristotle in Ancient Greece in 420–450 BC and subsequently by the Romans, to some discovered or recognised as zoonotic within the past 30 years, such as the recently described zoonotic bat-borne pathogens in Australia, and Clostridium difficile, only recently recognised as a zoonotic pathogen. The selection of papers also demonstrates the wide range of zoonotic origins, including arthropod-borne viruses and potentially seafood-borne parasites.

The selection of papers included in this issue of Microbiology Australia present a broad brush of zoonotic diseases, from those known or described in ancient times such as rabies, first described in the Eshnunna cuneiform law tablets from ancient Mesopotamia dating back to the 18th–19th centuries BC, and glanders, thought to be first described in donkeys by Aristotle in Ancient Greece in 420–450 BC and subsequently by the Romans, to some discovered or recognised as zoonotic within the past 30 years, such as the recently described zoonotic bat-borne pathogens in Australia, and Clostridium difficile, only recently recognised as a zoonotic pathogen. The selection of papers also demonstrates the wide range of zoonotic origins, including arthropod-borne viruses and potentially seafood-borne parasites.

The recent pandemic spread of mosquito-borne arboviruses across multiple continents, as exemplified by West Nile (WNV)1,, chikungunya (CHIKV)2, and Zika (ZIKV)3, viruses, together with the continuing disease burden of epidemic dengue viruses (DENVs)1, multiple importations of yellow fever virus (YFV) into populous areas of Asia4, and the potential threat of some other, possibly unknown, emerging arboviral threat, constitute a wake-up call for governments to strengthen surveillance programmes and enhance research into mosquito-transmitted diseases5–7. Rift Valley fever8 (RVFV) and Japanese encephalitis1,9 (JEV) viruses are also important examples of threats to human and/or livestock health. Australia is vulnerable to these arboviral diseases, with risk of importation and outbreak potential varying between viruses10. The risk of exotic arboviral diseases establishing transmission cycles in Australia is dependent on the availability of competent vectors and suitable vertebrate hosts. Therefore, knowledge of the vector competence of Australian mosquito species for exotic arboviruses, potential for the introduction and establishment of exotic vector species, and suitability of vertebrate hosts, are essential components of understanding and mitigating these arboviral threats.

Ross River virus (RRV) is the most common cause of mosquito-borne illness in Western Australians. The virus is maintained in nature principally via transmission between competent mosquito vectors and native (marsupial) vertebrate hosts, although humans are suspected of being amplifiers of RRV in some situations. The influence of prevailing environmental conditions on the ecology of RRV has been extensively documented. Indeed, monitoring of environmental variables, together with vector mosquito populations and infection rates with RRV, now provides effective early warning of elevated levels of RRV activity in several different regions of Australia. Serosurveys provide convincing evidence that western grey kangaroos (WGK; Macropus fuliginosus) are commonly infected with the virus in south-west coastal regions of Western Australia. There is also evidence of seroconversions in WGKs coinciding with outbreaks of human disease. Such outbreaks have been preceded by favourable environmental conditions for breeding of WGKs, presumably leading to an increase in numbers of non-immune individuals in the environment. More recently, GIS analyses of clusters of human cases of RRV has shown a relationship between proximity of residence to mosquito and WGK habitat and risk of RRV disease. These findings indicate that monitoring of seroprevalence to RRV in vertebrate hosts of RRV, such as the WGK, may assist in predicting outbreaks of RRV disease and for determining whether strategies to manage natural host populations in close proximity to human habitation may be worth further consideration.

Global health security has become a major concern, particularly the threats to human and animal health from the emergence and re-emergence of epidemic-prone infectious diseases, as well as the significant and growing impact of these outbreaks on national and international economies. It has long been known that many of these diseases can cross the species barrier between humans, wildlife and domestic animals, and indeed over 70% of novel emerging infectious diseases are zoonotic, that is, have their origins in animal reservoirs. There have been many recent examples of this trend, the most dramatic being recently the SARS epidemic – the first major threat to global health from a novel zoonotic disease in the new Millennium. Other recent examples include the H1N1 influenza virus pandemic; the spread of Nipah virus into Bangladesh and India; and perhaps the most important of all, the ongoing concerns of a highly virulent influenza pandemic due to avian influenza virus (H5N1).

It is a privilege for all of us to present a brief tribute for the life of Geoffrey Shellam, an admired colleague and friend, to some for over 50 years. Geoff’s scientific intuition, his integrity and his scientific leadership were second to none.

The 2009 H1N1 influenza, initially known as swine flu, originated in North America in early 2009. This new strain of influenza A virus (H1N1) came to the attention of the international public health community when several foci of influenza-like illness were identified in Mexico, which had more than 850 cases of pneumonia, of whom 59 had died. Mild cases of influenza-like illness were also reported from Texas and California. Virus isolates were obtained from the cases in California and from samples of cases sent from Mexico to the Canadian National Public Health Laboratory in Winnipeg. Molecular analysis of these virus isolates showed that they were virtually identical and indicated that they represented a completely new, rapidly spreading strain of H1N1 virus, which appeared to have originated in swine. This was the first reassorted influenza virus to emerge since the 1968-1969 pandemic caused by the Hong Kong influenza virus. Under the new International Health Regulations (2005), this rapidly spreading, novel virus was quickly recognised by the World Health Organization as constituting a Public Health Emergency of International Concern, the first such emergency since the new International Health Regulations were introduced in mid-2007.

The term ?emerging diseases? has become synonymous with new, previously unknown infectious agents, or with known infectious agents which are either spreading geographically or increasing in incidence. An analysis by Jones et al (2008) showed that since 1940 there has been a steady increase in new diseases, and new diseases are continuing to emerge today. Most of these new diseases are of minor importance with respect to human or animal health, but occasionally important, highly pathogenic diseases arise, such as we have seen in recent years with SARS and Nipah virus, or with new variants or strains of known diseases such as avian H5N1 influenza, the current pandemic strain of H1N1 2009 influenza virus, and extremely drug resistant tuberculosis.

Nipah virus emerged in 1999 in Peninsula Malaysia, where it caused a severe respiratory disease in pigs, some of which also displayed encephalitic symptoms. Humans became infected following contact with infected pigs and suffered a severe encephalitic disease. There were a total of 276 human infections in Malaysia and Singapore, with 106 deaths, a case fatality rate of 38.4% 1. The outbreak was finally contained by culling just over one million pigs at significant cost to the Malaysian economy.

Since it was first raised more than 20 years ago, there has been increasing concern about the potential impacts of climate change on mosquito-borne viral diseases in Australia. This has generated a number of predictions and projections on the effect of global warming on the incidence and spread of Australian arboviruses. These have been discussed recently by Russell and Jacobs & colleagues and thus need not be repeated in detail here. In addition, it was also the topic of a previous ?In Focus? article. This paper will briefly focus on the complex interplay between climate-associated factors which may affect the incidence and spread of mosquito-borne viruses, and show how these factors may influence the ecologies of the major Australian arboviruses.

The Australian Biosecurity Cooperative Research Centre for Emerging Infectious Disease (AB-CRC) was a successful applicant under the Federal Government?s 2002 CRC programme, and will be formally established from July 2003. The aim of the AB-CRC is to protect Australia?s health, livestock, wildlife and economic resources by developing new capabilities to monitor, assess, predict and respond to emerging and exotic disease threats which impact on national and regional biosecurity. Emerging diseases are defined as those which are novel, previously unrecognised diseases, or those which are increasing in incidence or geographic range. The threats may be natural, accidental (such as an infected traveller) or deliberate (as in bioterrorism).