The PICO literature review process [25] was applied to formulate search terms to be used on literature databases by extracting keywords based on the aims using four components: population or problem, intervention or exposure, comparison, and outcome. Details of the PICO process used are detailed in Supplementary 1.

This literature review did not limit search results to any specific geographical area or year range. The literature review included literature written in any language. The investigators for this literature review were able to read and validate contents of literature written in English, French, Spanish, Portuguese, and Japanese. Literature written in other languages were reviewed provided accurate machine translation was available. Grey literature, including unpublished and pre-print articles, were also included in this review. The following study types were included in the literature review: observational, cohort, spatial epidemiology, mapping, and mathematical modelling.

The following search terms were included in database searches with the NOT Boolean operator and searching only in titles and abstracts: clinical trial, randomised control trial, vaccination, vaccine, genomic, genome, phylogeny, and biochemical.

This literature review searched for available literature using five databases: PubMed, Scopus, Web of Science, Europe PMC, and the University of Queensland library website. All five databases were searched, and their results were recorded on 6 March 2023. The keyword searches used are detailed in Supplementary 1.

Search results were first screened for duplicate results as detailed in the PRISMA flowchart (Figure 1) [26]. The remaining results were then screened based on titles and abstracts, to ensure that contents of the results relate to at least one of the aims of the literature review. The number of results that were discarded as a result of each screening process was recorded, along with the reasons for exclusion.

All search results were recorded in EndNote software, and data retrieval for full-text reviewed papers was conducted using a Microsoft Excel spreadsheet (Supplementary 2).

Articles that passed the screening stage were read in full to assess the relevance of their contents, as well as the validity of their study methods and results.

LSD was first recorded in Zambia in 1929 [7]. Since then, LSD has spread through Africa, including Kenya [10], Nigeria [53], Ethiopia [1, 8, 27, 30, 38, 41, 43], Uganda [66, 68], South Africa [37], and Egypt [37, 51, 77]. LSDV infections have also been detected sporadically in parts of the Middle East (since 1989) and Europe and Asia (since 2015), including Albania [52, 61], Greece [13, 64], Bulgaria [13, 64], North Macedonia [13, 64], Kazakhstan [47], Russia [13, 14], Armenia [13], Türkiye (formerly Turkey) [5, 7, 13, 14, 29, 46, 61, 78], Israel [13, 51, 74, 84], Lebanon [7], Jordan [7, 13, 28], Iraq [7, 29], Saudi Arabia [13], and Oman [80]. Since 2019, the disease has emerged in South and South-east Asia, including large outbreaks reported in India [6, 33, 35, 60, 69], Bangladesh [6, 33, 35, 60], Pakistan [6, 45, 50], Sri Lanka [33, 35], China [4, 45, 57], Hong Kong [6], Taiwan [33, 57], Bhutan [6, 33, 35], Nepal [6, 33, 35, 60], Vietnam [6, 14, 33, 35, 60], Laos [14, 35], Cambodia [14, 35], Myanmar [6, 14, 33, 35, 60], and Thailand [6, 7, 14, 33, 35, 64]. Additionally, while no reports were contained in the results of the literature review, LSDV was first reported in Indonesia in March 2022 via the World Organisation for Animal Health, and most recently in East Java in December 2022 [18, 85]. A number of countries are still considered to be LSD-free, including Australia and the United Kingdom [86].

Mosquitoes were first implicated as a possible vector for LSDV following an LSDV outbreak in Kenya in 1959 due to the infestation of Culicidae species in the outbreak areas [10, 70]. The first experimental test to confirm biting insects as a LSDV vector found A. aegypti to be an efficient vector, with the species being able to transmit LSDV to cattle up to 6 days following feeding on LSDV-infected cattle. This and subsequent studies have suggested that LSDV may not replicate in infected insects, including A. aegypti, indicating only mechanical transmission [10, 11, 70]. However, the significance of A. aegypti in LSDV transmission in the field has been questioned due to this species displaying a preference to biting humans [70].

The biting insects found to have the greatest potential for LSDV transmission are A. aegypti mosquitoes and stable flies (S. calcitrans). Other Stomoxys spp. (S. sitiens and S. indica), horseflies (Haematopota spp.), biting midges (Culicoides nubeculosus), and ticks (Rhipicephalus (Boophilus) decoloratus, Rhipicephalus appendiculatus, Rhipicephalus annulatus, and Amblyomma hebraeum) also represent possible vectors [10, 11, 13, 42, 48, 49, 54–56, 64, 65, 71, 73, 79, 82]. Recent experimental studies have highlighted that S. calcitrans has a high reproduction ratio, is capable of retaining LSDV for at least 3 days, and is capable of mechanical transmission of LSDV to cattle [11, 48, 71, 79]. While there is only limited evidence for the biting midge C. nubeculosus as a potential vector for LSDV transmission, Culicoides spp. are reported to be common on cattle farms and therefore may pose a serious risk of LSDV transmission if they are proved to be efficient vectors of LSDV [11]. Various modes of LSDV transmission have been reported in different species of ticks: R. decoloratus (transstadial and transovarial), R. appendiculatus (mechanical, intrastadial, and transstadial), R. annulatus (transovarial), and A. hebraeum (mechanical, intrastadial, and transstadial) [7, 54–56, 73, 81, 82]. The detection of LSDV in the eggs of LSDV-infected R. decoloratus ticks is important because the eggs of this species are reported to be able to develop in soil and vegetation and thus present a risk of environmental contamination with LSDV-infected ticks [7, 81, 87]. Furthermore, experimental evidence has demonstrated that LSDV infection in female R. decoloratus ticks persisted following exposure to simulated winter conditions of 5°C at night and 20°C during the day for 2 months, with LSDV being detected in subsequently laid eggs [55]. This suggests that the virus may be able to over-winter in these tick species, which provides a possible means for LSDV to persist in the environment during colder months when biting insects are less active. In a field study of ticks collected from infected cattle during LSD outbreaks in Egypt and South Africa, LSDV was detected in a large proportion of different tick species, including R. appendiculatus, A. hebraeum, and Rhipicephalus (Boophilus) spp. [83]. These field and experimental findings provide evidence of ticks playing a potentially important role in the transmission of LSDV. In particular, the transovarial transmission of LSDV in certain tick species, combined with their short life cycle, indicates that they may act primarily as LSDV reservoirs rather than LSDV vectors [70].

Evidence suggests that approximately half of cattle infected with LSDV are asymptomatic, and that vectors are still capable of acquiring LSDV from these cattle [7]. Another study found that as few as four or five cattle in an LSDV infected herd of 100 head may show symptoms of LSD [64]. Due to lower viral titres, mechanical transmission of LSDV by vectors from asymptomatic cattle may be less efficient than that of clinically affected animals. One experimental study on mechanical transmission of LSDV from infected A. aegypti to cattle using one Holstein–Friesian steer and five Angus cross Jersey steers observed that one of the six cattle showed no clinical signs of LSD despite LSDV being detected in a blood sample from the animal; however, this study did not specify the breed of the sub-clinical steer [10]. Another experimental study, which tested mechanical transmission of LSDV from A. aegypti, Culex quinquefasciatus, S. calcitrans, and C. nubeculosus to eight male Holstein–Friesian cattle, classified five out of the eight cattle as being sub-clinical [11]. Both of these results may not accurately reflect the true incidence of sub-clinical LSDV infection in cattle due to their experimental nature.

Another potential factor influencing LSDV transmission is the fact that LSDV can survive in the skin lesions and scabs of cattle from 25 to 50 days to several months, making transmission still possible after other clinical signs of LSDV infection have subsided [7, 14, 44, 64]. Although direct contact is generally thought to be a less efficient means of LSDV transmission, exposure to nasal, lachrymal, and pharyngeal secretions may contribute to LSDV transmission, with LSDV able to survive up to 11 days in saliva [37, 77]. Additionally, LSDV has been reported to survive up to 42 days in fresh semen [39], and there are reports of LSDV being detected in semen excreted from bulls that have already recovered from the disease [39]. Experimental evidence has shown that LSDV transmission is possible during artificial insemination using LSDV-infected fresh semen [39].

A number of factors can influence LSDV exposure and infection in cattle in endemic countries, including weather, physical environment, sociocultural factors, and inadequate biosecurity control interventions.

(1) Probability of Introduction. Live animal movement by both legal and illegal means provides opportunities for the transmission of LSDV. A recent study suggested that this was more likely to contribute to the wide geographical spread of LSDV infection, than mechanical transmission via vectors [7]. Most LSD-free countries have implemented WOAH recommendations on preventing trans-boundary spread of LSD; however, these interventions have become difficult to enforce in some instances, including on the European Union (EU) border [36]. The emergence of LSD in China in 2019 can be partly explained by cattle movement from neighbouring LSD endemic countries into China [4]. A study exploring the risk of introduction of LSD into the United Kingdom (UK) through legal importation of skins, hides, and wool from the EU found that the probability of LSD being introduced by a single hide/skin/wool bale from an EU member state where LSD outbreaks are ongoing was low [40].

(2) Probability of Detection. While EU member state reference laboratories are able to detect LSDV, it is up to farmers and veterinarians to first recognise any clinical signs of LSD in newly imported cattle in the field before their infection status can be confirmed in a laboratory. However, this can be challenging during the early stages of infection because LSD clinical signs can be confused with clinical signs of other diseases and cattle may not be monitored daily. The fact that many LSDV infections are asymptomatic, combined with the challenges associated with detecting and diagnosing LSDV infection in a timely matter in the field, makes it difficult to control transmission of LSDV to vectors and cattle. These factors can render any culling of LSD-infected cattle and those they have been in contact with ineffective as the virus may have already dispersed from the point of detection.

A wide range of LSD control strategies have been implemented in LSD endemic countries, including vaccination, restriction of cattle movement, culling of infected and exposed cattle, and vector control [13, 37].

Registration of cattle movement, as part of surveillance and monitoring, has been implemented in a number of LSD-free countries. In Switzerland, it is a legal requirement for all premises keeping cattle to be registered, as well as for all cattle movement and culling to be reported within 3 working days to the Swiss cattle movement database (Tierverkehrsdatenbank, TVD). This timely monitoring of cattle movement allows for rapid contact tracing of cattle, especially when potentially infected cattle are still in the incubation period [44]. Ukraine also has strict laws in place for LSD prevention, whereby the importation of cattle and biomaterials, such as hides and semen, are only allowed from LSD-free countries, where surveillance and monitoring systems are in place. While a strong national LSD prevention strategy is in place, it is not clear whether current farm-level biosecurity measures and farmers’ awareness of LSDV infection are sufficient to respond to LSDV incursions in their herds [39].

The UK has a comprehensive LSD control strategy, which sets out clear and specific actions to be taken in the event of a suspected or confirmed case of LSD in the country. The control strategy outlines the steps to be taken to report and diagnose/confirm suspected LSDV infection, response activities including culling, cleansing and disinfection (including vector control at infected premises), and contact tracing, establishment of disease control zones for movement and trade restriction, monitoring and surveillance of live animals, possible deployment of vaccination, a recovery plan for the control zones, and the process for resuming international trade and regaining disease-free status. This document provides advice for governments, industries, and individuals involved with LSD susceptible animals [91].

Fourteen articles that presented a number of different epidemiological modelling approaches were identified [5, 11, 31, 32, 34, 42, 58, 59, 62, 63, 67, 72, 75, 76]. These studies have applied epidemiological modelling to various aspects of LSDV infection and transmission to support decision making in designing and implementing LSD control strategies.

A number of common themes were identified in the 47 reviewed articles relating to risk factors for LSDV exposure and infection in cattle in endemic countries. First, environmental factors shown to increase the risk of LSDV infection in cattle included high average daytime temperature, high rainfall, and close proximity to water bodies. These weather characteristics and physical environmental properties correspond to the ideal conditions for vector activity and cattle exposure to vectors. Furthermore, stable flies are known to be able to travel long distances (up to 29 km in laboratory tests [84]), with this distance being potentially further extended by strong wind patterns, and marked flies having been recaught up to 83 km from their point of release [84]. However, there is no direct evidence of LSDV transmission by stable flies that have travelled long distances [37, 38, 43, 51, 61, 65, 69, 77, 78, 84]. Second, in LSD endemic countries, the practices of communal grazing and communal water points are common. This mixing of herds presents the possibility of exposure to LSDV both via vector transmission and exposure to nasal, lachrymal, and pharyngeal secretions [1, 27, 37, 41, 65, 66, 68, 69, 77]. Third, awareness among farmers regarding LSDV transmission, along with the degree to which farm-level biosecurity practices are implemented throughout the country, is also reported as important risk factors in some LSD endemic countries. This may in turn be hampering efforts to control the spread of LSDV infection in these countries [4, 8, 30, 47, 53]. Fourth, environmental contamination by LSDV-infected tick eggs in soil and vegetation has been reported, and experimental evidence suggests that LSDV infection can persist in female R. decoloratus ticks under simulated winter conditions; however, there is limited evidence of how important a role ticks play in the transmission of LSDV [7, 55]. Fifth, LSDV transmission through cattle movement occurs as a result of illegal trade, as well as large-scale movement of animals including cattle following cultural events and migration of refugees due to political unrest. Cattle movement is thought to be the main factor in the large geographical spread of LSDV [5, 7, 45, 50]. Finally, while vaccination has been effective in controlling the spread of LSDV in endemic countries, the only currently available vaccines are live-attenuated vaccines, which cannot be used as a preventative measure in LSD-free countries without the risk of international trade restrictions remaining [7, 13, 57, 91]. Additionally, there have been reports of vaccine-like recombinant strains of LSDV in Asia, with studies suggesting that these strains may have risen from the use of poorly manufactured LSDV vaccines [94]. These findings highlight the need for control measures in the deployment of LSDV vaccines.

The inclusion and exclusion criteria applied to the literature search used in our review were devised to extract key data that would assist in the development of spatial epidemiological disease modelling; however, these may have limited the scope of risk factors identified. Broader inclusion criteria may have helped identify additional risk factors, which may have helped in describing the effects of the risk factors identified in this review.

To date, a limited number of studies have presented mathematical models estimating the potential risk of LSDV transmission from possible vectors, with LSDV infection in cattle by stable flies and A. aegypti mosquitoes in particular showing a potentially high reproduction ratio. All modelling studies related to spatio-temporal distribution of LSDV infection risk, including time-series forecast models, cluster analysis, and spatio-temporal modelling and risk mapping, were based on data from LSDV endemic countries [5, 11, 31, 32, 34, 42, 58, 59, 62, 63, 67, 72]. These studies’ findings confirmed the important climate risk factors of higher temperature and rainfall, as well as identified geographical areas most at risk of LSDV outbreaks occurring, along with when they are most likely to occur. The only studies from LSD-free countries describing epidemiological approaches for modelling risk of LSDV importation were from France, and their focus was on probabilities of LSDV entering the country via different methods, including importation of infected live cattle and infected vectors being moved on vehicles transporting livestock into the country [75, 76]. The literature review did not identify any studies applying multi-criteria decision analysis modelling to look at the suitability of LSD-free countries for LSDV incursions, such as distribution of cattle population and climate and habitat factors necessary for the establishment of infected vectors.

Based on the reviewed literature, the Australian landscape presents a wide range of biotic and abiotic optimal conditions for LSDV incursion and spread. The populations and species of vectors present in different parts of Australia may vary, and therefore, understanding the distribution of competent vectors in Australia will be valuable in identifying areas at potentially high risk of LSDV transmission in the event of introduction of LSD into Australia. In addition, there is considerable arthropod-borne viral (arboviral) activity in northern Australia that is monitored through the National Arbovirus Monitoring Program (NAMP) for livestock viruses of interest to key export markets, such as bluetongue virus, Akabane, and bovine ephemeral fever virus. It would seem prudent to expand this programme to include LSDV surveillance in this well-established system to increase the likelihood of early detection of any incursion by the virus [95].

Available literature describes R. decoloratus as having potential for transovarial transmission of LSDV and being able to survive winter conditions. While its short life cycle may limit its ability for rapid spread of LSDV, this species may act as an LSDV reservoir [55, 70]. The Australian cattle tick, R. australis, is reported to be closely related to R. decoloratus [18, 96, 97]. While members of the Rhipicephalus genus, including R. australis and R. decoloratus, are known vectors of other important livestock pathogens such as Babesia bovis, Babesia bigemina, Anaplasma marginale, and Theileria parva [98], recent studies have reported a much wider repertoire of viruses being detected in ticks of potential importance to mammalian host species [98, 99]. Future studies are warranted to investigate the ability of the Australian cattle tick to act as a vector for mechanical transmission of LSDV or as a reservoir of LSDV. These studies should also evaluate the capacity of R. australis to vertically transmit LSDV, as has been demonstrated for R. decoloratus [81]. Vertical transmission would be the most important mode of R. australis-mediated transmission of LSDV, as it completes its life cycle on a single host, thus negating direct horizontal host transmission.

Another potential source of LSDV entering Australia is via migratory birds through the East Asian–Australian migratory flyway. The bird species using this flyway have been of interest with respect to avian influenza [100]. Critical points of difference between avian influenza and LSDV are that birds are considered to be the natural reservoir of influenza viruses and they are not susceptible to LSDV infection. As such, for migratory birds to play a role in an LSDV incursion into Australia, it would need to be via carriage of a suitable vector, such as ticks. As described previously, bird–tick interactions have been proposed as a possible source of long-range movement of LSDV [35]. While this possibility cannot be excluded as a potential source of LSDV incursion into Australia, it is considered unlikely as there is no overlap of tick species between Australia and countries such as Indonesia, with no evidence of new tick species entering and becoming established in Australia in recent history [101].

Previous LSD outbreaks in Israel were thought to have been due to the long-range dispersal of LSDV-infected vectors from Egypt being carried by strong wind patterns [51]. A similar precedent exists in Australia, where Culicoides biting midges infected with bluetongue virus are thought to have been blown into the top end of the Northern Territory from overseas by warm humid winds. These winds can reportedly carry insects several hundred kilometres [102]. This suggests that LSDV-infected vectors could potentially also be transported into the north of Australia from neighbouring countries via wind currents.

Intrinsically, linked to the availability of a suitable vector(s) for LSDV in Australia is host susceptibility. Given the proximity of the northern Australia cattle production systems to countries where LSDV is currently circulating, it is reasonable to conclude that it is the most likely incursion point from non-anthropologic means. There is likely to be variable susceptibility to LSDV among Australian cattle herds. This variability may be driven by the gradient of Bos indicus dominant genetics to B. taurus dominant genetics from across northern Australia down the eastern states through to the southern production systems [103]. While this genetic gradient is largely driven by the capacity of B. indicus genetics to be productive in the harsher environments of tropical and sub-tropical Australia, it may also make the detection of LSDV incursions problematic. It is widely accepted that B. indicus breeds have increased innate resilience to LSDV infections compared to European B. taurus breeds [104, 105]. Recently, Sudhakar et al. [106] reported on LSDV outbreaks in India with overall 7.10% morbidity (range: 0.75%–38.34%) and 0% mortality in cattle (n = 2,539) from five locations. The cattle (n = 133) from the location with the highest morbidity, an organised farm, had a mixed breed population consisting of B. indicus, B. taurus, and B. indicus × B. taurus, though the specific breakdown of the numbers of cases for each breed was not reported [106]. As noted by the authors, while breed was likely to be an important factor in the variable morbidity rates and lack of mortality, the virulence of the LSDV strains at each location may have also contributed to these results [106]. It is also worth noting that some indigenous B. taurus breeds (e.g., Egyptian Baladi cattle) are reported to have reduced LSDV susceptibility compared to European B. taurus breeds [77].

Consequently, there could be two outcomes in the event of an LSDV incursion into this region. First, as a result of the B. indicus genetics in this production system, these cattle may naturally resist a low-level outbreak. While this might be considered a desirable outcome from a trade perspective, it could mean potential incursion points are not identified in a timely manner to allow the implementation of appropriate management controls. Second, the natural resistance of these breeds may suppress the expression of clinical signs, making the timely identification of affected animals more problematic in the early stages of infection, potentially exacerbating the outbreak prior to its detection. Although as described previously, pre-clinical and sub-clinical infections may be less likely to facilitate vector-borne transmission [11]. Potentially further confounding these outcomes are feral populations of buffalo and, to a lesser extent, feral cattle, in northern Australia that are likely to be susceptible to LSDV. By the very nature of these herds, early detection of LSDV, let alone control or eradication, is likely to be highly problematic.

With the recent detection of LSD in countries neighbouring Australia to its north, such as in Indonesia, the risk of importation of LSD into northern Australia is considered non-negligible. The existing strict biosecurity measures in place effectively reduce the risk of importation of LSD via infected animals or related products, with restrictions on the countries of origin. The Australian Government Department of Agriculture, Fisheries and Forestry regulates the importation of reproductive materials, such as bovine semen, with strict rules and procedures in place to prevent the introduction of diseases into Australia’s animal populations [107]. However, the risk of importation via infected insects entering through international ports or travelling over sea into northern Australia is considered high. The Australian Government has strict biosecurity measures in place at all international ports to minimise the risk of infected animals or materials entering the country; however, it also needs to ensure a high level of awareness of LSDV is maintained among farmers, veterinarians, and other related individuals. Disinsection is conducted at international ports; however, it is suggested that development of insecticide resistance by vectors may increase the risk of importation of LSDV into Australia via infected vectors. Australia has developed a nationally agreed policy for controlling LSD in a timely manner in the event of a suspected or confirmed case of LSD in the country [18]. Australia’s animal health surveillance system enables the early detection of LSD. In particular, the Northern Australia Quarantine Strategy (NAQS) has implemented routine testing of both domestic and feral animals for LSD in Northern Territory, Queensland (including the Torres Strait), and Western Australia [17]. Biosecurity measures, including both preventing LSDV entering the country and controlling LSDV infections in the event of an incursion, are important in preventing and mitigating the potential economic impact on Australia’s cattle industries. An example of a disease affecting cattle and impacting national economies is a foot and mouth disease (FMD), where outbreaks in other countries have impacted dairy production in cattle, resulting in economic losses due to restrictions on exports of dairy products [108]. A previous study modelled the potential economic impacts of FMD entering Australia and estimated that there would be significant losses, in terms of both national cattle production and export earnings, in the event of an outbreak in the country [95]. In the first year of the outbreak, the economic impact was estimated to be 0.6% of gross domestic product (valued at AUS$3.5 billion in 1999–2000) and 0.8% drop in employment, highlighting the need for government and industry cooperation in the prevention and control of FMD [109]. More recent modelling has estimated the total direct economic impact of an FMD outbreak in Australia at AU$80 billion (2020–2021 AUD) over 10 years [110].

The Australian control strategy provides more specific recommendations on controlling the spread of LSD, such as vector management, with an emphasis on the need for responses that are tailored to the various environmental conditions and seasons in Australia [18]. In addition to this control strategy, Australia has set out an action plan to actively take steps to strengthen preparedness for a potential introduction of LSD into the country. The plan has set a number of actions to achieve this, under the objectives of developing international engagement, border biosecurity and trade, diagnostic capability and capacity, surveillance, preparedness and response, awareness and communications, research and innovation, and recovery. As part of this preparedness plan, Australia is supporting Indonesia’s LSD outbreak response and is helping to improve technical and diagnostic capability and surveillance [111].

The most common practice for control of LSDV in endemic countries has been extensive vaccination programmes in cattle, using live-attenuated vaccines. However, this is not a practical preventative measure in LSD-free countries such as Australia as DIVA principles cannot be used to distinguish vaccinated animals from infected animals. As such, the use of live-attenuated vaccines could prolong the potential economic impact of an outbreak through continuation of international trade restrictions.

However, Australia’s action plan sets out priorities aimed to enhance Australia’s ability to prevent, detect, prepare for, and respond to a possible LSDV incursion. Activities in the plan include developing a national cattle vaccination strategy and modelling systems for LSD. The plan highlights the importance of being able to map and model cattle populations and movements through resources such as the Australian National Livestock Identification System (NLIS, a lifetime cattle movement database) to support LSD surveillance and preparedness activities [111]. The capacity of the NLIS database to inform the effective tracing of cattle movement and mixing with respect to modelling disease risk has previously been demonstrated [112].

Recently, qualitative and quantitative risk assessments of four specific unregulated pathways for entry of and exposure of LSDV in Australia were performed: (1) wind-borne dispersal of arthropod vectors, (2) commercial vessels carrying hitchhiker arthropod vectors (excluding live export vessels), (3) returning live export vessels carrying hitchhiker arthropod vectors, and (4) Torres Strait Treaty movements carrying hitchhiker arthropod vectors [22, 23]. The risk assessments developed a parameterised model, based on evidence collected via consultation with experts and a literature review, to evaluate three different scenarios: (1) at least 30–50 insects are necessary for successful vector-to-bovine transmission of LSDV, (2) several (i.e., 3–5) vectors are necessary for transmission, and (3) a single insect is sufficient for transmission, and estimated incursion risk using a two-dimensional Monte Carlo simulation. The estimated risk for the first two scenarios was negligible to very low, with a substantially increased risk in the third scenario; however, the risk assessment noted that this third scenario has not been achieved experimentally. The highest risk pathway was found to be the wind-borne dispersal of infectious vectors, with the highest likelihood of LSDV incursion associated with areas within the Northern Australian Quarantine Strategy (NAQS) risk zones, including the Tiwi Islands and regions east of Darwin, extending to and including the Cobourg Peninsula. These findings support those of studies, which suggested that LSDV-infected stable flies from Egypt may have introduced LSDV into Israel as a result of strong wind patterns [51, 84].

Importantly, there were significant uncertainties in the model parameters due to lack of data availability (e.g., numbers of herds symptomatically infected with LSDV overseas), lack of consensus among experts on probability estimates (e.g., infectious vectors being able to successfully travel via wind), and the use of proxy data (e.g., urbanisation index as a proxy for the likelihood that an infectious vector would travel to a seaport in the country of origin) [22]. Consequently, the risk assessments emphasise that the results do not accurately represent the true risk of LSDV incursion into Australia. Future experimental studies could be designed to more accurately measure these parameters.

The risk assessments also suggest that the risk of LSDV incursion into Australia may be increasing due to climate change. In particular, this is thought to have led to an increase in the frequency of suitable meteorological conditions for wind-borne vector dispersal and changes to the Australian environment that have expanded the areas favourable for LSDV vector activity over recent years [23]. Presently, modelling has only explored the risk of an LSDV incursion into Australia; however, these need to be supplemented by models that incorporate such environmental changes to identify the geographical areas with the highest potential for the spread of LSD in the Australian cattle population following an LSDV incursion in order to support risk-based surveillance of LSD in Australia.

The Australian Government National LSD Action Plan highlights the need for developing modelling tools that can quickly assess the changing risk profile of LSD. Furthermore, the action plan draws attention to the Australian Animal DISease (AADIS) model, which can simulate the spread and control of animal disease in Australia, and that there is a need for the development of such tools to predict appropriate controls for LSD [111].