Predicting the potential distribution of Amblyomma americanum (Acari: Ixodidae) infestation in New Zealand, using maximum entropy-based ecological niche modelling.

Although currently exotic to New Zealand, the potential geographic distribution of Amblyomma americanum (L.), the lone star tick, was modelled using maximum entropy (MaxEnt). The MaxEnt model was calibrated across the native range of A. americanum in North America using present-day climatic conditions and occurrence data from museum collections. The resulting model was then projected onto New Zealand using both present-day and future climates modelled under two greenhouse gas emission scenarios, representative concentration pathways (RCP) 4.5 (low) and RCP 8.5 (high). Three sets of WorldClim bioclimatic variables were chosen using the jackknife method and tested in MaxEnt using different combinations of model feature class functions and regularization multiplier values. The preferred model was selected based on partial receiver operating characteristic tests, the omission rate and the lowest Akaike information criterion. The final model had four bioclimatic variables, Annual Mean Temperature (BIO1), Annual Precipitation (BIO12), Precipitation Seasonality (BIO15) and Precipitation of Driest Quarter (BIO17), and the projected New Zealand distribution was broadly similar to that of Haemaphysalis longicornis Neumann, New Zealand's only livestock tick, but with a more extensive predicted suitability. The climate change predictions for the year 2050 under both low and high RCP scenarios projected only moderate increases in habitat suitability along the mountain valleys in the South Island. In conclusion, this analysis shows that given the opportunity and license A. americanum could and would successfully establish in New Zealand and could provide another vector for theileriosis organisms.

Potential Spatial Distribution of the Newly Introduced Long-horned Tick, Haemaphysalis longicornis in North America.

The North American distributional potential of the recently invaded tick, Haemaphysalis longicornis, was estimated using occurrence data from its geographic range in other parts of the world and relevant climatic data sets. Several hundred candidate models were built using a correlative maximum entropy approach, and best-fitting models were selected based on statistical significance, predictive ability, and complexity. The median of the best-fitting models indicates a broad potential distribution for this species, but restricted to three sectors-the southeastern United States, the Pacific Northwest, and central and southern Mexico.

Using a rule-based envelope model to predict the expansion of habitat suitability within New Zealand for the tick Haemaphysalis longicornis, with future projections based on two climate change scenarios.

Haemaphysalis longicornis is the only species of tick present in New Zealand which infests livestock and is also the only competent vector for Theileria orientalis. Since 2012, New Zealand has suffered from an epidemic of infectious bovine anaemia associated with T. orientalis, an obligate intracellular protozoan parasite of cattle and buffaloes. The aim of this study was to predict the spatial distribution of habitat suitability of New Zealand for the tick H. longicornis using a simple rule-based climate envelope model, to validate the model against published data and use the validated model to project an expansion in habitat suitability for H. longicornis under two alternative climate change scenarios for the periods 2046-2065 and 2081-2100, relative to the climate of 1981-2010. A rule-based climate envelope model was developed based on the environmental requirements for off-host tick survival. The resulting model was validated against a maximum entropy environmental niche model of environmental suitability for T. orientalis transmission and against a H. longicornis occurrence map. Validation was completed using the I-similarity statistic and by linear regression. The H. longicornis climate envelope model predicted that 75% of cattle farms in the North Island, 3% of cattle farms in the South Island and 54% of cattle farms in New Zealand overall have habitats potentially suitable for the establishment of H. longicornis. The validation methods showed an acceptable level of agreement between the envelope model and published data. Both of the climate change scenarios, for each of the time periods, projected only slight to moderate increases in the average farm habitat suitability scores for all the South Island regions. However, only for the West Coast, Marlborough, Tasman, and Nelson regions did these increases in environmental suitability translate into an increased proportion of cattle farms with low or high H. longicornis habitat suitability. These results will have important implications for the geographical progression of Theileria-associated bovine anaemia (TABA) in New Zealand and will also be of interest to Haemaphysalis longicornis researchers in Australia, Japan, Korea and New Zealand.

Predicting the potential environmental suitability for Theileria orientalis transmission in New Zealand cattle using maximum entropy niche modelling.

The tick-borne haemoparasite Theileria orientalis is the most important infectious cause of anaemia in New Zealand cattle. Since 2012 a previously unrecorded type, T. orientalis type 2 (Ikeda), has been associated with disease outbreaks of anaemia, lethargy, jaundice and deaths on over 1000 New Zealand cattle farms, with most of the affected farms found in the upper North Island. The aim of this study was to model the relative environmental suitability for T. orientalis transmission throughout New Zealand, to predict the proportion of cattle farms potentially suitable for active T. orientalis infection by region, island and the whole of New Zealand and to estimate the average relative environmental suitability per farm by region, island and the whole of New Zealand. The relative environmental suitability for T. orientalis transmission was estimated using the Maxent (maximum entropy) modelling program. The Maxent model predicted that 99% of North Island cattle farms (n=36,257), 64% South Island cattle farms (n=15,542) and 89% of New Zealand cattle farms overall (n=51,799) could potentially be suitable for T. orientalis transmission. The average relative environmental suitability of T. orientalis transmission at the farm level was 0.34 in the North Island, 0.02 in the South Island and 0.24 overall. The study showed that the potential spatial distribution of T. orientalis environmental suitability was much greater than presumed in the early part of the Theileria associated bovine anaemia (TABA) epidemic. Maximum entropy offers a computer efficient method of modelling the probability of habitat suitability for an arthropod vectored disease. This model could help estimate the boundaries of the endemically stable and endemically unstable areas for T. orientalis transmission within New Zealand and be of considerable value in informing practitioner and farmer biosecurity decisions in these respective areas.

Monitoring an epidemic of Theileria-associated bovine anaemia (Ikeda) in cattle herds in New Zealand.

Monitoring an epidemic of an emerging vector-borne disease can be problematic; particularly in a country where vector-borne disease has previously had minimal impact on livestock. This paper describes methods of past and current surveillance of the Theileria-associated bovine anaemia (Ikeda; TABA) epidemic in New Zealand, and the resulting inferences made. Over the three year period of the TABA epidemic a portfolio of surveillance methods has been used: case reporting (with subsidised PCR testing), syndromic surveillance, sentinel surveillance, testing convenience samples for herd infection, as well as specific active surveillance initiatives to understand the tick vector distribution. Surveillance data have shown that the number of affected cattle herds has continued to increase over time with seasonal peaks in spring and autumn coinciding with peak activity of nymph and adult ticks respectively. In spring 2014, the epidemic extended south into areas that were previously considered to be unsuitable for the tick vector. As a result a survey was initiated that showed that ticks were present in areas outside of the known distribution. Testing pooled blood samples from cattle herds across New Zealand showed there still remained a significant percentage of herds where only non-Ikeda type infections were present, indicating that these herds were at risk of future TABA (Ikeda) outbreaks. For some regions there had been a noticeable increase in the percentage of herds infected, yet with only a small increase in the number of outbreaks compared with the previous year. Thus, outbreaks had either gone unobserved or had not been confirmed by testing. In these regions extensive low-input beef farming could explain the non-detection observed. There was a close relationship between the number of syndromic reports of anaemia and the number of confirmed cases of TABA (Ikeda), (P<0.01, adjusted R-squared=0.74). Active monitoring of the epidemic for a three year period has provided valuable insight into seasonal nature of the disease and its continuing impact. Information from multiple surveillance sources can help build up an understanding of the epidemiology, even when data from each individual surveillance stream are limited. The TABA (Ikeda) epidemic in New Zealand represents a useful case study of long term monitoring where disease is caused by an emerging pathogen.

Control of the sheep blowfly in Australia and New Zealand--are we there yet?

The last 50 years of research into infections in Australia and New Zealand caused by larvae of the sheep blowfly, Lucilia cuprina, have significantly advanced our understanding of this blowfly and its primary host, the sheep. However, apart from some highly effective drugs it could be argued that no new control methodologies have resulted. This review addresses the major areas of sheep blowfly research over this period describing the significant outcomes and analyses, and what is still required to produce new commercial control technologies. The use of drugs against this fly species has been very successful but resistance has developed to almost all current compounds. Integrated pest management is becoming basic to control, especially in the absence of mulesing, and has clearly benefited from computer-aided technologies. Biological control has more challenges but natural and perhaps transformed biopesticides offer possibilities for the future. Experimental vaccines have been developed but require further analysis of antigens and formulations to boost protection. Genetic technologies may provide potential for long-term control through more rapid indirect selection of sheep less prone to flystrike. Finally in the future, genetic analysis of the fly may allow suppression and perhaps eradication of blowfly populations or identification of new and more viable targets for drug and vaccine intervention. Clearly all these areas of research offer potential new controls but commercial development is perhaps inhibited by the success of current chemical insecticides and certainly requires a significant additional injection of resources.

Flystrike in New Zealand: An overview based on a 16-year study, following the introduction and dispersal of the Australian sheep blowfly, Lucilia cuprina Wiedemann (Diptera: Calliphoridae).

A summary and analysis have been carried out on data from over 6000 instances of flystrike in sheep in NZ, over a 16-year period, using a self-referral system where farmers submitted larvae and related information. The study covered a period of establishment and subsequent countrywide spread of the exotic blowfly, Lucilia cuprina. Comparisons are drawn between flystrike as it was perceived by surveys carried out before the 1940s, and the current situation with L. cuprina as an added major impediment. Briefly, the main differences are an increase in the prevalence of flystrike, changes in the representation and relative influence of individual primary blowfly species, an extension of the flystrike 'season', and an apparent increase in the importance of footrot as a factor predisposing to flystrike. Otherwise, flystrike is still primarily a disease of ewe lambs that are struck predominantly around the tail and perineum, mainly because of faecal staining.

Germ-line transformation of the Australian sheep blowfly Lucilia cuprina.

The Australian sheep blowfly, Lucilia cuprina, is the most important economic insect pest for the sheep industries in Australia and New Zealand. piggyBac-mediated germ-line transformation of L. cuprina was achieved with a helper plasmid that had the Drosophila melanogaster hsp70 promoter controlling expression of the transposase and a piggyBac vector with an EGFP marker gene. Two transformant lines were obtained, at a frequency of approximately 1-2% per fertile G0. One of these lines has a single copy of the transgene, the other most likely has four copies. This is the first report of germ-line transformation of L. cuprina and is an important step towards the generation of engineered strains that would be suitable for male-only release eradication/suppression programmes.

Distribution, seasonality and relative abundance of Stomoxys calcitrans (stablefly) (Diptera: Muscidae) in New Zealand.

AIMS: To determine the current distribution, seasonality and relative abundance of Stomoxys calcitrans in New Zealand in order to provide information that could be used to assess risks of transmission of equine infectious anaemia (EIA). METHODS: Adhesive yellow traps were distributed to schools throughout New Zealand and used to detect the presence of S. calcitrans between November 1999 and April 2000 at sites considered likely to be a focus for S. calcitrans breeding and activity. In addition, researchers undertook monthly trapping at six other sites between August 1999 and June 2000 to measure the duration and seasonal periodicity of S. calcitrans flight activity. Veterinary practices and farmers were also surveyed to provide anecdotal evidence of the presence or absence of S. calcitrans, particularly in areas where no flies were trapped by schools. RESULTS: Stomoxys calcitrans was found to occur in both North and South Islands, but principally in locations where dairy farming occurred. The fly was active during most months of the year, except perhaps during July and August, and was particularly active in warmer North Island districts such as the Waikato. Peak activity was recorded from January to May. The fly was more abundant in Northland, Auckland, Waikato, the Marlborough Sounds and Nelson than in other districts, as determined by the number of occasions flies were caught relative to the number of traps set. There are only a few areas, such as around Taupo, the Otago Lakes, Central Otago and the Mackenzie Basin, where S. calcitrans was not trapped or, on the basis of anecdotal evidence, thought not to occur. CONCLUSIONS: Given that other potential vectors of EIA are absent from New Zealand, Taupo, the Otago Lakes, Central Otago and the Mackenzie Basin districts could be considered areas of low risk for EIA transmission to horses. In addition, teachers and school children were capable, in most instances, of supporting a nationwide survey providing the methods were simple and the aims few.