Old World Screwworm Research Articles

Invasion of the Land of Samurai: Potential Spread of Old-World Screwworm to Japan under Climate Change

Temperatures have fluctuated dramatically throughout our planet’s long history, and in recent decades, global warming has become a more visible indicator of climate change. Climate change has several effects on different economic sectors, especially the livestock industry. The Old-world screwworm (OWS), Chrysomya bezziana (Villeneuve, 1914), is one of the most destructive insect pests which is invading new regions as a result of climate change. The economic loss in livestock business due to invasion of OWS was previously assessed by FAO in Iraq to be USD 8,555,000. Other areas at risk of invasion with OWS in the future include Japan. Therefore, maximum entropy implemented in MaxEnt was used to model predictive risk maps of OWS invasion to Japan based on two representative concentration pathways (RCPs), 2.6 and 8.5, for 2050 and 2070. The Area Under Curve (AUC) indicates high model performance, with a value equal to 0.89 (±0.001). In addition, the True Skill Statistics (TSS) value was equal to 0.7. The resulting models indicate the unsuitability of the northern territory of Japan for invasion by OWS. The main island’s southern costs show high and very high invasion suitability, respectively, and both Kyushu and Okinawa are at high risk of invasion with OWS. The predicted risk maps can be considered a warning sign for the Japanese quarantine authority to hasten a control program in order to protect the livestock industry from this devastating pest.

Epidemiology of traumatic myiasis due to Chrysomya bezziana in Indonesia

<p>Epidemiology of traumatic myiasis in Indonesia was studied by the widespread collection of fly larvae from infested livestock in passive case detection surveys involving veterinary clinics. In addition, monthly data from Kediri regency in Eastern Java were analysed from 2006-2009 to explore the seasonality of myiasis. Larvae from a total of 260 cases from the nationwide survey and 341 cases from Kediri were identified. Except for 5 cases of chicken infestation due to Musca species in the nationwide survey, all other cases were exclusively caused by the Old World screwworm (OWS) fly, Chrysomya bezziana (Diptera: Calliphoridae). The monthly numbers of cases at Kediri were very variable, with cases in all months, but there was statistical evidence for an increase in cases in January and December, during the rainy season. The greatest numbers of infestations recorded were from cattle and goats. The most frequently infested sites nationwide and in Kediri were the vulva and umbilicus, associated with calving, which is a major risk period for traumatic myiasis. Mitochondrial DNA typing of 176 specimens was useful for detecting multiple infestations, but no association was found between genetic lineage and host. The equatorial climate of Indonesia, combined with poor husbandry systems are factors that help to support OWS fly development year round. Even if not considered a disease of strategic importance, screwworm myiasis remains a threat to livestock production in Indonesia and a major welfare issue that requires constant interventions by farmers. The new and collated epidemiological data presented represent the most extensive survey of traumatic myiasis in Indonesia to date and provide a valuable baseline to support integrated pest management programs.</p>

Prophylactic and therapeutic efficacy of Australian-registered insecticide formulations against Old World screwworm (Chrysomya bezziana) infestation.

To determine the prophylactic and therapeutic efficacy of Australian-registered insecticide formulations against Old World screwworm (OWS) myiases for potential use in screwworm containment and eradication programs. The longevity of protection provided by six insecticidal formulations (subcutaneous ivermectin, doramectin and abamectin, a topically applied aqueous formulation of spinosad, ivermectin controlled-release capsule and a dicyclanil spray-on formulation) was tested using implants of 1st-instar OWS larvae on Javanese thin-tail sheep. Therapeutic efficacy of four formulations (topical ivermectin, chlorfenvinphos/cypermethrin mixture, aerosol spinosad formulation and a formulation containing propetamphos and eucalyptus oil) was tested against 2- and 4-day-old OWS strikes. Both the ivermectin capsule and dicyclanil spray-on formulation gave 100% protection against screwworm implants for the full 12 weeks of the study. Ivermectin, doramectin and abamectin administered SC all gave 100% protection at 3 days post-treatment, but at 2 weeks the protection had become incomplete. Spinosad dipping did not give complete protection at any time. All four therapeutic treatments gave complete resolution of 2-day-old strikes and topical ivermectin, spinosad and chlorfenvinphos/cypermethrin, but not the propetamphos/eucalyptus oil formulation, gave complete resolution of all 4-day-old strikes. Dicyclanil spray-on and ivermectin capsule formulations, both registered for use in sheep, but not for cattle or other livestock species, gave much longer protection against screwworm implants than the currently recommended SC ivermectin. Pre-emptive action to facilitate rapid deployment of these formulations in the event of a screwworm incursion is urgently needed.

Environmental and phylogeographical determinants of the distribution of the Old World screwworm fly in Indonesia

The Old World screwworm (OWS) fly, Chrysomya bezziana, is an obligate parasite of livestock, and the myiasis caused by its larval infestations is economically important in Indonesia. The current spatial distribution of such a pest depends on two main factors: the current environmental conditions in which it can survive; and, its ability to occupy those environments by dispersal, which can be inferred from phylogeography and population genetics. These indicate that all OWS flies in Indonesia have mitochondrial cytochrome b (cyt b) haplotypes of the Asian lineage, and the regional separation of its four sub-lineages is the result of infrequent long-distance dispersal. We report the first investigation to associate regional cyt b sub-lineages of the OWS fly with environmental variables. Principal Components Analysis was used to demonstrate that these sub-lineages are associated with very similar macro-climates throughout Indonesia. Then, a species distribution model for the OWS fly in Indonesia was obtained by using the Maxent program. This indicated that elevation captured information not given by other environmental variables, and cattle density provided the most useful information by itself. The results of our study provide some important leads for future research, which will require better, stratified sampling.

Use of wing morphometrics to identify populations of the Old World screwworm fly, Chrysomya bezziana (Diptera: Calliphoridae): A preliminary study of the utility of museum specimens

The Old World screwworm (OWS) fly, Chrysomya bezziana (Diptera: Calliphoridae), is a major economic and welfare problem for humans and animals in the Old World tropics. Using a bootstrapped log likelihood ratio test of the output of Procrustes principal components and canonical variates analyses for a small sample of museum specimens from which 19 2D wing landmarks had been collected: (1) a consistent and statistically significant difference exists between landmark configurations derived from wings of pinned specimens and those removed from the body and mounted on slides; (2) a highly statistically significant sexual dimorphism in wing morphometry was identified; and (3) a highly statistically significant difference in wing morphometry between populations of the OWS fly from Africa (Tanzania, South Africa Sudan, Zaire, Zimbabwe,) and Asia (Sumba, Indonesia) exists. These results show that wing orientation and gender must be considered when conducting morphometric investigations of OWS fly wings. The latter result is also consistent with results from previous molecular and morphological studies, which indicate there are two distinct genetic lineages within this species. Wing morphometry holds great promise as a practical tool to aid in identification of the geographical origin of introductions of this important pest species, by providing diagnostic markers to distinguish geographical populations and complement molecular diagnostics.

Relative performance of surveys for the Old World screwworm fly, Chrysomya bezziana, in Iraq based on fly trapping and myiasis monitoring

Fly traps are being used to monitor populations of Old World screwworm (OWS) flies in Iraq. We evaluated trapping systems for seasonality and trap type and compared the results with monitoring of OWS flies using myiases on animals. Fly catches increased during spring and autumn with low catches during the hot, dry summer and the cold winter. The effectiveness of the sticky trap/Swormlure and LuciTrap/Bezzilure for OWS flies could not be determined because no OWS were caught during the comparison period in 2009. The LuciTrap caught more flies of all other species than the sticky trap during this comparison. The numbers of myiases detected on animals in Iraqi provinces from 1996 to 2013 are provided. The high numbers of myiases in most provinces in the late 1990s were followed by lower numbers and subsequent apparent elimination in about half of the provinces. Myiases were detected mainly in sheep (77.0%) and goats (16.7%). A temporal comparison of OWS fly detection with traps and animal myiases in Babil province demonstrated a similar sensitivity and a weak correlation between the two methods. We recommend that both fly trapping and inspection of animals for myiases are used for the detection or monitoring OWS fly populations and that Iraq and the international organisations initiate an area-wide integrated OWS fly program, including the sterile insect technique, with the aim of eradicating the OWS fly from Iraq.

An improved real-time PCR assay for the detection of Old World screwworm flies

The Old World screwworm (OWS) fly, Chrysomya bezziana, is a serious pest of livestock, wildlife and humans in tropical Africa, parts of the Middle East, the Indian subcontinent, south-east Asia and Papua New Guinea. Although to date Australia remains free of OWS flies, an incursion would have serious economic and animal welfare implications. For these reasons Australia has an OWS fly preparedness plan including OWS fly surveillance with fly traps. The recent development of an improved OWS fly trap and synthetic attractant and a specific and sensitive real-time PCR molecular assay for the detection of OWS flies in trap catches has improved Australia's OWS fly surveillance capabilities. Because all Australian trap samples gave negative results in the PCR assay, it was deemed necessary to include a positive control mechanism to ensure that fly DNA was being successfully extracted and amplified and to guard against false negative results. A new non-competitive internal amplification control (IAC) has been developed that can be used in conjunction with the OWS fly PCR assay in a multiplexed single-tube reaction. The multiplexed assay provides an indicator of the performance of DNA extraction and amplification without greatly increasing labour or reagent costs. The fly IAC targets a region of the ribosomal 16S mitochondrial DNA which is conserved across at least six genera of commonly trapped flies. Compared to the OWS fly assay alone, the multiplexed OWS fly and fly IAC assay displayed no loss in sensitivity or specificity for OWS fly detection. The multiplexed OWS fly and fly IAC assay provides greater confidence for trap catch samples returning negative OWS fly results.

Genetic diversity of populations of Old World screwworm fly, Chrysomya bezziana, causing traumatic myiasis of livestock in the Gulf region and implications for control by sterile insect technique

Fly larvae were collected from 181 cases of traumatic myiasis in livestock in 10 regions of four countries in the Middle East Gulf region: Iran, Iraq, Saudi Arabia and Oman. The predominant fly species responsible for cases was the Old World screwworm (OWS) fly, Chrysomya bezziana Villeneuve (Diptera: Calliphoridae). In cases from Iran and Oman, which included non-OWS fly species, OWS fly was found solely responsible for 67.6% of cases and jointly with other fly species for a further 12.7% of cases. The major hosts were sheep and goats, together comprising 84.6% of the total, which reflects their predominance among the livestock of these Gulf countries. The major site of wounding on sheep and goats was the tail (40.3%), followed by female genitalia (14.0%). The 3' terminal 715 nucleotides of the mitochondrial cytochrome b gene were sequenced for 178 larvae of OWS. Five haplotypes were identified: three had been recorded previously in the region (two were common throughout and one was unique to Oman), and two were newly identified, one from southern Iraq and the other from Saudi Arabia, both in regions sampled for the first time. The haplotypes varied from one another only at one or two nucleotide sites, equivalent to an intraspecific difference of 0.14-0.28% across the entire 715-bp fragment. There was a single statistically significant association between host species and haplotype in Saudi Arabia, a first such record for OWS fly. The small degree of genetic diversity between geographical populations of OWS fly within the Gulf region suggests that a single Gulf colony could be used to implement the sterile insect technique within an integrated control programme.