Effects of combinations of the essential oils trans-anethole, thymol and carvacrol against larvae of the screwworm fly Cochliomyia hominivorax in vitro

This study investigated the combined effect of trans-anethole, carvacrol and thymol on third-instar larvae of C. hominivorax. For this experiment, third-stage larvae of C. hominivorax were removed from a laboratory colony to perform an in vitro bioassay. The three volatile compounds used in this study, trans-anethole, carvacrol and thymol. Different dilutions of these volatile compounds were performed with the diluent acetone (99.5 %) to determine the associative effect (synergism, addition or antagonism). Three concentrations below the estimated LC50 were prepared (10, 20 and 100 μg.cm-2). These compounds were impregnated in filter paper discs, which were dried and transferred to Petri dishes. Ten larvae were added to each dish and incubated in climate-controlled chambers at 28 ± 1 ºC and 75 ± 10 % relative humidity for 24 and 48 hours. Mortality was assessed based on the absence or change in larval movement, as observed under a stereomicroscope. After 24 hours, trans-anethole (A) caused mortality rates in the range of 23-33.5 %, carvacrol (C) of 9-59 % and thymol (T) of 27-81.5 %, in the three concentrations evaluated. The combination of trans-anethole with carvacrol resulted in mortality rates between 11 % and 50 %, demonstrating antagonistic action. The combination of trans-anethole with thymol caused mortality of 12.5-55.5 %, and the combination of carvacrol with thymol generated mortality of 75.5-99.5 %, indicating synergism. After 48 hours, (A) produced a mortality range of 29-49 %, (C) of 10.5-63 %, and (T) of 37.5-86 % in the three concentrations, maintaining the same relationship of antagonistic and synergistic activity. The combination of trans-anethole with carvacrol resulted in mortality rates between 16 % and 56.5 %, while the combination of trans-anethole with thymol caused mortality of 27.5-62.5 % and the combination of carvacrol with thymol presented mortality between 83 % and 99.5 %. Hence, there was an antagonistic effect when trans-anethole was associated with carvacrol and thymol and a dose-dependent synergistic effect when carvacrol was associated with thymol against third instar larvae of C. hominivorax.

Homeopathic Pyrogenium Ointment as Adjuvant in Treatment of Traumatic and Infected Myiasis by Cochliomyia Hominivorax (Diptera: Calliphoridae) in Sheep: A Case Series

BACKGROUND

The blowfly Cochliomyia hominivorax (Diptera: Calliphoridae) causes traumatic myiasis in farm animals, with deeply embedded larvae that lead to serious tissue damage and sometimes death. Treating this form of myiasis is difficult, often resulting in poor outcomes. As a homeopathic preparation that can mimic traumatic myiasis symptoms, Pyrogenium could potentially supplement treatment. This study aimed to describe the adjuvant effect that a Pyrogenium ointment might have in the treatment of sheep with traumatic myiasis.

PATIENTS

The study reports a homeopathic adjuvant treatment with Pyrogenium 12cH ointment in six sheep with traumatic and infected myiasis. Daily clinical examinations were performed to monitor the evolution of the health of animals. Pyrogenium 12cH ointment was applied topically on the wounds, after cleaning and mechanical removal of the larvae from the lesion. Blood samples were collected for blood counts, and wound exudate samples were obtained for bacteriological examination before and after wound treatment.

RESULTS

The ointment of Pyrogenium 12cH limited the development of parasitic larvae and was associated with the repair of tissue losses resulting from the myiases and with subsequent wound healing, together with control of fever and local inflammation.

CONCLUSION

Homeopathic Pyrogenium 12cH, formulated as an ointment, may be a useful new and adjuvant therapeutic option for treating traumatic and infected myiasis in animals.

Homeopathic Sulphur Ointment as Adjuvant in the Treatment of Sheep with Myiasis by Cochliomyia hominivorax (Diptera: Calliphoridae): A Case Series

BACKGROUND

Myiasis by Cochliomyia hominivorax (Diptera: Calliphoridae) is a serious problem in animal health. Homeopathic Sulphur presents similarity with the clinical presentation verified in these cases and has already shown in vitro efficacy on the blowfly that causes this pathology. This article presents the report of a series of clinical cases of myiasis by C. hominivorax in sheep that underwent adjuvant treatment with homeopathic Sulphur and presents a theoretical-scientific discussion of biological events related to the clinical treatment of the condition.

PATIENTS

Seven naturally occurring myiases affecting sheep from an experimental farm were treated by an ointment impregnated with the homeopathic medicine Sulph 12cH, used as adjuvant after the manual removal of accessible larvae from the wound during wound cleaning. The animals were treated daily and evaluated clinically until complete healing of the lesions. Clinical information on the evolution of the inflammatory and scarring process was collected. Blood counts and bacteriological examinations were performed before and after topical homeopathic treatment.

RESULTS

The homeopathic ointment Sulph 12cH was able to inhibit the development of parasitic C. hominivorax larvae and promote tissue repair and healing in naturally occurring myiasis in the sheep of this study.

CONCLUSION

The homeopathic medicine Sulphur, formulated as an ointment, may be a useful new and adjuvant therapeutic option for treating myiasis in animals.

Does tail docking prevent Cochliomyia hominivorax myiasis in sheep? A six-year retrospective cohort study

Tail docking is a husbandry practice widely incorporated in sheep farms around the world. It is an irreversible mutilation that impairs animal welfare, both immediately and in the longer term. The defence of tail docking as a practice is centred around the perception that doing so contributes to the promotion of local hygiene, allowing the use of the wool, facilitating reproductive management and reducing the chances of myiasis, a disease caused by the invasion of blowfly larvae in the tissues of warm-blooded animals. However, current understanding of farm animal welfare questions the need to maintain practices such as tail docking. Thus, the aim of this study was to evaluate the effect of tail docking on the incidence of Cochliomyia hominivorax myiasis in sheep in an experimental flock in Brazil during a six-year retrospective cohort study. Relative risk, odds ratio and incidence rate ratio were the association measures adopted. A total of 4,318 data-points were collected and supplied the analytical model. Tail docking did not decrease the risk and, on the contrary, was found to increase the chances of sheep being affected by myiasis. The results support the hypothesis that tail docking is not a protective factor against the occurrence of myiasis and further fuel calls for a rethink of tail docking being deployed as a blanket measure in the prevention of myiasis in sheep.

A chromosomal-scale reference genome of the New World Screwworm, Cochliomyia hominivorax

The New World Screwworm, Cochliomyia hominivorax (Calliphoridae), is the most important myiasis-causing species in America. Screwworm myiasis is a zoonosis that can cause severe lesions in livestock, domesticated and wild animals, and occasionally in people. Beyond the sanitary problems associated with this species, these infestations negatively impact economic sectors, such as the cattle industry. Here, we present a chromosome-scale assembly of C. hominivorax's genome, organized in 6 chromosome-length and 515 unplaced scaffolds spanning 534 Mb. There was a clear correspondence between the D. melanogaster linkage groups A-E and the chromosomal-scale scaffolds. Chromosome quotient (CQ) analysis identified a single scaffold from the X chromosome that contains most of the orthologs of genes that are on the D. melanogaster fourth chromosome (linkage group F or dot chromosome). CQ analysis also identified potential X and Y unplaced scaffolds and genes. Y-linkage for selected regions was confirmed by PCR with male and female DNA. Some of the long chromosome-scale scaffolds include Y-linked sequences, suggesting misassembly of these regions. These resources will provide a basis for future studies aiming at understanding the biology and evolution of this devastating obligate parasite.

Effect of Ointments of Sulphur or Pyrogenium on Larvae of Cochliomyia hominivorax (Diptera: Calliphoridae)

BACKGROUND

 Myiasis by Cochliomyia hominivorax (Diptera: Calliphoridae) is a serious problem in animal health in tropical and sub-tropical regions. Ointment-type preparations are a good option of formulation in cases of myiasis in farm and pet animals. Sulphur and Pyrogenium have already shown in-vitro efficacy on C. hominivorax. This article describes an in-vitro experiment to test the inhibition of development from exposing larvae of C. hominivorax to two homeopathic ointments (prepared individually with Sulphur or Pyrogenium).

METHODS

 The homeopathic ointments were produced by mixing sterile lanolin, tocopherol and homeopathic medicine on a hydroalcoholic basis according to the Brazilian Homeopathic Pharmacopoeia. Larvae were obtained from naturally occurring myiases in sheep (wild larvae) or from a laboratory colony. The test consisted of exposing a group of 10 third-stage C. hominivorax wild larvae in contact with Sulphur or Pyrogenium ointment, or a group of 15 laboratory-propagated larvae in contact with the alcoholic vehicle of the ointment or homeopathic medicines prepared in sterile water (Sulphur or Pyrogenium), and observing the effect on the development, longevity and fertility of the blow-fly specimens.

RESULTS

 The C. hominivorax larval inhibition rate was 90.0% for the Sulphur ointment group and was 86.0% for the Pyrogenium ointment group. The non-alcoholic vehicle and the alcoholic vehicle inhibited the development of 24.0% and 22.08% of the larvae respectively. Sulphur prepared in sterile water inhibited the development of 74.67% and Pyrogenium in sterile water inhibited 73.33% of larvae. Specimens that survived contact with homeopathic ointments had their longevity decreased and did not reproduce.

CONCLUSION

 Ointments of Sulphur or Pyrogenium were able to inhibit the development of C. hominivorax larvae. The ointment vehicle was harmless.

Efficacy of afoxolaner (NexGard®) on the treatment of myiasis caused by the New World screwworm fly Cochliomyia hominivorax (Diptera: Calliphoridae) in naturally infested dogs

New World screwworm (NWS) myiasis is an infestation by Cochliomyia hominivorax larvae that consume the living tissue of warm-blooded animals, including humans. Domestic dogs are among the potential hosts of these flies that lay their eggs on the edges of wounds. NWS myiasis cases can be fatal if untreated. Treatment with parasiticides must be fast-acting, long-lasting and show 100% efficacy, since open wounds can be reinfested. Afoxolaner is a molecule from the isoxazoline family with proven ectoparasiticide action against fleas, ticks and mites in dogs. Fourteen healthy client-owned dogs, naturally infested by C. hominivorax larvae, were treated with afoxolaner (NexGard®) as per label recommendations, providing at least the minimum dosage of 2.5 mg/kg. Maggot infestations were classified as light (fewer than 10 larvae), mild (from 10 to 20 larvae) or severe (more than 20 larvae), according to the number of larvae found in the wound and/or collected from the ground after treatment. Twenty-four hours post-treatment, infested lesions were carefully inspected and collected larvae were counted and classified as live or dead. All maggots were identified as second and third instar larvae of C. hominivorax and were found dead within 24 h after treatment, demonstrating 100% larvicidal efficacy against C. hominivorax.

New World screwworm (Cochliomyia hominivorax) myiasis in feral swine of Uruguay: One Health and transboundary disease implications

Background

Feral swine (Sus scrofa) are highly invasive and threaten animal and human health in the Americas. The screwworm (Cochliomyia hominivorax) is listed by the World Organization for Animal Health as a notifiable infestation because myiasis cases affect livestock, wildlife, and humans in endemic areas, and outbreaks can have major socioeconomic consequences in regions where the screwworm has been eradicated. However, a knowledge gap exists on screwworm infestation of feral swine in South America, where the screwworm is endemic. Here, we report screwworm infestation of feral swine harvested in Artigas Department (Uruguay), where the Republic of Uruguay shares borders with Brazil and Argentina.

Methods

Myiasis caused by the larvae of screwworm were identified in feral swine with the support and collaboration of members of a local feral swine hunting club over a 3-year period in the Department of Artigas. Harvested feral swine were examined for the presence of lesions where maggots causing the myiasis could be sampled and processed for taxonomic identification. The sites of myiasis on the body of infested feral swine and geospatial data for each case were recorded. The sex and relative size of each feral swine were also recorded. Temperature and precipitation profiles for the region were obtained from public sources.

Results

Myiases caused by screwworms were recorded in 27 of 618 the feral swine harvested. Cases detected in males weighing > 40 kg were associated with wounds that, due to their location, were likely caused by aggressive dominance behavior between adult males. The overall prevalence of screwworm infestation in the harvested feral swine was associated with ambient temperature, but not precipitation. Case numbers peaked in the warmer spring and summer months.

Conclusions

This is the first report on myiasis in feral swine caused by screwworm in South America. In contrast to myiasis in cattle, which can reach deep into host tissues, screwworms in feral swine tended to cause superficial infestation. The presence of feral swine in screwworm endemic areas represents a challenge to screwworm management in those areas. Screwworm populations maintained by feral swine may contribute to human cases in rural areas of Uruguay, which highlights the importance of the One Health approach to the study of this invasive host species–ectoparasite interaction.