Abstract

Background

Northern fowl mites (Ornithonyssus sylviarum) are obligate hematophagous ectoparasites of both feral birds and poultry, particularly chicken layers and breeders. They complete their entire life-cycle on infested birds while feeding on blood. Infestations of O. sylviarum are difficult to control and resistance to some chemical classes of acaricides is a growing concern. The contact susceptibility of O. sylviarum to a new active ingredient, fluralaner, was evaluated, as well as other compounds representative of the main chemical classes commonly used to control poultry mite infestations in Europe and the USA.

Methods

Six acaricides (fluralaner, spinosad, phoxim, propoxur, permethrin, deltamethrin) were dissolved and serially diluted in butanol: olive oil (1:1) to obtain test solutions used for impregnation of filter paper packets. A carrier-only control was included. Thirty adult northern fowl mites, freshly collected from untreated host chickens, were inserted into each packet for continuous compound exposure. Mite mortality was assessed after incubation of the test packets for 48 hours at 75 percent relative humidity and a temperature of 22°C.

Results:

Adult mite LC50 /LC99 values were 2.95/8.09ppm for fluralaner, 1587/3123ppm for spinosad, 420/750ppm for phoxim and 86/181ppm for propoxur. Permethrin and deltamethrin LC values could not be calculated due to lack of mortality observed even at 1000 ppm.

Conclusions:

Northern fowl mites were highly sensitive to fluralaner after contact exposure. They were moderately sensitive to phoxim and propoxur, and less sensitive to spinosad. Furthermore, the tested mite population appeared to be resistant to the pyrethroids, permethrin and deltamethrin, despite not being exposed to acaricides for at least 10 years.

by Bradley A. Mullens, Amy C. Murillo, Hartmut Zoller, Anja R. Heckeroth, Faris Jirjis and Annie Flochlay-Sigognault

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Background

Two major ectoparasite species severely affect the poultry industry worldwide: the northern fowl mite, Ornithonyssus sylviarum, and the poultry red mite, Dermanyssus gallinae.^{1 2} Both mite species are obligate hematophagous parasites able to complete their life-cycles within about 1 week under optimal conditions.^{2 3 4} Mite populations can become dense very quickly in commercial poultry facilities reducing hen performance and profitability.^{5 6} They differ mainly in that all stages of O. sylviarum mites live on the host full time, occupying and laying eggs in the fluffy feathers mostly of the vent region (Fig. 1),¹ while D. gallinae lives predominantly off-host, hidden in cracks and crevices, and comes out nocturnally to feed on the birds.² Classical approaches to treat mite infestations mostly include the use of acaricidal sprays applied to the environment or to the host itself.⁶ However, a complicating factor for both mite species is that they can persist without hosts for weeks and perhaps months in the environment.^{7 8} Their very small size makes them a difficult target for spray treatments and subsequent disinfestation of poultry houses between flocks. In addition, these acaricidal sprays must penetrate the feather layer from under the birds (vent region) to treat O. sylviarum on host, which make it difficult to spray birds in enriched cage or cage-free systems.

Fig. 1 Northern fowl mites (Ornithonyssus sylviarum) on the vent region of an infested hen. A representative cluster of feeding mites indicated by an arrow

In North America, O. sylviarum is the most prevalent ectoparasite of commercial laying hen operations.¹ Control efficiency is threatened by serious mite resistance to a shrinking arsenal of acaricidal compound classes,⁹ especially for the synthetic pyrethroids, but also against carbamates and organophosphates. In the USA synthetic on-host control chemicals for O. sylviarum 15 years ago included the carbamate carbaryl, the organophosphate mixture tetrachlorvinphos/dichlorvos, and permethrin. Currently only permethrin is widely allowed for use, tetrachlorvinphos or its mixture with dichlorvos are used in some states, and carbaryl is no longer allowed.¹⁰ Alternatives to traditional acaricides, such as botanical products or inert dusts, have been explored for both O. sylviarum and D. gallinae control, with inconsistent results; botanical products are notoriously variable, while silica dusts can be difficult to deploy effectively.^{2 10 11} Entomopathogenic fungi, especially Beauveria bassiana and Metarhizium anisopliae, have promise for control of D. gallinae and perhaps of O. sylviarum, although results have been mixed.^{12 13 14} It is critical that we explore other options, including new synthetic acaricides.²

Twenty-first century developments of new classes of acaricidal compounds like isoxazolines, have restored optimism that safe and effective pest control could be maintained for crop, premise protection, and animal health. Isoxazolines work by binding to invertebrate GABA and glutamate channels,¹⁵ but act at previously unrecognised sites. This mitigates cross-resistance to other chemotypes, and differing target sites between arthropods and mammals result in selective toxicity and mechanistically based safety.¹⁶ Isoxazolines, including fluralaner, afoxalaner and sarolaner, are under development and are of increasing importance in the control of external parasites in dogs and cats, including mites.^{17 18 19 20} The present study was conducted to determine if fluralaner possesses contact activity against O. sylviarum, and compare this activity with that of other acaricides commonly used against mite infestations of poultry.

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Conclusion

Northern fowl mites were highly susceptible to fluralaner by contact in this study. This mite resides primarily in the fluffy feathers of the vent region of chickens, where protonymphs and adults blood feed. This ectoparasite causes considerable economic damage to egg laying hens, caused by blood-feeding and the subsequent immune responses.⁶ Pesticide sprays are currently the primary method of controlling O. sylviarum. The pesticides must be sprayed from underneath the birds at high pressures to effectively treat the mites living in the vent feathers. As birds are moved into alternative cages with solid floors and other structures, or cage-free environments, this type of treatment will become difficult to execute. Fluralaner has a higher contact activity than other acaricides we tested for O. sylviarum. This activity, together with its expected systemic activity, as demonstrated for it and other isoxazolines against other mite species,^{16, 19}, would make fluralaner a valuable addition to the poultry mite control palette.

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