The most economically important of the many external parasites of poultry are mites of the families Dermanyssidae and Macronyssidae (poultry red mite, northern fowl mite, and tropical fowl mite) and Trombiculidae (turkey chigger).
The poultry red mite or chicken mite, Dermanyssus gallinae, infests chickens, turkeys, pigeons, canaries, and various wild birds worldwide. These bloodsucking mites will also bite people but cannot survive on or infest them. Although rare in modern commercial cage-layer operations, they are found in cage-free environments such as breeder or small farm flocks. Poultry red mites are nocturnal feeders that hide during the day under manure, on roosts, and in cracks and crevices of the chicken house, where they deposit eggs. Populations develop rapidly during the warmer months and more slowly in cold weather; the life cycle may be completed in only 1 week. A house may remain infested for up to 9 months after birds are removed.
Transmission of the poultry red mite, as well as the northern fowl mite and the tropical fowl mite, is by mite dispersion or by contact with infested birds, animals, or inanimate objects. In the integrated poultry industry, mites are dispersed most frequently on inanimate objects such as egg flats, crates, or coops or by personnel going from house to house or farm to farm.
Heavy infestations of either poultry red mites or northern fowl mites decrease reproductive potential in males, egg production in females, weight gain in young birds, and feed conversion efficiency; they can also cause anemia and death. Poultry red mites may be found in the chicken houses during the day, particularly in nest boxes or in cracks or where roost poles touch supports, or on birds at night. Their role as vectors of other pathogens in nature needs study, but experimental transmission of Eastern, Western, and Venezuelan equine encephalitis viruses, fowl poxvirus, and the bacteria Salmonella Enteritidis, Pasteurella multocida, Coxiella burnetii, and Borrelia anserina has been demonstrated.
Obtaining mite-free birds and using good sanitation practices are important to prevent a buildup of mite populations. Once poultry have been infested, control may be achieved by spraying or dusting the birds and litter or by targeting the inside of the house and all hiding places for poultry red mite (eg, behind nest boxes, cracks and crevices) with a high-pressure sprayer. Inert dusts such as diatomaceous earth and pure synthetic amorphous silicas can be effective, but application rates need to be high when the humidity is very high. Systemic control with ivermectin (1.8–5.4 mg/kg) or moxidectin (8 mg/kg) is effective for short periods, but the high dosages are expensive, close to toxic levels, and require repeated use.
The northern fowl mite, Ornithonyssus sylviarum, is the most important parasite of layers and breeding chickens in the USA and is a serious pest of chickens throughout the temperate zone of other countries. On turkeys, it is second in importance only to the turkey chigger in areas where the turkey chigger is found. It has been reported from many species of birds and from rats, mice, and people; however, fertile populations are reported only on birds. Northern fowl mites are obligate bloodsucking parasites that can complete their life cycle in 5–12 days. Off the host, mites may live up to 4 weeks, depending on temperature and relative humidity. Northern fowl mites are typically found by parting feathers in the vent area, which may have thick, crusty skin, severe scabbing, and soiled feathers. In heavy infestations, they can be found on eggs. Even moderate (>100 mites/bird) infestations can cause decreased egg production and feed conversion efficiency in laying hens.
Prevention of mite introduction to a flock is best because eradication is incredibly difficult. Any acaricidal spray treatments must be applied with sufficient force to penetrate the feathers in the vent area. Resistance to pyrethrins and pyrethroids is widespread, and few other chemical treatments are available for use on birds. Dustboxes with sand and acaricidal materials, such as inert dusts (eg, diatomaceous earth) or sulfur dust, are very effective for bird self-treatment of mites.
Western equine encephalomyelitis, St. Louis encephalitis, and Newcastle disease viruses, as well as fowlpox virus, have been isolated from these mites. However, the mites are not significant vectors of these viruses. Clinical findings and control are similar to those for poultry red mite.
The tropical fowl mite, Ornithonyssus bursa, is distributed throughout the warmer regions of the world and has been reported in Hawaii, Texas, Florida, Illinois, Indiana, Maryland, and New York. It closely resembles the northern fowl mite in its biology and habits but lays a greater proportion of its eggs in the nest. Hosts include chickens, turkeys, ducks, pigeons, sparrows, starlings, mynah birds, and people. Western equine encephalomyelitis virus has been recovered from this mite, but there is no evidence it transmits the virus.
Clinical findings and control are similar to those for poultry red mite.
The scaly leg mite, Knemidocoptes mutans, is a small, spherical, sarcoptic mite that usually tunnels into the tissue under the scales of the legs. It is rare in modern poultry facilities but not uncommon in backyard flocks. When found, it is usually on older birds on which the irritation and exudation cause the legs to become thickened, encrusted, and unsightly. Feet and leg scales become raised, resulting in lameness. Birds stop feeding, and death can result after several months. This mite may occasionally attack the comb and wattles. The entire life cycle is in the skin; transmission is by contact. Infections can be latent for long periods until stress triggers a mite population increase.
For control, affected birds should be culled or isolated, and houses should be cleaned and sprayed frequently, as recommended for the poultry red mite. Individual birds should be treated with oral or topical ivermectin or moxidectin (0.2 mg/kg), 10% sulphur solution, or 0.5% sodium fluoride.
The common chigger, Trombicula alfreddugesi, and other chigger species (harvest mites, red bugs) infest birds and will bite people and other mammals, feeding on partially digested skin cells and lymph. Heavily parasitized birds become droopy, refuse to eat, and may die from starvation and exhaustion. Larvae may be found either singly or in clusters on the ventral portion of the birds. Control on the range is aided by keeping the grass cut short and dusting with acaricides.
The larvae of Neoschongastia americana, the turkey chigger, are parasitic on numerous birds. Across the southern USA, they are the major pest of turkeys ranged on heavy clay soils in the summer. The chiggers feed in groups of as many as 100 mites per lesion for 8–15 days. Turkeys may have 25–30 lesions each. One lesion, 3 mm in diameter, may cause significant downgrading at market time. To prevent downgrading, turkeys must be protected for at least 4 weeks before marketing.
Acaricidal sprays or dusts on turkey ranges control chiggers. A preventive measure now used in many turkey-growing areas includes a shift from range to confinement rearing, or use of sheds to provide shade.
Laminosioptes cysticola, the fowl cyst mite, is a small cosmopolitan parasite of chickens, turkeys, and pigeons that is most often diagnosed by observing white to yellowish caseocalcareous nodules ~1–3 mm in diameter in the subcutis, muscle, lungs, and abdominal viscera. Careful examination of the skin and subcutis of birds under a dissecting microscope frequently reveals the mites. Destroying the bird has been the best control for this parasite, but ivermectin may be effective.
The depluming mite, Neocnemidocoptes gallinae, is found worldwide and burrows into the epidermis at the base of feather shafts, causing intense irritation and feather pulling and loss in chickens, pheasants, pigeons, and geese in spring and summer. Hyperkeratosis, skin lesions, and digit necrosis can result from the burrowing. Affected birds should be isolated and treated with ivermectin or with acaricidal materials.
Most feather mites belong to the families Analgidae, Pterolichidae, and Proctophyllodidae. Surface feather mites feed mainly on feather oils, debris, fungi, and skin scales. More than 25 species, including Megninia cubitalis, M ginglymura, and Pterolichus obtusus, are found on domestic poultry, but they are rare on modern poultry ranches, though there are exceptions. Outbreaks of Allopsoroptoides galli on commercial layer facilities in Brazil have been reported. These infestations caused dermatitis and significant reductions in hen body weights and egg production.
Quill mites (Syringophilidae and Gaudoglyphidae) live in quills and feed on quill tissue or fluids obtained by piercing the calamus wall. Syringophilus bipectinatus is found in chicken and turkey feather quills worldwide, and Columbiphilus polonica, Dermoglyphus elongatus, and Gaudoglyphus minor live in chicken quills in Europe. Feather mites do little economic damage but may reduce egg production via malnutrition, feather loss, and dermatitis. Affected birds should be dusted with acaricides, or oral or topical ivermectin can be applied.