The Condition

Mites are free-living, blood sucking parasites, of which the red mite, Dermanyssus gallinae, and northern fowl mite, Liponyssus (Ornithonyssus) sylvarium, can be a very serious problem. They move quickly over skin and feathers and their blood-sucking activity can cause anaemia when there is a severe infestation. The red mite live off the bird during the daytime, whereas Northern mite live on the bird and thus a different approach to control is required for their control.

The mite feeds mainly at night, remaining in cracks and crevices during daytime, where eggs are laid. As a result, daytime inspection may not detect large populations of red mites. Wild and domesticated flying birds and turkeys are the usual hosts.

The prevalence of mites in organic poultry systems is likely to be higher than in conventional systems (Permin and Nansen, 1996). The red mite is not normally seen in battery systems, but can be a problem in layer houses. A study in Sweden showed that D. gallinae was the only mite present in poultry systems and that 33% of deep litter flocks and 67% of backyard flocks were infested, whilst only 4% of battery systems were affected (Hoglund, Nordenfors, Uggla, 1995). A similar prevalence of 1 in 3 Swedish deep-litter systems was recorded by Ascard, K. Wachenfelt, E. von (1995). In Switzerland, red mites were found in 85% of deep-litter and outdoor systems (Maurer et al, 1993). There was no difference in the abundance of mites between free-range and indoor deep-litter systems or between small and big holdings.

A very serious red mite problem, causing sudden mortality, anaemia and egg drop, was reported on a free-range farm in the south of England by Swarbrick (1986).

The appearance of the red mite can depend on when they last fed; red, black or grey. The life cycle lasts approximately one week and females can then starve for up to 9 months (Kirkwood, 1963). Adult females lay their eggs in poultry houses 12-24 hours after their first blood meal. In warm conditions, these eggs hatch within 48-72 hours. The larvae then moult after 24-48 hours, become blood-sucking nymphs, and then moult again 24-48 hours after this. They develop into adults after a third moult.

Heavy infestation can result in a drop in egg production. Birds may refuse to lay in infested nests.

High and low temperature, relative humidity, and perhaps barometric pressure have effects on the longevity and dispersal of red mites off the host. On the host, mite populations are adversely affected by shortening feather length in the vent area of mature hens. Immature chickens support fewer mites than those that are sexually mature (DeVaney, 1989).

Mites have been known to carry disease organisms, such as those carrying fowl cholera and the fowl spirochete Bolleria anserina.

Microscopic examination of the red mite reveals a V-shaped ventral anal plate compared with the oval plate of the northern fowl mite. Their mouthparts are also different.

Liponyssus (Ornithonyssus) sylvarium, the northern fowl mite, breeds continuously on the host bird and is a particular problem for caged birds. Eggs are normally laid in the cooler regions of the bird. The mite then migrates to the neck. Eggs laid on feathers normally hatch within a day, with larval and nymph stages completed in four days and the entire life cycle within a week.

Inspection can reveal heavy deposits of mite eggs and faeces in the vent area. On inspection of an infected bird, mites will rapidly crawl up the human arm. Parting of the feathers reveals the mite, eggs and excrement. The mites can also be seen crawling on eggs. The northern fowl mite is sometimes confused with the red mite, although, unlike the red mite, it can be found during daytime. Heavy infestations result in blackened feathers and scabby and cracked skin, particularly around the vent, and infested males can be discouraged from breeding.

The problem can increase during the winter, and drop to low numbers in hotter weather. Northern fowl mite can enter poultry flocks by means of new pullets, vehicles and bird crates, or be carried in by people or wild birds.

An acquired immune response of White Leghorn hens to populations of northern fowl mite has been recorded. The degree of acquired immunity was related to the initial level of mite infestation (DeVaney and Ziprin, 1980)

Although the red and northern fowl mite are the most common, Green (1980) found, over a period of years, 10 species of mite in a single poultry house. The depluming itch mite (Cnemidocoptes gallinae) is a burrowing mite that can cause feather loss and stimulate cannibalism. The scaly leg mite, C. mutans, can cause excessively scaly skin and deformed legs. Scaly leg mite lives under the scales of the legs and is normally seen in older hens kept outdoors. Symptoms are irritable lesions covered with white flakes.