Poultry red mite, also known as Dermanyssus gallinae, is one of the most significant parasites affecting backyard chickens. In commercial layers, 60 to 85 percent of flocks are known to have suffered or be suffering from infestations (Fiddes et al., 2005) and this is starting to trickle into backyard flocks.
Some owners will be familiar with red mite and the common signs and symptoms to look out for, but not all. And with chickens a popular pet choice for the UK population (Sabanoglu, 2020), we as veterinary surgeons need to be confident with diagnosing and treating red mite to help owners manage the issue.
Spotting red mite
Red mite is a haematophagous ectoparasite of poultry. The mites themselves are typically 0.5 to 1.5mm in size depending on the lifecycle stage, and are generally either grey or red in colour. They will look red once they have ingested a blood meal.
They commonly reside in cracks and crevices of poultry houses and are most prevalent in warmer conditions. In the UK, infestations are often seen between May and October when temperatures are typically above 10 degrees Celsius, and the red mite lifecycle takes two weeks to complete.
After the eggs are laid, it typically takes up to five days before they take their first feed as protonymphs. When they reach adult stage, at about 10 days old, this is when they will start to feed most frequently.
Adult red mites will take multiple feeds. They tend to feed for an hour at a time every two to three days, laying more eggs in between this. As red mite levels start to build, you can see how this can affect birds through blood loss and irritation.
It’s also worth noting that if temperatures exceed 25 degrees Celsius, the red mite lifecycle can reduce to just seven days, and below nine degrees Celsius, they will become inactive. However, they can still survive for up to eight months without a blood feed meaning once temperatures start to rise, the problem soon starts to rear its head again.
Diagnosing red mite
As well as being very small, red mite are also photophobic meaning they are usually only visible at night. Because the mites are rarely found on the birds during the daytime, this makes it incredibly difficult for owners to physically see the parasites and therefore spot they have a problem.
Finding mites in the environment is a good way to diagnose the issue. Therefore, I often advise owners to place a white sheet on the floor of the coop, when birds go in to roost at night, and wait for at least an hour after dark before shining a torch on the sheet. If red mite are present, they will be crawling across the sheet and visible to the eye.
Red mite will also leave behind a tell-tale ash-like excretion that looks similar to cigarette ash, so suggesting owners look out for this in cracks and crevices of the hen house can help detect the presence of red mite.
It is very unlikely that you will spot red mite on chickens during the day, and therefore if birds are brought into practice you will need to look out for other common clinical signs rather than the physical parasite.
Common clinical signs of red mite
There are a number of common signs that indicate red mite may be an issue in birds. If a number of these clinical signs are present in a flock, then treatment is recommended.
Restless and irritated birds
Red mite can cause irritation, often making birds restless and generally more irritable through the lack of sleep, which can sometimes manifest in aggression towards other chickens. Least dominant birds tend to suffer more from red mite as they often have the less desirable spot in the poultry house due to the natural pecking order. Owners may also find that chickens become more reluctant to roost at night as this is when red mite are most active.
Drop in egg production
Although this may not be a big concern for owners as much as it would be for a commercial laying flock, a drop in egg production and egg quality can be an indication of red mite.
Pale comb and wattle
A comb that is bright red in colour is an indication of a healthy chicken, so if this colour is different from the norm this is a warning sign. Red mite can cause anaemia which the change in comb and wattle colour can be an indication of. If left untreated, this can result in death in severe cases.
Immunosuppression
Red mite can also cause immunosuppression meaning chickens become increasingly susceptible to other pathogens. This is due to the disturbance at night, causing increased levels of corticosterone and adrenalin circulating in the bloodstream, and a decrease in the amount of beta and gamma globulin levels they have in their system (Thomas et al., 2019).
Prevention and treatment
Red mite is notoriously difficult to maintain control over, as once it takes hold it is generally ingrained within the environment. Cleaning and disinfecting chicken coops regularly is often thought to be an effective way of getting on top of red mite, and it is a good idea to remind owners to keep poultry houses well maintained. Plastic houses can be better for controlling red mite as there are fewer cracks and crevices for mite to reside and they can be easier to clean compared to traditional wooden houses.
Isolating new birds for up to five days before introducing them to the existing flock can also be a good way to help minimise the risk of introducing the parasite into a clean flock. However, external factors that are beyond our control mean the likelihood of red mite is inevitable in most cases.
There are various treatment options on the market which can vary in efficacy. For example, environmental sprays capable of killing adult mite are available, but the duration of activity will be variable and it is difficult to ensure the product reaches all areas of poultry houses where red mites are commonly found.
Fluralaner is an active ingredient commonly used in commercial laying units and has recently also become available to pet chicken owners. Trials with the drug have shown that when birds were treated with two doses of the product seven days apart, kill rate of artificial red mite infestation remained between 92.6 and 100 percent 15 days after the first administration (Brauneis et al., 2017), enough to cover two mite lifecycles or potentially more in warmer weather. One of the unique aspects of this treatment is that it focuses on treating the chickens, rather than just the environment, meaning you can target all mites to achieve total control.
