Parasites are ubiquitous across species, and their co-evolution with their chosen host is a remarkable feature of some very complex, intertwined relationships (Wilson and Cotter, 2013). Even us human beings harbour parasites, such as the microscopic lice, Demodex folliculorum, which are found on our eyelashes (Rather and Hassan, 2014)! These mites eat sebum and other by-products of skin and hair metabolism. In a similar way, bird feather mites (superfamilies Analgoidea and Pterolichoidea) may have a role in “feather cleaning” by consuming detritus, such as fungal and bacterial growth and used preen oil, from across a bird’s plumage (Doña et al., 2019). Parasites depend on their host for survival and if they cause excessive damage to the host that impedes its chances of survival then the parasite itself is doomed.
The close evolutionary relationship between the parasite and the host can make parasite treatment difficult and therefore knowledge of the parasite’s lifecycle and when it is most susceptible to treatment is required
Healthy animals can cope with a minor parasite load and will employ a range of behavioural and/or physiological means to remove them or to prevent a small number of such freeloaders from becoming a real health challenge. In captive or domestic situations, higher stocking densities of animals and enforced congregation around a limited number of valuable resources (eg feeding and watering sites or resting areas) increase the likelihood of parasite transmission and higher overall burdens. Stress, due to inappropriate social group, lack of space and poor diet, can also predispose captive or companion animals to unmanageable parasite loads due to a weakened immune response (Beldomenico and Begon, 2015). The close evolutionary relationship between the parasite and the host can make parasite treatment difficult and therefore knowledge of the parasite’s lifecycle and when it is most susceptible to treatment is required (Wells and Flynn, 2022).
Knowing when an avian ectoparasite (those that live and reproduce externally to the host’s body, eg in the bird’s plumage or on its legs or skin) or endoparasite (those that live and reproduce within the host’s body, eg in the bird’s gastrointestinal system) is most susceptible to eradication can help bird owners plan their anti-parasite treatment procedures. This could be targeting an intermediate host (a host that the parasite transiently occupies while it matures into a breeding adult stage) and removing this part of the life cycle, or using treatment when a parasite is moulting into a new skin or developing from a juvenile into an adult form, as this is when antiparasitic drugs are more likely to have an effect.
For owners of companion bird species (eg budgerigars, cockatiels, canaries and zebra finches) or domestic fowl and poultry (hens, ducks, geese and turkey), to more exotic species of captive bird (peafowl and ornamental waterfowl), it is essential to understand the link between good care and parasite control. Like most diseases, prevention is better than cure. Allowing birds room to preen and bathe, so that plumage is kept in good condition, manually removes feather parasites before they can proliferate. Providing sunbathing opportunities also helps with feather condition (Potter and Hauser, 1974) and dustbathing allows for ectoparasite removal (Martin and Mullens, 2012); owners should be encouraged to change the environment of their birds to give access to such biologically relevant resources that promote bird health and overall good plumage condition.
What are the key avian parasites?
Examples of parasites that bird keepers should remain vigilant for include the following.
Air sac mites (Sternostoma tracheacolum) are especially problematic in species such as Gouldian finches, Erythrura gouldiae (Tidemann et al., 1992).
Scaly-leg mites (Knemidocoptes mutans) are commonly a problem in older poultry. The mite burrows under the scales of the bird’s legs causing crusting and release of exudate as well as inflammation and disfigurement.
As both feather and skin mites can be carried by wild birds segregation of pet/captive birds from free-living birds is an important aspect of parasite control
Scaly-face mites (K. pilae) are found on featherless areas around the eyes, nostrils, cere and bill of the bird. These mites can also be found around the cloaca (vent) and sometimes on the bird’s legs. Mites cause disfigurement of the bill and cere, as well as damage around and to the bird’s eyes, and raised scales on the legs. As both feather and skin mites can be carried by wild birds (Bianco et al., 2022), segregation of pet/captive birds from free-living birds is an important aspect of parasite control.
Feather lice (suborders Ischnocera and Amblycera) in large numbers can cause itching and irritation and poor feather condition. However, the co-evolution of birds and their feather lice means that birds can regulate their population of feather lice via preening and therefore these parasites can be benign (Clayton et al., 2008).
Nematode endoparasites such as gapeworm, Syngamus trachea (which are common in outdoor waterfowl and poultry), ascarids (common in budgies and cockatiels) and Capillaria (tiny thread worms found in many companion parrot and passerine species) should be screened for according to their presence in a bird’s faeces or via behaviour change (eg characteristic gasping for breath and shaking of the head associated with gapeworm).
Protozoan parasites are microscopic pathogens that can be of zoonotic risk to human carers. Examples in cage and companion birds include Giardia (which live in the bird’s intestines), trichomoniasis (caused by Trichomonas gallinae; commonly termed canker) and Plasmodium spp. that are spread by mosquitoes (Hoppes, 2021).
Species sharing the same space and housing, or the same tools that move between enclosures, can spread parasites between different hosts. This is especially true if these parasites live away from the host, only visiting or attaching to the host when they require a meal. One such example is poultry red mites (Dermanyssus gallinae), which easily move between different species of bird and have been recorded on more than 40 different families of bird (Roy et al., 2009). Red mites are particularly problematic to treat because of the large amount of time they spend off the host, hiding in tiny crevices and using thigmokinesis (movement in response to touch) and pheromones to aggregate into larger clusters (Sparagano et al., 2014). Red mites only make contact with a host when they need a blood meal, therefore on-host treatments may not be effective. Disinfection and cleaning of bird housing is the recommended course of action, removing as many mite hiding places as possible and using sticky traps inside nest boxes or other covered indoor areas to check for the burden of mites in housing (Figure 1). As some species of mites can be vectors for the transmission of bacterial or viral disease, and can also have zoonotic potential, being watchful for their presence is good practice.
Top tips for parasite control
The best ways for a pet bird owner to reduce (as far as possible) the chances of any form of parasite from becoming a problem and infecting their birds are to:
- Wash hands before and after handling birds and their environment (eg cages, furnishings)
- Clean clothing and shoes after any contact with other birds
- Check the general environment of the cage or enclosure daily to ensure highest level of cleanliness
- Provide fresh food and water each day to reduce chances of spillage and contamination
- Provide the correct type of food for the bird species being kept ensuring that each species remains in good condition and can mount a strong immune response against potential pathogens
- Reduce unwanted stress, protect from wild birds (to reduce contamination) and ensure that social structure is appropriate for a species
- Avoid any bathing water becoming a reservoir for disease or vectors of parasites
- Clean and disinfect housing, perching, aviary panel and cages frequently
- Quarantine new avian arrivals to the existing bird collection
- Seek veterinary attention when birds show any sign of poor health
- Isolate or remove sick birds from the main flock if they show signs of disease. This also makes it easier to collect samples (eg faecal samples) for parasite testing
- Ensure that the general environment around the birds (and where tools used for bird care are housed) is an unattractive one for parasites and their intermediate hosts to live in (ie by keeping such areas clean, tidy, well maintained and hygienic)
- Avoid keeping birds on over-used, “stale” ground that may have been contaminated by other birds previously