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How significant are parasites of wild birds?

How to diagnose and treat parasites is one of the most common queries I receive as an avian veterinarian. It is not a simple answer and depends on many factors such as the type of parasite, how “nasty” it is to its host and the bird’s own immunity and health. Frequently, wild bird parasites will be found as an “incidental” finding of little clinical significance. Other times parasites will present as a major problem, such as a huge lice or tick burden that has caused a bird to become anaemic and weak.


Parasites are also a common cause of concern for flocks of aviary birds that may have higher numbers of birds in a limited space, where parasite burdens can build up over time.


Globally, there are very common avian parasites such as roundworms, ticks and lice and others that are less commonly seen in birds, such as liver flukes and fleas. Parasites and their significance can also vary by country, region and species of bird.


A seabird has more than 30 lice visible in the feathers of the head
Lice in an Australasian Gannet (Morus serrator). Image: Lynn Miller

Do parasites always harm birds?

No, not always – parasites have often co-evolved with their hosts and many animals live long lives despite the burdens of parasites. There is some evidence that parasites can even help animals, such as by modulating immune responses to reduce inflammation and allergies (Bohnacker et al., 2020). A healthy bird will have natural behaviours to reduce parasite burdens, such as preening and allopreening (preening each other) to physically remove ticks, lice and mites, dust baths may also help with external parasites. Similarly, some internal parasites can be coped with, and the bird’s natural immunity helps to keep many internal parasites in check.

Bird tapeworm measuring 30cm long
A tapeworm found in a post-mortem examination of a Saker Falcon (Falco cherrug). Image: Janelle Ward

I have performed hundreds of post-mortem examinations of birds and so I have personally seen evidence of a full range of effects from parasites. In many cases, parasites did not produce severe reactions in the body when they were in small or moderate numbers. Yet in other cases, birds were so heavily infested that they died from the parasite burdens or complications, such as bowel blockages.



Clusters of tiny red mites gather along the skin between the feathers of a white chicken
Northern Fowl mites in a chicken. Image: Bradley Mullens

We most commonly see significant parasite burdens either in young birds (chicks and juveniles) that have minimal immune or other natural defences or in sick or injured birds that can no longer limit their own infestations. For instance, threatened hihi (stitchbird) chicks were found to have high mortality from mite infestations (Ewen et al.,2009), and debilitated seabirds are often infested with lice.


Parasites, therefore, are a common problem that is seen in birds that come into care for rehabilitation, but the parasites may be secondary to an underlying problem or disease, so it is important to conduct a full health examination even if parasites seem obvious.


How do I treat parasites of birds?

The type of treatment depends on the type and species of parasite. Parasites can be external “ectoparasites” (found on the surface of skin or feathers, or within the skin e.g., feather follicles) or internal “endoparasites” (found within the body organs, gut or other tissue). Examples of ectoparasites include lice, mites and ticks. Examples of internal parasites include whipworms, coccidia and tapeworms. Treatment of external parasites includes manual removal or topical treatments such as mite powders or veterinary products such as fipronil or ivermectin. Beware when using low budget brands as some may not be as effective as others and always seek professional advice on which products are most effective.


Internal parasites frequently occupy the gastrointestinal tract (gut) after being ingested, but lung and air sac parasites are also very common. Some parasites also require to be ingested (eaten) by the host following a life cycle that starts in another (intermediate) host such as a slug, snail, mouse, or other bird. Treatments for internal parasites usually require a tablet or medication for 1-5 days that is either given directly via crop tube or in the feed or drinking water.


However, before we start treating the birds for parasitism we should also ask the question:


Do I need to treat this bird for this parasite?

It is important to realise that some parasites might not be causing harm and the bird will only get reinfected once it is released back to the wild. Also, we need to take care not to cause resistance in parasites by overusing treatments or incorrectly using them. For some parasites, it is important that the host has a small infection to be able to develop natural immunity, such as coccidia.


Knowing your parasites and how to test and monitor them over time are invaluable tools for the care of birds. Diagnostic tests include skin scrapings, feather plucks and physical examination for external parasites, and internal parasites require a faecal egg count, faecal floats, and live wet preparations for some motile protozoa such as Giardia and Trichomonas.


Microscopic view of protozoal parasites on a slide
Trichomonas, cultured. Image: Dr. Josef Reischig, CSc., CC BY-SA 3.0, via Wikimedia Commons

If you would like to know more about the clinical signs (symptoms), identification, diagnosis and treatment of parasites in birds then check out our new online tutorial “Parasites of Birds” which also includes downloadable tables for medications and colour guides to identification, diagnosis and treatment options. Human health & safety, prevention of spread to other birds and management in the aviary environment is also discussed in this affordable course.


Parakeet with feather changes and feather loss due to parasites
Red crowned parakeet / kakariki (Cyanoramphus novaezelandiae) with feather loss due to mite infestation. Image: Janelle Ward
Written by Dr Janelle Ward
Wildlife Veterinarian and Co-Founder of Learn Bird Care Ltd

References

Bohnacker S, Troisi F, de Los Reyes Jiménez M, Esser-von Bieren J. (2020) What Can Parasites Tell Us About the Pathogenesis and Treatment of Asthma and Allergic Diseases. Front Immunol. 2020 Sep 11;11:2106. doi: 10.3389/fimmu.2020.02106


Ewen, J.G., Thorogood, R., Brekke, P., Cassey, P., Karadas, F. & Armstrong, D.P. (2009) Maternally invested carotenoids compensate costly ectoparasitism in the hihi. Proceedings of the National Academy of Sciences of the USA, 106, 12798–12802.


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