Avian Parasites: Mites, Lice, and Internal Parasites Including Gapeworm

Avian parasitism encompasses a diverse array of ectoparasites and endoparasites that compromise host health, productivity, and food safety. This article provides a systematic review of the major arthropod and helminth parasites of birds with emphasis on poultry, covering etiology, epidemiology, clinical signs, pathology, diagnostics, treatment, and control. The discussion integrates recent molecular and ecological findings and addresses the implications of parasitism for egg and meat production.

Ectoparasites: Mites and Lice

Respiratory and Integumentary Mites

Mites (subclass Acari) are among the most economically significant ectoparasites of poultry. The poultry red mite Dermanyssus gallinae and the northern fowl mite Ornithonyssus sylviarum are obligate haematophagous parasites that cause anemia, dermatitis, and reduced egg production. D. gallinae is primarily nocturnal and hides in crevices during the day, whereas O. sylviarum remains on the host. Heavy infestations can lead to death in young birds [1].

The respiratory mite Sternostoma tracheacolum infests the trachea and air sacs of passerines and galliforms, causing dyspnea and open-mouthed breathing. A study by Burke et al. [1] demonstrated that doramectin administration significantly reduced respiratory mite-associated mortality in a population of Gouldian finches (Chloebia gouldiae). The avermectin class drugs act by potentiating glutamate-gated chloride channels in arthropod nerve and muscle cells, leading to paralysis and death of the mite [1].

Feather mites and quill mites cause damage to plumage and skin. Skoracki et al. [2] reported new host records for quill mites (family Syringophilidae) parasitising African shrikes, revealing host and habitat specificity. These mites feed on soft tissue within the feather shaft (calamus) and can impair thermoregulation and flight [2].

The distribution of the fecund mite Megninia ginglymura in poultry is influenced by rearing system and oviposition microhabitat. Galvão et al. [3] found that hens kept in semi-arid regions with free-range systems had higher mite burdens due to greater availability of dust and organic debris for oviposition, compared to confined birds in humid regions [3].

Lice (Phthiraptera)

Avian lice are obligate, host-specific ectoparasites that feed on feather barbules, skin debris, or blood. The major genera affecting poultry include Menopon, Menacanthus, Goniocotes, and Lipeurus. Lice cause irritation, feather loss, and decreased growth rates. Heavy infestations can result in reduced feed conversion and egg production.

Diagnosis of lice is based on visual inspection of feathers and skin for adult lice and nits (eggs attached to feather shafts). Treatment involves the application of permethrin-based powders or sprays. Ivermectin administered via drinking water is also effective. The life cycle of lice is completed entirely on the host; eggs hatch in 4–7 days, and nymphs reach adulthood in 2–3 weeks.

Ticks and Hippoboscid Flies

Ticks (Ixodidae) are occasional parasites of birds. Tan et al. [4] reported Haemaphysalis wellingtoni from the spotted wood owl (Strix seloputo), a new tick-host record in Peninsular Malaysia. Pitó et al. [5] reviewed hard tick infestations of birds of prey across the Western Palearctic, noting that ticks can transmit Borrelia, Babesia, and other pathogens.

The hippoboscid fly Ornithomya avicularia is a blood-feeding ectoparasite of birds. Triseleva et al. [6] investigated morphological and genetic variation in O. avicularia populations across northeastern Eurasia, revealing cryptic diversity that may influence vector competence [6].

Internal Parasites

Protozoan Parasites: Trichomonas gallinae

Trichomonas gallinae is a flagellated protozoan that causes avian trichomonosis, primarily in columbiforms but also in raptors and passerines. The parasite inhabits the upper digestive tract, causing caseous lesions in the oropharynx, esophagus, and crop. Hajiannejad et al. [7] reported a prevalence of 27.3% in pigeons in the Mashhad area of Iran and identified three genotypes (A, B, and C) by PCR targeting the ITS1-5.8S-ITS2 region [7]. Garreta-Celemín et al. [8] found the parasite in European turtle doves (Streptopelia turtur) along their western migratory route, with higher prevalence in birds using supplementary feeding sites. Pereira et al. [9] detected T. gallinae in captive synanthropic birds in southeastern Brazil and reported a novel genotype, underscoring the genetic diversity and potential for cross-species transmission [9].

Cestodes and Other Helminths

Cestodes (tapeworms) are common intestinal parasites of birds, transmitted by intermediate hosts such as beetles, ants, or earthworms. Elmaleck [10] conducted a parasitological survey of urban pigeons in the New Valley, Egypt, and found a high prevalence of cestodes (61.1%) and the protozoan Haemoproteus columbae. Cestode infections reduce nutrient absorption and may cause intestinal obstruction in heavy burdens [10].

Gapeworm (Syngamus trachea)

Gapeworm is a nematode of the genus Syngamus, most commonly Syngamus trachea, that infects the trachea of galliform birds, leading to the characteristic symptom of open-mouthed breathing (gaping). Adult worms are red, about 0.5–2 cm in length, and permanently copulated (forming a Y-shape in the trachea). The life cycle is direct or indirect via paratenic hosts such as earthworms. After ingestion of infective eggs or larvae, third-stage larvae penetrate the intestinal wall and migrate via the bloodstream to the lungs and trachea. Pathogenesis includes mechanical obstruction, inflammation, and secondary bacterial pneumonia. Diagnosis is based on clinical signs, necropsy, and detection of double-operculated eggs in feces or oral swabs. Treatment includes benzimidazoles (fenbendazole) or levamisole [1]. The article Syngamus trachea (Gapeworm) Infection in Chickens: Diagnosis and Treatment provides further detail.

Other Nematodes and Trematodes

Ascaridia galli and Heterakis gallinarum are large roundworms of the small intestine and ceca, respectively. H. gallinarum is the vector of Histomonas meleagridis in turkeys. Capillaria species infect the crop, small intestine, and ceca. Trematodes such as Pegosomum bubulcum are bile duct flukes of waterbirds. Oh et al. [11] reported ectopic parasitism of P. bubulcum in the liver parenchyma of an Eastern great egret, indicating aberrant migration [11]. Davitkov et al. [12] provided the first report of the spirurid nematode Synhimantus laticeps in a long-eared owl in Serbia, recovered from the proventriculus [12].

Chicken Parasites in Eggs

Parasites can affect egg quality and safety. Dermanyssus gallinae infestations cause redness and spotting on eggshells due to crushed mites. Internal parasites such as Ascaridia galli larvae may occasionally be found inside eggs when female worms migrate into the oviduct. Nematode eggs (e.g., Capillaria spp.) can contaminate the egg surface via fecal contact. Egg contents are rarely contaminated with parasites, but food safety concerns exist. The article Parasites in Poultry Eggs: Risks and Prevention discusses this further.

Chicken Parasites in Meat

Parasite transmission through poultry meat is primarily a concern with protozoa such as Toxoplasma gondii (not host-specific to birds but can be carried by chickens) and Sarcocystis spp. Nematodes like Ascaridia and Capillaria are not considered zoonotic, but their presence in muscle (e.g., Dermanyssus mites trapped under skin) can lead to carcass condemnation. The article Parasites in Chicken Meat: Food Safety and Human Health provides a detailed review.

Diagnostic Approaches

Diagnosis of avian parasites involves multiple modalities:

1. Clinical examination: Observation of gaping (gapeworm), feather loss (lice/mites), anemia (mites), and nasal discharge (respiratory mites).
2. Fecal examination: Flotation and sedimentation for nematode, cestode, and trematode eggs. Gapeworm eggs are double-operculated, about 80–100 µm × 45–60 µm.
3. Direct microscopy: Scrapings from trachea (gapeworm), skin scrapings (mites), and wet mounts from oropharynx (Trichomonas).
4. PCR and genotyping: For species identification and strain typing, especially for Trichomonas gallinae [7, 9] and Syngamus [1].
5. Necropsy: Recovery of adult helminths and visualisation of lesions.

The following Mermaid diagram summarises the diagnostic decision tree for respiratory parasites in poultry:

flowchart TD
    A[Bird with dyspnea, gaping, coughing], > B{Nasal/ocular discharge?}
    B, Yes, > C[Consider respiratory mites or mycoplasma]
    B, No, > D[Fecal flotation and tracheal swab]
    D, > E{Double-operculated eggs?}
    E, Yes, > F[Gapeworm - treat with fenbendazole]
    E, No, > G{Mite observed on swab?}
    G, Yes, > H[Sternostoma or tracheal mites - treat with doramectin]
    G, No, > I[Consider bacterial or viral etiology]

Treatment and Control

Therapeutic approaches must be integrated with biosecurity measures.

Antiparasitic Agents

• Macrocyclic lactones: Doramectin has shown efficacy against respiratory mites [1]. Ivermectin is used for lice and D. gallinae.
• Benzimidazoles: Fenbendazole and flubendazole effective against Syngamus trachea, Ascaridia galli, and Capillaria.
• Nitroimidazoles: Metronidazole used for Trichomonas gallinae [7].
• Pyrethrins: Permethrin dusts for lice and mites.

Control Measures

• Housing: Regular cleaning, disinfection, and removal of organic debris to reduce mite refugia [3].
• Quarantine: New birds should be isolated and treated.
• Pasture rotation: For free-range systems, rotating ranges reduces egg and larval contamination.
• Biological control: Predatory mites (Cheyletus spp.) can reduce D. gallinae populations in litter.

Pathological and Economic Impacts

Parasite burdens are often underestimated. D. gallinae infestations can reduce egg production by up to 15% and cause mortality in chicks. Gapeworm heavy infections lead to asphyxiation in young birds. Cestode infections impair weight gain in broilers. In breeder flocks, tapeworm infestations reduce hatchability. The presence of visible parasites in meat or eggs triggers regulatory action and consumer rejection.

Ectoparasites like D. gallinae and O. sylviarum are vectors of bacterial and viral pathogens. M. ginglymura distribution is influenced by rearing system and climate [3]. The control of these parasites requires a holistic approach combining hygiene, parasite monitoring, and rational antiparasitic use.

Conclusion

Avian parasites remain a significant challenge in poultry production. Recent research has elucidated the genetic diversity of Trichomonas gallinae [7, 8, 9], the host specificity of mites [2, 3], and the distribution of ticks on wild birds [4, 5]. The one-health importance of these parasites necessitates continued surveillance, molecular diagnostics, and evidence-based control. The articles Comprehensive Classification of Types of Chicken Parasites and Poultry Parasites in Meat and Eggs provide complementary perspectives.

References

[1] Burke A, Burns R, Fraess G, et al. The Use of Doramectin Reduces Respiratory Mite Associated Mortality in a Population of Gouldian Finches (Chloebia gouldiae). J Avian Med Surg. 2026. URL: https://pubmed.ncbi.nlm.nih.gov/42301998/

[2] Skoracki M, Hromada M, Wamiti W, et al. Quill Mites Parasitising African Shrikes: New Host Records and Distributional Insights Into Host and Habitat Specificity. J Parasitol Res. 2026. URL: https://pubmed.ncbi.nlm.nih.gov/42266599/

[3] Galvão IVC, Duarte MBG, Cáceres JSD, et al. Potential drivers of Megninia ginglymura (Mégnin) distribution in poultry hens: rearing-system and oviposition microhabitat factors across humid and semi-arid regions. Vet Res Commun. 2026. URL: https://pubmed.ncbi.nlm.nih.gov/42234019/

[4] Tan LP, Roslan NS, Kazim AR, et al. Haemaphysalis wellingtoni (Acari: Ixodidae) from the spotted wood owl (Strix seloputo) (Aves: Strigiiformes): a new tick-host record in Peninsular Malaysia. Trop Biomed. 2026. URL: https://pubmed.ncbi.nlm.nih.gov/42126895/

[5] Pitó A, Sándor AD, Horváth M, et al. Hard tick infestation of birds of prey (Aves: Accipitriformes, Strigiformes, Falconiformes) in the Western Palearctic: New data and literature review. Ticks Tick Borne Dis. 2026. URL: https://pubmed.ncbi.nlm.nih.gov/42085891/

[6] Triseleva T, Safonkin A, Matyukhin A, et al. Morphological and genetic variation in the Ornithomya avicularia (Diptera: Hippoboscidae) populations across northeastern Eurasia. Int J Parasitol Parasites Wildl. 2026. URL: https://pubmed.ncbi.nlm.nih.gov/42183171/

[7] Hajiannejad Z, Nourani H, Razmi G. Prevalence and Genotyping of Trichomonas gallinae in Pigeons in the Mashhad Area, Khorasan Razavi Province, Iran. Vet Med Sci. 2026. URL: https://pubmed.ncbi.nlm.nih.gov/42165349/

[8] Garreta-Celemín CL, Cabezón O, Ribas MP, et al. OCCURRENCE OF TRICHOMONAS GALLINAE IN THE EUROPEAN TURTLE DOVE (STREPTOPELIA TURTUR) ALONG ITS WESTERN MIGRATORY ROUTE. J Wildl Dis. 2026. URL: https://pubmed.ncbi.nlm.nih.gov/42082192/

[9] Pereira AG, Simões SRJS, Silva MCCD, et al. Occurrence and Genetic Diversity of Trichomonas gallinae in Captive Synanthropic Birds in Southeastern Brazil. Pathogens. 2026. URL: https://pubmed.ncbi.nlm.nih.gov/42075755/

[10] Elmaleck BSA. Prevalence and impact of cestodes and protozoan Haemoproteus columbae in urban pigeons, first parasitological insights in New Valley, Egypt. Vet Parasitol Reg Stud Reports. 2026. URL: https://pubmed.ncbi.nlm.nih.gov/42034949/ *** Disclaimer: This article is for educational and informational purposes only. It is not intended to substitute for professional veterinary advice, diagnosis, treatment, or regulatory guidance. Always consult a licensed veterinarian or qualified specialist regarding animal health, disease diagnosis, and therapeutic decisions.

[11] Oh B, Park BK, Kim M, et al. Ectopic Parasitism of Pegosomum bubulcum in an Eastern Great Egret (Ardea alba modesta). J Wildl Dis. 2026. URL: https://pubmed.ncbi.nlm.nih.gov/42091121/

[12] Davitkov D, Nićković E, Vučićević M, et al. First report of Synhimantus laticeps in long-eared owl in Serbia. Vet Parasitol Reg Stud Reports. 2026. URL: https://pubmed.ncbi.nlm.nih.gov/42034958/