Poultry Parasites: Mites, Lice, and Internal Parasites Including Those Transmitted via Eggs
By Dr. Zubair Khalid, DVM, MS, PhD ·
Key Takeaways
- Poultry are susceptible to a broad spectrum of ectoparasites (mites, lice, ticks, fleas) and endoparasites (nematodes, cestodes, trematodes, protozoa), with significant impacts on health, productivity, and food safety.
- Hematophagous mites like Dermanyssus gallinae cause anemia and reduced egg production, while also acting as vectors for bacterial pathogens such as Salmonella.
- Nematodes, particularly Ascaridia galli and Heterakis gallinarum, are prevalent intestinal parasites; H. gallinarum is a critical vector for Histomonas meleagridis, the causative agent of histomonosis.
- Coccidiosis, caused by Eimeria species, is a major protozoan disease characterized by diarrhea and reduced feed conversion, with resistance to anticoccidials being a significant concern.
- Vertical transmission of parasites can occur via eggs, with Capillaria species and Prosthogonimus flukes being examples that can contaminate egg contents or oviducts.
- Diagnostic approaches integrate fecal flotation for helminth eggs and coccidian oocysts, necropsy for direct visualization, and molecular methods like PCR for precise pathogen identification.
Introduction
Poultry production systems are susceptible to a diverse array of parasitic organisms that compromise bird health, welfare, and productivity. These parasites are broadly classified into ectoparasites (mites, lice, ticks, fleas) and endoparasites (nematodes, cestodes, trematodes, protozoa). A subset of these parasites can be transmitted vertically through the egg or horizontally via contaminated meat, posing risks to both flock health and food safety [<a href="#ref-1">1</a>, <a href="#ref-2">2</a>]. This article provides an exhaustive review of the major parasitic groups affecting poultry, with emphasis on their biology, clinical impact, diagnostic approaches, and control strategies.
Ectoparasites: Mites and Lice
Mites
Mites are among the most economically significant ectoparasites of poultry. The poultry red mite, Dermanyssus gallinae, is a hematophagous mite that feeds on blood at night and hides in crevices during the day [<a href="#ref-3">3</a>]. Infestations cause anemia, decreased egg production, and increased mortality. D. gallinae is also a vector for bacterial pathogens such as Erysipelothrix rhusiopathiae and Salmonella species [<a href="#ref-3">3</a>]. The northern fowl mite, Ornithonyssus sylviarum, is a permanent resident on the host, causing severe irritation, feather damage, and reduced feed conversion efficiency [<a href="#ref-4">4</a>]. The scaly leg mite, Knemidocoptes mutans, burrows into the keratin of the legs and feet, causing hyperkeratosis, crusting, and lameness [<a href="#ref-1">1</a>, <a href="#ref-4">4</a>]. Knemidocoptes gallinae (depluming mite) causes feather loss and skin irritation [<a href="#ref-1">1</a>].
Lice
Lice (Mallophaga) are obligate ectoparasites that feed on feathers, skin debris, and blood. Common species include Menacanthus stramineus (body louse), Menopon gallinae (shaft louse), Lipeurus caponis (wing louse), and Columbicola columbae (pigeon louse) [<a href="#ref-1">1</a>, <a href="#ref-2">2</a>]. Lice infestations cause feather damage, reduced growth rates, and decreased egg production. Heavy infestations can lead to anemia and death in young birds [<a href="#ref-4">4</a>]. Lice are host-specific and are transmitted by direct contact or through contaminated fomites.
Ticks and Fleas
The fowl tick, Argas persicus, is a soft tick that feeds on blood and transmits Borrelia anserina (avian spirochetosis) [<a href="#ref-1">1</a>, <a href="#ref-5">5</a>]. Ornithodoros moubata is another soft tick species reported in African poultry systems [<a href="#ref-1">1</a>]. The sticktight flea, Echidnophaga gallinacean, attaches to the skin around the head and eyes, causing irritation and secondary infections [<a href="#ref-1">1</a>].
Internal Parasites: Nematodes, Cestodes, and Trematodes
Nematodes
Nematodes are the most prevalent endoparasites in poultry. Ascaridia galli (large roundworm) resides in the small intestine, causing malnutrition, reduced growth, and decreased egg production [<a href="#ref-6">6</a>, <a href="#ref-7">7</a>]. Heterakis gallinarum (cecal worm) is a common nematode that can carry Histomonas meleagridis, the agent of histomonosis (blackhead) [<a href="#ref-6">6</a>, <a href="#ref-8">8</a>]. Capillaria species (hairworms) infect the crop, esophagus, and intestine, causing severe enteritis and weight loss [<a href="#ref-7">7</a>, <a href="#ref-8">8</a>]. Syngamus trachea (gapeworm) resides in the trachea, causing respiratory distress, coughing, and gasping [<a href="#ref-7">7</a>]. Tetrameres species infect the proventriculus, leading to glandular dysfunction [<a href="#ref-7">7</a>].
Cestodes
Cestodes (tapeworms) require an intermediate host (e.g., beetles, flies, earthworms) for transmission. Raillietina species (R. tetragona, R. cesticillus, R. echinobothrida) and Choanotaenia infundibulum are common in the small intestine [<a href="#ref-1">1</a>, <a href="#ref-7">7</a>]. Davainea proglottina is a highly pathogenic cestode that causes severe enteritis [<a href="#ref-7">7</a>]. Hymenolepis species are also reported [<a href="#ref-7">7</a>].
Trematodes
Prosthogonimus species (flukes) infect the oviduct and bursa of Fabricius, causing egg peritonitis and reduced egg production [<a href="#ref-1">1</a>]. Trematodes require a snail intermediate host for transmission.
Protozoan Parasites
Coccidia
Eimeria species are the most important protozoan parasites of poultry, causing coccidiosis [<a href="#ref-9">9</a>, <a href="#ref-10">10</a>]. Eimeria tenella, E. necatrix, E. acervulina, E. maxima, and E. brunetti are the major pathogenic species [<a href="#ref-9">9</a>]. Coccidiosis is characterized by diarrhea, bloody droppings, reduced feed conversion, and mortality [<a href="#ref-10">10</a>]. Cryptosporidium species are also reported in poultry, with potential zoonotic implications [<a href="#ref-8">8</a>].
Haemoparasites
Plasmodium species (avian malaria), Haemoproteus species, and Leucocytozoon species are blood-borne protozoa transmitted by insect vectors [<a href="#ref-11">11</a>]. Leucocytozoon caulleryi is a significant pathogen in East and South Asia, causing anemia, leukopenia, and mortality [<a href="#ref-3">3</a>]. Plasmodium gallinaceum causes severe disease in chickens [<a href="#ref-11">11</a>].
Flagellates
Histomonas meleagridis causes histomonosis (blackhead), characterized by necrotic typhlitis and hepatitis [<a href="#ref-3">3</a>, <a href="#ref-8">8</a>]. Tetratrichomonas gallinarum is a related flagellate that causes enteritis [<a href="#ref-8">8</a>]. Blastocystis species are commonly detected in poultry but their pathogenic role is unclear [<a href="#ref-8">8</a>].
Chicken Parasites in Eggs
Several parasites can be transmitted via the egg. Ascaridia galli eggs can be shed in feces and contaminate the eggshell surface [<a href="#ref-6">6</a>]. Capillaria eggs can be present in the egg contents if the oviduct is infected [<a href="#ref-8">8</a>]. Eimeria oocysts are not typically found in eggs but can contaminate the shell surface from fecal material [<a href="#ref-9">9</a>]. Cryptosporidium oocysts can be present on eggshells and pose a zoonotic risk [<a href="#ref-8">8</a>]. Prosthogonimus flukes directly infect the oviduct, leading to egg abnormalities and fluke eggs in the egg contents [<a href="#ref-1">1</a>].
Chicken Parasites in Meat
Parasites in poultry meat are primarily a concern for food safety. Ascaridia galli and Capillaria species can cause carcass condemnation due to visible lesions [<a href="#ref-6">6</a>]. Eimeria species do not infect humans but cause economic losses due to reduced meat quality [<a href="#ref-9">9</a>]. Cryptosporidium species are zoonotic and can be transmitted via undercooked meat [<a href="#ref-8">8</a>]. Toxoplasma gondii can be present in poultry meat and is a significant foodborne pathogen [<a href="#ref-12">12</a>].
Diagnostic Approaches
Diagnosis of poultry parasites relies on a combination of clinical examination, necropsy, and laboratory techniques.
Fecal Examination
Fecal flotation (using saturated salt or sugar solutions) and sedimentation are standard methods for detecting nematode eggs and coccidian oocysts [<a href="#ref-7">7</a>, <a href="#ref-8">8</a>]. The McMaster counting chamber is used for quantitative egg counts [<a href="#ref-8">8</a>]. Modified Sloss technique is used for trematode eggs [<a href="#ref-7">7</a>].
Necropsy
Direct visualization of adult worms in the intestine, ceca, and trachea is performed at necropsy [<a href="#ref-6">6</a>]. Ascaridia galli adults are 2-12 cm long, Heterakis gallinarum are 0.5-1.5 cm, and Capillaria species are thread-like [<a href="#ref-6">6</a>].
Molecular Diagnostics
PCR and qPCR are used for species-specific detection of Eimeria, Histomonas, Cryptosporidium, and Blastocystis [<a href="#ref-8">8</a>]. High-throughput sequencing can identify mixed infections [<a href="#ref-11">11</a>].
Serology
ELISA for Dermanyssus gallinae antibodies is used for monitoring mite exposure [<a href="#ref-3">3</a>].
Treatment and Control
Anthelmintics
Fenbendazole is the only approved benzimidazole for poultry ascarids [<a href="#ref-6">6</a>]. Resistance has been reported in Ascaridia galli and Heterakis gallinarum [<a href="#ref-6">6</a>]. Levamisole and piperazine are also used but have variable efficacy [<a href="#ref-6">6</a>]. Ivermectin is used off-label for ectoparasites [<a href="#ref-4">4</a>].
Anticoccidials
Ionophores (monensin, salinomycin) and synthetic compounds (toltrazuril, diclazuril) are used in feed [<a href="#ref-9">9</a>]. Live vaccines using precocious or attenuated Eimeria strains are available [<a href="#ref-3">3</a>, <a href="#ref-9">9</a>].
Ectoparasite Control
Pyrethroids, organophosphates, and carbamates are used for mite and lice control [<a href="#ref-4">4</a>]. Diatomaceous earth and sulfur dust are used in organic systems [<a href="#ref-4">4</a>].
Biosecurity
Strict quarantine, cleaning, and disinfection are critical for preventing parasite introduction [<a href="#ref-8">8</a>]. Litter management and rotational grazing reduce environmental contamination [<a href="#ref-10">10</a>].
Mermaid Diagram: Diagnostic Workflow for Poultry Parasites
flowchart TD
A["Clinical Signs: Diarrhea, Weight Loss, Anemia, Respiratory Distress"] --> B["Fecal Sample Collection"]
B --> C["Fecal Flotation / Sedimentation"]
C --> D{"Positive for Eggs or Oocysts?"}
D -->|"Yes"| E["McMaster Count / Species ID"]
D -->|"No"| F["Necropsy / Direct Visualization"]
F --> G{"Adult Worms or Lesions?"}
G -->|"Yes"| H["Species Identification / Morphology"]
G -->|"No"| I["Molecular PCR / qPCR"]
I --> J["Species Confirmation"]
E --> K["Treatment Selection"]
H --> K
J --> K
K --> L["Anthelmintic / Anticoccidial / Ectoparasiticide"]
L --> M["Post-Treatment Fecal Exam"]
M --> N{"Parasite Clearance?"}
N -->|"Yes"| O["Biosecurity / Prevention"]
N -->|"No"| P["Resistance Testing / Alternative Drug"]
P --> K