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By: Wildlife Futures Team Date: Oct 14, 2021

Great Blue Heron on snag - by Jacob Dingel 
Great Blue Heron on snag - Photo by Jacob Dingel, courtesy of the Pennsylvania Game Commission.


Other names: Verminous peritonitis, eustrongylidiasis


Eustrongylidosis is a parasitic disease caused by nematodes in the Eustrongylides genus, including E. tubifex, E. ignotus, and E. excisus1. The parasites have a complex multi-stage life cycle that requires two intermediate hosts and a definitive host.  Wading birds, including herons and egrets, are common definitive hosts of E. ignotus, the species most prevalent in the US. E. tubifex is less prevalent in the US, but has been found in loons, cormorants, mergansers, mallards and eagles, and E. excisus is found in grebes, cormorants, herons, ibis and eagles in Asia2.


While individual birds of any age class can contract Eustrongylides nematodes, the most significant mortalities from the disease occur at communal nesting rookeries where large die-offs of young birds may result from infection with E. ignotus1,2,3. Morbidity and mortality are less commonly associated with E. tubifex infection, and rarely with E. excisus.2

Species Affected

Wading birds in the order Pelecaniformes1,2,4 (including herons, egrets, pelicans, ibis) are most commonly affected, but infections among other piscivorous orders, including Suliformes (cormorants), Gaviiformes (loons), Anseriformes (mergansers), Gruiformes (cranes), Podicipediformes (grebes), Chardriiformes (gulls), and Accipitriformes (eagles) have also been recorded1,2,5,6.  Domestic or captive birds can become infected with Eustrongylides nematodes through the feeding of fish or invertebrates that are infected1,2.  Larval forms of Eustrongylides spp. have also been found in wild mammals, reptiles, and amphibians with no known pathology or clinical disease2.

Human and domestic pet infections are uncommon2. The primary means of contracting Eustrongylides is from consuming raw or undercooked fish that carry the larvae1.  As the larvae are large enough to be visible, most human cases are the result of eating baitfish in high-risk locations. Human cases are reported to be painful and require treatment, including surgery to remove the large adult nematodes2,7.


The three Eustrongylides species known to cause disease (E. tubifex, E. ignotus, and E. excisus) have a combined distribution across all continents except Antarctica.  E. tubifex and E. ignotus are known to inhabit North America, with E. excisus occurring most commonly in Asia2.


All three of the Eustrongylides species have a similar life cycle.  A definitive host bird sheds nematode eggs into the environment which are consumed by aquatic worms that serve as the first intermediate host.  The eggs hatch within the aquatic worms and grow into first and second stage larvae.  Fish that consume the worms containing nematode larvae are the second intermediate hosts. Inside the fish the nematode larvae grow into their third and fourth stages of development.  In the fourth stage of development the larvae are infectious to birds that consume the infected fish.  Larger fish as well as aquatic amphibians and reptiles that consume fish containing infectious larvae can serve as transport hosts that can infect birds that then consume them1,2.

Infectious fourth stage larvae can penetrate the stomach (ventriculus) of a bird within 3-5 hours after consumption of their intermediate or transport host. The larvae undergo rapid maturation in the bird and the sexually mature nematodes begin to shed eggs 10-17 days later1.

Clinical Signs

Clinical signs of infection are non-specific to Eustrongylidosis. Early in the infection when larvae are penetrating the bird’s stomach, head shaking, labored breathing, difficulty swallowing or regurgitating food may occur1.  A lack of appetite and general weakness have also been observed1,2.

Birds may die of internal hemorrhage or from secondary bacterial infections resulting from bacteria entering through the burrows of the nematode larvae2.

Due to higher death rates among young birds, mortalities from Eustrongylidosis are most commonly encountered during the spring and summer breeding season. Mortalities of infected adult birds can be encountered at any time of year1,6.


In the field, palpation of the stomach (proventriculus and ventriculus) surface through the skin can reveal the presence of the raised tunnels produced by adult nematodes early in an infection. Upon necropsy, these tunnels may be visible on the proventriculus, ventriculus, or intestines and are often covered in yellowish fibrous material.  Fibrinous peritonitis on the interior surface of the coelomic cavity, granulomas in the air sacs and intestines, and the presence of the large, red adult nematodes are also seen. Lesions in chronic or resolving infections may not be as apparent1,2.


There is no known treatment for Eustrongylidosis in wild birds. In captive birds, the use of anthelmintics is not recommended due to the potential negative effects of a large nematode die-off2.  There is no known effective treatment of migrating or encysted larvae8.


Minimizing host exposure to Eustrongylides spp. is the most effective means to minimize infection rates. Nutrient pollution can increase water temperatures through eutrophication to the optimal environmental conditions for Eustrongylides nematodes (20-30˚C or 68-86˚F)1. Maintaining water quality through the reduction of nutrient pollution can reduce intermediate host abundance2

Literature Cited

  1. Friend, M., Franson, J.C. and Ciganovich, E.A. eds., 1999. Field manual of wildlife diseases: general field procedures and diseases of birds. US Geological Survey.
  2. Spalding, M.G. and Forrester, D.J. 2008. Chapter 16 Eustrongylidosis. In (Atkinson, C.T., Thomas, N.J. and Hunter, D.B. eds.) Parasitic diseases of wild birds. John Wiley & Sons.
  3. Caudill, G., Wolf, D., Caudill, D., Brown, J. and Shearn-Bochsler, V.A., 2014. Juvenile wading-bird mortality event in urban Jacksonville, Florida, associated with the parasite Eustrongylides. Florida Field Nat42, pp.108-113.
  4. Kinsella, J.M., Spalding, M.G. and Forrester, D.J., 2004. Parasitic helminths of the American white pelican, Pelecanus erythrorhynchos, from Florida, USA. Comparative Parasitology71(1), pp.29-36.
  5. Wobeser, G.A., 1997. Diseases of wild waterfowl. Springer Science & Business Media.
  6. Ziegler, A.F., Welte, S.C., Miller, E.A. and Nolan, T.J., 2000. Eustrongylidiasis in eastern great blue herons (Ardea herodias). Avian diseases, pp.443-448.
  7. Wittner, M., Turner, J.W., Jacquette, G., Ash, L.R., Salgo, M.P. and Tanowitz, H.B., 1989. Eustrongylidiasis—a parasitic infection acquired by eating sushi. New England Journal of Medicine320(17), pp.1124-1126.
  8. Harms, C.A., 1996, April. Treatments for parasitic diseases of aquarium and ornamental fish. In Seminars in Avian and Exotic Pet Medicine (Vol. 5, No. 2, pp. 54-63). WB Saunders.

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Ranked among the top ten veterinary schools worldwide, the University of Pennsylvania School of Veterinary Medicine (Penn Vet) is a global leader in veterinary education, research, and clinical care. Founded in 1884, Penn Vet is the first veterinary school developed in association with a medical school. The school is a proud member of the One Health initiative, linking human, animal, and environmental health.

Penn Vet serves a diverse population of animals at its two campuses, which include extensive diagnostic and research laboratories. Ryan Hospital in Philadelphia provides care for dogs, cats, and other domestic/companion animals, handling nearly 35,300 patient visits a year. New Bolton Center, Penn Vet’s large-animal hospital on nearly 700 acres in rural Kennett Square, PA, cares for horses and livestock/farm animals. The hospital handles nearly 5,300 patient visits a year, while the Field Service treats more than 38,000 patients at local farms. In addition, New Bolton Center’s campus includes a swine center, working dairy, and poultry unit that provide valuable research for the agriculture industry.