Pathological effects of Cryptocotyle lingua in double-crested cormorants (Phalacrocorax auritus) treated with dexamethasone

An association between large proportions of intestinal parasites, particularly trematodes, found in dead emaciateû cornmon loom (Govio immer) and other avian species, suggests that parasites can cause or contribute to a debilitating proces that results in the demise of wild, fiee-ranging seabirds. Since concurrent etiologies can contribute to the mortality of seabirds, determination of the temiinal cause of death is a wmplex process, particularly in chronically debilitated birds. Evaluation of the effects of a single etiology helps assess the extmt of its involvement in the death of the birds. One observation reported in dead common loons, the large numbers of Cryptocotyle lingua found in weak birds, suggests that an underlying disease problern may cause impairment of the immune system of the birds that leads to an increased degree of parasitism, causing Mer debilitation. This study intended to replicate the infection caused by C. lingun, an intestinal trematode nomally present in small numbers in adult seabirds that die in good body condition, with no signs of a debilitating disease. Replication of the infection caused by C. lingua was conducted in immunocompetent and immunosuppressed seabirds, specifically doublecrested comorants, Phalacrocorax aunlus. The birds were collected hm a wild colony at 2 weeks of age and raised in captivity until the experimental trial began at 2 months of age. A total of 31 doublecrested cornorants @CC) were divided into 4 different treatment pups: an immunosuppressed/infecteâ group (n=8), an immunosuppressed/nnon-infected group (n=7), a non-immunosuppressed/infected group (n=8) and a non-inimunosuppressed/non-infected group (n=8). The immunosuppression of the birds involved administration of dexamethasone before and during the experimental infection with C. lingua and was confïnned through evaluation of the cellular and humoral responses. A phytohemagglutinin-P skin test showed that DCC treated with dexarnethasone had an impairecl T ce11 response (pe0.01). A slightly decreased production of antibodies against sheep red blood cells (SRBC) @<0.05), and severe lymphoid depletion of the bursaofFabricius in treated DCC (pC0.0 1) indicated a detrimental effect on humoral irnmunity caused by dexamethasone. Heterophilia was ah associated with the treatment with dexarnethasone. Infection of the DCC was accomplished by oral administration of large numbers of C. linguu metacercariae. A previous pilot study showed that the administration of metacercariae obtained fkom the fins and tails of fish that inhabit the waters around Prince Edward Island, Canada, successfiilly produces an infection in DCC. Adult C. lingua are present in the DCC 4 days afler inoculation of the metacercariae me-patent period) and can rernain there for at least 6-7 days (patent period). An increase in the total number of adult C. Iinguu found in the intestine of immunosuppressed DCC suggests that a decreased immune response leads to higher parasite loads in seabirds. However, no pathological or clinical effects were observeâ in association to the parasite, which seems to indicate the benign nature of infection by C. lingua.