Kimberlee B. Beckman, DVM, MS; Judith Gerber, DVM; Murry Dailey PhD; Linda
Lowenstine, DVM, PhD; Laurie J. Gage, DVM
Otostrongylus circumlitus (Railliet, 1899), the large pulmonary
worm of seals, is commonly found in ringed seals, Phoca hispida and Atlantic harbor
seals, Phoca vitulina vitulina, and has been reported in Pacific harbor seals, Phoca
vitulina richardsi, from northern elephant seals, Mirounga angustirostris and a grey
seal, Halichoerus grypus.
In 1992, The Marine Mammal Center (TMMC) handled an unprecedented increase
in stranding calls with a total of 794 patients admitted. Among phocid pups, 0. circumlitis,
showed an increased incidence. 0. circumlitis was infrequently detected in northern
elephant seals, M. angustirostris, at necropsy at TMMC prior to 1990. A total of 5 cases
(13.5%) were documented in 1991. In 1992, it was the leading cause of mortality among M.
angustirostris weaner pups admitted (45.3% of necropsies which represents 39 cases).
Unweaned pups, as young as 8 weeks old, died from fulminating disease with worms up to 14 cm in
length in the respiratory tree and vasculature. Weaned pups were significantly more affected
than other age classes. Among P. vitulina examined post mortem, the infection rate
increased significantly from an historical incidence of 2.4% (from 1984 to 1989), 0.4% in 1991,
to 16.5% in 1992. TMMC has documented the parasite in the hearts of two otariids, juvenile
Zalophus californianus in 1992.
A program to detect infection antemortern and to develop an effective
treatment protocol was hastily instituted mid-pupping season 1992. Fresh feces were collected
and examined for the presence of larvae via a sedimentation concentration technique. Positive
animals were treated with 50 mg/kg body weight with fenbendazole paste (PanacurR) PO SID for 10
to 30 days. Dexamethasone, antibiotics and an oral expectorant (guaifenesin) were also
administered. Animals were nebulized with acetylcysteine and given coupage therapy SID to QID
depending on the severity of clinical signs. Typical clinical signs consisted of: dyspnea with
rales and wheezes, emaciation, hemoptysis, epistaxis, anorexia, pyrexia, depression and
coagulation. Radiographic signs were similar to canine heartworm disease. Gross pathology
revealed severe consolidating pneumonia and lesions consistent with cardiopulmonary collapse and
septicemia.
A severe vasculitis and lesions secondary to verminous pneumonia and were
seen histopathologically. Treatment was successful in a number of Miruounga and two
Phoca. Research is currently being undertaken to determine the life cycle of this
parasite and to further document the pathobiology of the disease.