Stranded beluga whales (Delphinapterus leucas) from the St.
Lawrence estuary were examined for the cranial sinus nematode, Pharurus pallasii (van
Beneden, 1870) Arnold and Gaskin 1975. Analyses indicated that 87% of all stranded adult beluga
(>7 years old, N=30) are infected (mean intensity=340, range" 1-2042), 67% of stranded
juvenile beluga (1 to 7 years old, N=3) are infected (mean intensity=15, range: 2-28) and none
of the young of the year (<1 year old, N=5). The prevalence of infection was similar in male
and female adult beluga, namely, 87%. There is a statistically significant difference in mean
intensity of infections between male adult beluga (mean intensity=577, N=15) and female adult
beluga (mean intensity=199, N=I 5).
Fifth-stage worms were found in the pterygoid sinuses and peribullar (ear)
sinuses. The worms were equally distributed between the left and right sinuses (worms in
pterygoid and peribullar sinuses together on each side compared to that on opposite side).
However, parasites were four times more numerous in the peribullar sinuses compared to the
pterygoid sinuses. Female P. pallasii were twice as numerous as males and significantly
larger (mean female length: 27.9 + 3.8 mm; mean male length: 21.2 + 2.9 mm). No mucosal or bony
macroscopic lesions were observed in association with P. pallasii even in beluga with
heavy infections (i.e. >2000 worms). The lungs were systematically examined for adult P.
- none was observed (N=25).
This study demonstrates that the cranial sinuses are the principal niche of
P. pallasii. We had hypothesized that host sex had no effect on the intensity of
infection. Our preliminary data, however, indicates that the sex of the host influences the
intensity of infection (the mean intensity of infection of P. pallasii in adult male
beluga was almost three times greater than that in adult female beluga). Absence of this
parasite in nursing calves, the low intensity of infection in juveniles and high intensities of
infections in adults suggest a heteroxenous life cycle for P. pallasii (i.e. more than
one host is required for the transmission and development of this parasite). These observations
lead to the testable hypothesis that beluga acquire infections of P. pallasii through the
intake of infected food. There is no evidence of transplacental transmission of P. pallasii
as suggested for some pseudaliids in odontocetes.