Marine Mammal Parasite of the Month – Answer February 2012

The parasite is Nasitrema attenuata.

The distinguishing characteristics include compatible length and maximum width, lack of pre-acetabular vitellaria, weakly lobed testies and ovary divide into 2-4 blunt lobes (Neiland, et al., 1970).

The parasite is implicated for several type of disease.

1) Irritation and competition for nutrients, mostly likely not a component of diseases without unusually high colonization rates.

2) Migration into the brain along a nerve tract; any CNS involvement can cause fatal acute disease and serious chronic medical problems.

3) Chronic pulmonary irritation and inflammation from inhaling the eggs, which act as small foreign objects, deep into the bronchial tree.

(Chronic sterile interstitial pneumonia with nodules) – Kumar et al., 1975.

But it gets worse….

4) The migration of Nasitrema along the 8th cranial nerve, with eggs embedded into the crevices of the nerves (Morimitsu et al., 1992).

And still worse….

Additionally, adult Nasitrema have been found in brain tissue with both chronic and acute lesions (Daily and Walker, 1978) easily capable of causing strandings.

Nasitrema encephalitis (O’Shea et al., 1991) may be the most extreme form, but infection occurs in the air sinus, brain, and even in the umbilical artery (Daily and Walker, 1978).

So a full account of the effect on strandings requires a full necropsy with a complete gross and histological examination of the brain and 8th cranial nerve.

A diagnosis of infection can be made by examining the “blow” from a captive cetacean looking for the characteristic golden brown triangular eggs.