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Field Note: Looking a Gift Possum in the Mouth

By Mike Kinsella

Fig. 1: Eggs tracks of Anatrichosoma in the palate of an opossum. From Pence and Little (1972) in Journal of Parasitology.

In 1972 in the Journal of Parasitology, Pence and Little described a new species of nematode, Anatrichosoma buccalis, which lived in tunnels in the mucosa of the palate and tongue of opossums, Didelphis virginia. The golden-brown eggs of the worms could be clearly seen as they were left behind in the tunnels (Fig. 1), where they presumably were sluffed off with tissue change, swallowed and passed out in the feces.

At the time I read the article, I was on a postdoctoral fellowship at the Archbold Biological Station (ABS) in southern Florida. The very next day I was in the field with the resident trapper, Chet Winegarner, to check out any opossums he might catch. Now, if you grab a possum by the neck, he will invariably “gape” at you, showing a mouthful of sharp teeth (Fig. 2). But it is just a threat since possums are not really that aggressive. Very convenient though if you want to get a look at the palate and there, staring us in the face in the very first animal, were obvious egg tracks!

Because of long term mammal studies, most possums at ABS were already ear-tagged and many were “trap-happy,” caught on multiple occasions. And since they conveniently carry their young in a pouch, it would be easy to check when they first became infected. We (mostly Chet) could monitor infections over time without the need to run messy fecals.

Prevalence in adults was extremely high- 70% in both males and females, although lesions were not apparent consistently in individuals over time- present in some months and absent in others. Turnover seemed to be quite rapid, with egg tracks disappearing in as little as 3 days. Young were first found infected at 5 months but by 8 months, prevalence approached that of adults.

This was a unique opportunity to follow a parasitic infection in the field without sacrificing any hosts. We could definitively say that no animals were harmed in the course of this study. In fact, they all seemed to be smiling!



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