OTOSTRONGYLUS INFECTION

Tavishi One of the chief concerns among elephant seals presenting at the Marine Mammal Center is a nematode (roundworm) parasite known as Otostrongylus circumlitus. The infection caused by O. circumlitus is known clinically as otostrongyliasis. This is Oranna, a Northern elephant seal admitted to the Marine Mammal Center in 2019 for lungworm!

O. circumlitus are metastrongyles, or lungworms, affecting primarily phocid seals (earless seals including harbor seal, harp seal, bearded seal, and Northern elephant seal.) Infection of these worms occurs in different parts of the body depending on species. While harbor seals primarily experience infection within the branchioles, Northern elephant seals have adult worms within the right ventricle and pulmonary arteries. The primary clinical symptom of O. circumlitus within the Northern elephant seal is disseminated intravascular coagulation, or DIC for short. Disseminated intravascular coagulation is excessive clotting within blood vessels. As you may be able to guess, it's not fun to deal with DIC, either as a patient or a provider treating the infection.

Blood parameters indicating DIC include low albumin and a low albumin to globulin ratio. While a normal albumin level would be 3 g/dL, abnormal albumin levels indicative of potential O. circumlitus infections would fall below 2.5 g/dL. Similarly, elevated neutrophil, with a >13 g/dL concentration within blood plasma, would indicate O. circumlitus as well. However, nothing is particularly unique about these blood parameters within O. circumlitus compared to other infections other than signs of inflammatory response and anemia. Rather, an increase in activated partial thromboplastin time and prothrombin time are most indicative of the extremely dangerous symptom DIC.

PT and APTT measure the amount of time for blood clotting. Prothrombin is the precursor to thrombin, the active form of prothrombin which creates fibrin from fibrinogen. This thus creates blood clots.

The image above is NOT a blood clot, contrary to popular belief!

In any individual, a normal PT and APTT time is important. In severe DIC, which is seen within Northern elephant seals with O. circumlitus, the excessive clotting essentially uses up the clotting factors, which then leads to serious hemorrhaging because of an inability to clot. As a result, PT and APTT are high. However, at this point in O. circumlitus infection, DIC is nearly impossible to prevent, at which point veterinarians are at an utter loss. O. circumlitus diagnostic techniques are kind of limited, as we haven't done nearly enough research. (cough cough gap in the literature?!?!) However, the Marine Mammal Center, in addition to countless marine mammal veterinarians (Zeehondcentrum Pieterburen, UC DAVIS, and MORE!!) around the world are working tirelessly to continue to study lungworm. The transmission of O. circumlitus is characteristic of any parasitic worm or just parasite in general- see: toxoplasmosis, U. sanguinis (I wrote a paper about this!).

First stage larvae are passed into faeces. At this point, the larvae are not infective to seals, but are infective to fish. I'm not entirely sure why, but I intend to figure it out. Anyways, the larvae then mature within the fish, and then said fish are eventually eaten by seals. When the larvae are third-stage, they can cause infection within the seals. Larvae then migrate from the gastrointestinal tract to the cardiovascular and pulmonary systems depending on the species of seal. At this point, infection is prepatent (does not demonstrate symptoms).

Once migrated, however, infection becomes patent and symptoms become apparent. This post is a cautionary tale. If you're a phocid, beware the fish you ingest, or your fate may be sealed by some tyrannical, greedy worms.