Abstract

Otostrongylus circumlitis is a lungworm infecting Northern elephant seals (Mirounga angustirostris) and a significant cause of mortality among stranded juveniles along the central coast of California. Mortality frequently occurs during the pre-patent period, preventing reproduction in the host; thus, ante-mortem diagnosis is difficult as fecal identification is not sensitive.¹ Infected juvenile elephant seals generally develop non-specific clinical signs caused by pulmonary arteritis and/or disseminated intravascular coagulation (DIC).¹ At The Marine Mammal Center (Sausalito, CA), 26% of total Northern elephant seal mortalities are due to O. circumlitis (OC) infections. Most patients are unable to recover from clinical disease despite aggressive treatment, and are diagnosed with the parasitic infection upon necropsy. Earlier and more sensitive diagnostic techniques are needed to detect and treat this disease successfully.

Acute-phase proteins (APP) are integral to the acute-phase response (APR) and innate immunity.² Over the last couple of decades, these proteins have become increasingly important in detection of early inflammation in humans and animals. C-reactive protein (CRP) and albumin:globulin (AG) ratios are useful inflammatory biomarkers in many domestic and non-domestic species including cows, dogs, manatees, elephants and harbor seals; however, variability in dominant APP type and APR magnitude is species-specific, and no published information is available regarding these markers in Northern elephant seals.^3-7 The objective of this study was to identify differences in APP levels between healthy, malnourished, and OC-infected Northern elephant seals, and to determine if these assays can be utilized as early diagnostic tools to detect disease before animals develop clinical signs. It was hypothesized that infected animals have higher CRP concentrations and lower AG ratios than malnourished or clinically healthy animals.

Protein electrophoresis and CRP assays were validated and performed on banked serum collected from Northern elephant seals admitted to The Marine Mammal Center between 2012 and 2014. Samples were selected based on specific clinical criteria and organized into three groups: healthy individuals upon release back into the wild (n = 23), malnourished individuals upon admission to the center without clinical evidence of OC infection (n = 23), and individuals that died in treatment or were euthanized and diagnosed with OC upon necropsy (n = 23). Results are presented in Table 1. The main statistically significant differences of OC-infected individuals include the following: total protein and beta globulins were higher compared to malnourished; globulins, alpha-2 and gamma globulins were higher compared to healthy and malnourished, and CRP was higher compared to healthy animals. Alpha-1 globulins were lower compared to malnourished, and albumin and AG ratios were lower compared to healthy and malnourished animals. These findings indicate characteristic changes in protein fractions in OC-infected elephant seals, which were also visible upon evaluation of protein electrophoretograms when compared to healthy individuals (Figures 1 and 2).

Table 1. Mean (range) concentrations of C-reactive protein (CRP) and plasma protein fractions in healthy, O. circumlitis-infected, and malnourished Northern elephant seals. Superscripts represent the groups that the values are significantly different from.

Figure 1. Example of a plasma protein electrophoretogram of a healthy elephant seal

Figure 2. Example of a protein electrophoretogram of an OC-infected elephant seal with characteristic increases in alpha-2 and gamma globulins

Based on these results, protein electrophoresis and CRP have potential to serve as early diagnostic tools in detection of OC infection, allowing earlier treatment and potentially higher survival rates. Future research includes determining how early in the disease process these increased concentrations of APPs can be detected.

* Presenting author
⁺ Student presenter

Literature Cited

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