Diagnosis of Candidiasis in Marine Mammals: Utilization of a Scrape and Agar Technique for Epithelial Infections
How we view the process of diagnosis and therapy, of cause and effect, is influenced by a number of factors. With microbiologic infections we receive countless hours of training in relation to bacterial involvement during our veterinary career. With the fungi and yeast we are often left to our own to learn the basics. While the number of marine animal illnesses and deaths related to yeast is much lower than bacteria it is still an important area of consideration that may go unrecognized and consequently unchallenged.
There are a number of Candida species that may be recovered from marine mammals and they are found in a variety of sites on and in the body. It is generally thought that Candida is a normal inhabitant of many cetaceans usually noted on cultures from the nasal system, or from blow plates, because this is the most common site that is cultured. It is usually present in small numbers and may be missed altogether on surveillance cultures in healthy animals. It can also be found in the intestinal tract but its presence is not usually a sign of pathology. Like some bipedal species it can also be found in the reproductive tract.
As anti-fungal agents have become available for general use there are fewer presentations of what would otherwise be more common problems. Individuals who may have ill animals often use nystatin, or a systemic antifungal agent, to avoid “secondary problems.” We are in effect preventively approaching yeast problems often without the knowledge of the variety of presentations possible.
Classic descriptions of candidiasis in cetaceans may involve accumulations of debris in the nasal area or linear ulcerations in the esophagus. Without the benefit of endoscopy, or the use of antifungals, these might be a postmortem diagnosis. Over time, with more individuals to study and compare, it is apparent that there are more clinical presentations that may go unrecognized with typical culture techniques. Visual indicators of candidiasis around the external nares include a change in coloration of the epithelium to a lighter shade. In the oral cavity there may be circular, to ovoid, to diffuse changes in the mucosa. These also include a paler color and roughening of the texture of the epithelium. Linear esophageal ulcerations are still found in some individuals who are chronically debilitated. Affected vaginal mucosa may appear roughened and penile epithelium may have ovoid or circular lesions. In pinniped species such as walrus, there may be persistent lesions in the skin, or in the folds of the flippers similar to an ulcerative dermatitis.
Typical diagnostic approaches with cotton tip culturettes or cytology are often unrewarding and may be misleading. Biopsy is more productive but less desirable when considering the locations involved or the need to sedate the animal. In addition, there is often reluctance to sample these sites because of the need to restrain and handle the animal. An alternative method is to combine portions of two diagnostic approaches. A small flat chemical spatula that has a sharper edge on the concave side is used to do a deep scraping of the abnormal tissue. Where before this would be used for cytology attempts instead it is applied directly to the mycotic plate slicing into the agar. This technique results in a higher chance of tissue recovery and enhances the chance of positive culture results. With initial attempts additional scrapings were done in surrounding normal tissue to show that the technique was not picking up normal flora. All surrounding scrapings were negative. Positive scrapings of lesions usually resulted in a line of Candida colony growth along the agar slice.
With oral lesions involving the tongue or hard palate three cetaceans were put on nystatin initially. With these trained animals the nystatin was applied and the animals maintained in a heads-up position to avoid flushing out the drug for up to 5 minutes. While there was some improvement in the visual appearance of the lesions over a number of weeks there was not a total resolution. This may have been partially due to the inability to maintain a sufficient amount of contact time on the affected sites, or an indication that the infection was too deep for good drug contact. The addition of a systemic antifungal agent, usually itraconazole, resulted in clearing of the lesions.
It should be emphasized that cytology and culture are still mainstay approaches for other sites such as blow cultures and fecal evaluation. This technique is not a substitute but can be used as an additional diagnostic aid where standard culture attempts have not been efficient, where the condition is non-responsive to bacterial therapy, or where biopsy is not considered a desirable alternative.