Diagnostic Methods for Candida albicans Infection in Deer

Candida albicans, as an opportunistic pathogen, can normally exist in the oral mucosa, gastrointestinal tract, anus, vagina, skin and other parts of humans and animals, and generally does not cause disease. However, when the body suffers from malnutrition, vitamin deficiency, or long-term use of antibacterial drugs, the probability of Candida albicans infection increases, and in severe cases it can lead to infection of other organs, illness, or even death. Single infection with animal-derived Candida albicans rarely occurs; it is generally a mixed infection. Because its harmfulness is not great, it generally does not easily attract the attention of the breeding industry and veterinary workers. There are only reports of Candida albicans infection in meat breeding pigeons, broiler chickens, etc. raised on a few farms, but no economic losses were caused. When our laboratory was identifying a batch of diseased materials from a deer farm in Shuangyang, Changchun City, a pathogenic strain of Candida albicans was isolated from them. The report is as follows.

1 Incidence and Collection of Diseased Materials

At a deer farm in Changchun City, about 6.1% (8/131) had diarrhea of varying degrees. After clinical guidance and medication by the farm veterinarian (florfenicol injection + Tuire Shenzhen + multivitamins), some improved and recovered, while the remaining 3 had intractable diarrhea that did not stop. The affected deer were depressed, with messy coat, emaciated, and obviously malnourished. Body temperature was 40-41.5°C. The area around the anus was filthy, and the feces were bean curd residue-like, containing small bubbles. Cotton swabs were used to collect anal dirt and feces.

2 Laboratory Examination

2.1 Smear Staining and Microscopic Examination

The diseased materials were treated with normal saline, stained by Gram staining, and examined microscopically. Most were seen to be Gram-positive, with uneven staining, having clustered blastospores and pseudohyphae, with budding cells oval, resembling yeast cells. There were also a small number of Gram-negative bacteria, red, short and rod-shaped.

2.2 Pathogen Isolation and Culture

After treatment with normal saline, the diseased materials were directly streaked and inoculated onto Sabouraud agar medium plates, cornmeal Tween agar medium plates, and BTB plates for culture. Then, according to differences in colony morphology, single colonies were picked and purified. The results showed that on Sabouraud agar medium, colonies cultured at 37°C for 48 h were cream-colored, yeast-like, round, with neat edges, raised centers, moist and smooth. The culture from these colonies was taken and examined microscopically after Gram staining, and clustered blastospores and pseudohyphae were visible. On cornmeal Tween agar after culture at 37°C for 48 h, colonies were picked and examined microscopically after Gram staining, and true hyphae, pseudohyphae, and blastospores were visible. On BTB medium, after fermenting glucose, the green plate turned yellow, forming small round colonies with neat edges.

2.3 Biochemical Tests

The bacterial solution purified on Sabouraud agar medium plates and cornmeal Tween agar medium plates was inoculated with an inoculating loop into glucose, maltose, lactose, galactose, sucrose, fructose, mannitol, and sorbitol, and cultured at 37°C for 24 h. The results showed that the fungus could utilize glucose, maltose, and fructose, producing acid and gas; utilize sucrose and galactose, producing acid but not gas; and could not utilize lactose, mannitol, or sorbitol. The small colonies growing on BTB medium were not subjected to biochemical tests.

2.4 Animal Tests

Four mice were taken and divided into two groups. The experimental group had 2 mice, which were inoculated subcutaneously in the neck with bacterial solution cultured within 24 h, and the control group had 2 mice, which were injected intraperitoneally with normal saline. The experimental mice showed an inflammatory reaction at the inoculation site after 3 h; redness and swelling appeared at the inoculation site after 5 h; and the redness and swelling markedly worsened after 7 h. The experimental mice were depressed and had mild diarrhea. The control mice had no abnormal reactions. On the 5th day, the rabbits were killed. The abscess site was cut open, and the abscess fluid was seen to be viscous. The abscess fluid was taken, smeared, Gram-stained, and examined microscopically, and the pathogen morphology was found to be the same as before. Necropsy of the dead rabbits showed obvious enlargement of the kidneys and liver, which were covered with uniformly sized, pinhead-sized abscesses, with the lesions in the renal cortex being the most obvious. In addition, the spleen was enlarged, the lungs were shrunken, the entire intestinal tract was obviously distended with gas, and there was yeast-smelling exudate in the abdominal cavity. The control rabbits all showed no abnormalities.

2.5 Drug Sensitivity Test

Drug sensitivity tests were conducted on this fungus on Sabouraud agar culture dishes using commonly used veterinary antifungal drugs such as fluconazole, ketoconazole, itraconazole, nystatin, amphotericin B, and clotrimazole. The results showed that the fungus was highly sensitive to itraconazole and nystatin; moderately sensitive to fluconazole and amphotericin B; weakly sensitive to clotrimazole and ketoconazole; and basically unaffected by commonly used antibiotics.

3 Diagnosis

Based on laboratory isolation and identification, combined with clinical symptoms, necropsy changes in experimental animals, and drug sensitivity test analysis, the comprehensive diagnosis was Candida albicans infection in this case.

4 Summary

As an opportunistic pathogen, Candida albicans is mostly an endogenous infection. Long-term and large-scale use of broad-spectrum antibiotics, combined with poor environmental hygiene, leads to imbalance of the normal flora in livestock and poultry bodies, becoming one of the causative factors. In production work, as long as management is strengthened, environmental hygiene is improved, and scientific feeding is carried out, this disease can be avoided. Mixed infection of deer with Candida albicans has begun to emerge, and should attract the attention of workers at deer farms.