Cross-sectional study of faecal shedding of Giardia duodenalis and Cryptosporidium parvum among packstock in the Sierra Nevada Range.

This research studied how often feces from pack animals (like horses and mules) in the Sierra Nevada Range were found to contain certain parasites. It found that a small number of the animals were shedding a specific cyst, while none were shedding a different, potentially harmful one.

Study Design and Methods

• The researchers collected fecal specimens from a total of 305 horses and mules. These animals were used as packstock in either commercial or governmental operations, including ones run by the National Park Service and the US Forest Service.
• The specimens were examined for two specific parasites: Giardia duodenalis and Cryptosporidium parvum. The researchers used a method known as fluorescent microscopy to detect these parasites in the samples.

Key Findings

• The study found that 14 of the packstock (approximately 4.6%) were shedding G. duodenalis cysts. The term “shedding” refers to the process through which an infected animal releases the parasites into the environment through their feces.
• The prevalence of shedding varied widely among different herds, ranging from 0% to 22%. Several factors were associated with the likelihood of an animal shedding these cysts, including the number of packstock in a corral, the size of the corral, and the density of packstock within it.
• Interestingly, none of the horses were found to have detectable C. parvum oocysts, which are a different life stage of the parasite. This is significant because C. parvum can cause disease in humans and many animal species.
• The researchers estimated that the maximum true prevalence of C. parvum shedding among the packstock would be less than or equal to 2.3%, assuming a sensitivity of at least 43% and a specificity of 100% for their testing method.

Conclusion and Implications

• The findings suggest that it is unlikely that packstock are significantly contributing to the spread of C. parvum in the backcountry watersheds of the Sierra Nevada Range through their feces. This is reassuring given the potential for this parasite to contaminate water sources and cause disease.
• However, the occurrence of G. duodenalis shedding highlights the need for continued monitoring and management of these animals to reduce the risk of parasite transmission.