North American Veterinary Licensing Examination (NAVLE) Practice Test

What is the likely diagnosis for a 2-week-old calf exhibiting watery diarrhea and weight loss?

1. Colibacillosis

2. Cryptosporidiosis

3. Coccidiosis

4. Ostertagiasis

The correct answer is: Cryptosporidiosis

The likely diagnosis for a 2-week-old calf exhibiting watery diarrhea and weight loss points to cryptosporidiosis. This disease is commonly caused by the protozoan parasite Cryptosporidium parvum, which is particularly known to affect young calves, usually under 3 months of age. In neonates, cryptosporidiosis manifests as severe diarrhea that can lead to dehydration and significant weight loss, primarily due to the calf’s immature immune system and underdeveloped gut flora when exposed to the parasite. The life cycle of Cryptosporidium is such that it can quickly cause infection in young animals, leading to large amounts of watery fecal excretion. While there are other diseases that could cause similar symptoms in calves, cryptosporidiosis is distinctly known for causing diarrhea in very young calves in particular. Colibacillosis, typically caused by E. coli, often presents with severe diarrhea but is frequent in younger calves particularly during the first week of life. Coccidiosis generally occurs in calves older than 3 weeks and typically presents with a different type of diarrhea. Ostertagiasis is more common in older calves or heifers and is associated with a watery diarrhea but usually appears after the first few months of life