Gastrointestinal infection: The combination of abdominal pain, elevated monocytes, and a high white cell count suggests an infectious process, with gastrointestinal infection being a common cause. Parasites, as suspected, could be a culprit, but bacterial or viral infections are also possible.

Inflammatory bowel disease (IBD): Conditions like Crohn's disease or ulcerative colitis can cause abdominal pain and elevated inflammatory markers, including an increased white cell count and monocytes.
Diverticulitis: An inflammation of the diverticula in the digestive tract, which can cause abdominal pain and an elevated white cell count.
Appendicitis: Although typically presenting with neutrophilia, some cases can have a significant monocyte response, especially if the condition is progressing or if there's an associated infection.

Intestinal obstruction: Can cause severe abdominal pain and may lead to an elevated white cell count due to associated ischemia or infection. Early diagnosis is crucial to prevent bowel necrosis.
Perforated viscus: A hole in the wall of the digestive tract can lead to peritonitis, which presents with severe abdominal pain and an elevated white cell count. Prompt surgical intervention is necessary.
Mesenteric ischemia: Reduced blood flow to the intestines can cause abdominal pain and an elevated white cell count. It's a medical emergency requiring immediate attention.

Whipple's disease: A rare, systemic bacterial infection that can cause abdominal pain, weight loss, and an elevated white cell count. Diagnosis is often delayed due to its rarity and nonspecific symptoms.
Abdominal lymphoma: Can cause abdominal pain and an elevated white cell count, including monocytes, due to the disease process or associated infections.
Eosinophilic gastroenteritis: Although more commonly associated with eosinophilia, some cases can present with elevated monocytes, especially if there's a significant inflammatory component.