Microsporidia are a group of microscopic, spore-forming parasites that primarily infect the cells of animals, including humans. They belong to the kingdom Fungi and are known for their simple structure, lacking many of the organelles found in other eukaryotic cells. These organisms can cause infections, particularly in individuals with weakened immune systems, such as those with HIV/AIDS. Microsporidia are transmitted through spores, which can be found in contaminated water or food. Once ingested, the spores invade host cells and reproduce, leading to various health issues. Common symptoms of microsporidiosis include diarrhea, weight loss, and abdominal pain, highlighting the importance of proper hygiene and sanitation to prevent infection.