Pathogenicity and virulence of <i>Cryptosporidium</i>

<i>Cryptosporidium</i> is a genus of apicomplexan parasites that causes diarrheal disease in humans and animals worldwide. The primary species affecting humans are <i>C. parvum</i> and <i>C. hominis</i>, while other species may also infect humans, specially immunocompromised individuals. Infections are particularly severe in people with weakened immune systems and malnourished children in developing countries. In livestock, especially young ruminants, <i>C. parvum</i> leads to significant economic losses. The parasite occupies a unique epicellular niche and undergoes a complex life cycle involving both asexual and sexual stages. While the mechanisms of parasite invasion, replication, immune evasion, and tissue damage have been challenging to unravel due to earlier technical limitations and lack of genetic tools, recent advances have transformed our understanding. Innovations in genomics, transcriptomics, and molecular genetics have identified key virulence factors and clarified intricate host-parasite interactions. The parasite's secretory organelles (micronemes, rhoptries, dense granules, and small granules) play central roles by releasing molecules that facilitate host cell attachment, invasion, and modulation of host defenses. This review provides an up-to-date overview of the biology and pathogenic mechanisms of <i>Cryptosporidium</i>, highlighting structural features, invasion strategies, and host immune responses. It also covers recent progress in experimental models, vaccine development, and identification of new molecular targets for treatment and prevention. By synthesizing recent discoveries with previous research, this review offers a current perspective linking fundamental biology to disease outcomes and potential control strategies.