Microsporidial infections in humans: current practice and developments in laboratory diagnosis

Microsporidia are small, intracellular parasites that infect a wide range of hosts, including vertebrates, invertebrates and fish. They were discovered more than a century ago. The first well documented human case, however, was not reported until 100 years later. Since the first case of intestinal microsporidiosis was reported in 1985, numerous cases of microsporidiosis have been reported in immunocompromised patients, especially those in the later stages of human immunodeficiency virus (HIV) infection. Microsporidia also have been described in various other clinical conditions, including keratoconjunctivitis, sinusitis, peritonitis and myositis. The numbers of cases reported have risen dramatically since 1985, which can be explained partly by the acquired immune deficiency syndrome (AIDS) pandemic and partly by increased laboratory awareness. Some studies have shown that up to 50% of selected AIDS patients are infected with microsporidia. Diagnosis depended initially on the use of invasive techniques, namely histological examination of biopsy material. Since then, however, there have been important advances in the detection of microsporidial spores in clinical samples. Recent developments in the diagnosis of microsporidiosis are described, including light microscopy staining methods, fluorescent staining, electron microscopy and molecular techniques.