The Statens Serum Institut and the Danish Veterinary and Food Administration are currently investigating a disease outbreak in a company with a microorganism that has so far not been registered as a cause of disease outbreaks in Denmark. It is a species of microsporidia, Enterocytozoon bieneusi. It is believed that the infection occurred through food.
Microsporidia are protozoan parasites belonging to the phylum Microsporidia within which exist over 1000 species classified into approximately 100 genera. These eukaryotic obligate intracellular protozoans have been described infecting every major animal group, especially insects, fish, and mammals (Wittner 1999). Microsporidia have been increasingly recognized as opportunistic pathogens of immunodeficient patients (Weber et al. 1994), especially in Aids patients but it is also becoming increasingly common in immunocompetent individuals (Gainzarain et al. 1998, Lores et al. 2001).
Although during the last decade numerous data related to the epidemiology of this infection in humans and animals have been accumulated, implying a zoonotic nature of these parasites, direct evidence of transmission from animals to humans are still lacking (Deplazes et al. 2000).
Encephalitozoon cuniculi is probably the most extensively studied mammalian microsporidian and has been reported to infect a wide range of hosts, including common laboratory rodents as well as human and non-human primates. This is the first microsporidian species infecting humans that has been considered a zoonosis (Deplazes et al. 1996, Didier et al. 1996) .
The first identification of E. intestinalis in mammals other than humans was reported by Bornay et al. (1998) in the faeces of donkeys, dogs, pigs, cow, and goat suggesting that E. intestinalis might also be of zoonotic origin.
Enterocytozoon bieneusi is the most frequent microsporidian found in humans, especially in Aids patients. It has been associated mainly with chronic diarrhoea, although it has been diagnosed in patients with other forms of immunosuppression and in immunocompetent travellers with self-limited diarrhoea (Weber & Bryan 1994, Sobottka et al. 1995). In addition, this pathogen has recently been detected in other natural hosts such as pigs (Deplazes et al. 1996, Breitenmoser et al. 1999, Rinder et al. 2000), cows, goats, pigs, chickens, cats, turkeys (Bornay et al. 1998), rabbits, dogs (del Aguila et al. 1999), and in simian immunodeficiency virus-inoculated monkeys (Tzipori et al. 1997, Mansfield et al. 1997). Consequently, this microsporidian infection may be more common than previously suspected.