Читать книгу Parasitology - Alan Gunn - Страница 94

Humans are the definitive hosts for S. bovihominis, S. suihominis and several other species of Sarcocystis that we usually acquire from eating raw or poorly cooked meat. As definitive hosts to these parasites, we suffer from intestinal infections. The symptoms are non‐specific and typically include nausea and diarrhoea. The infections are usually self‐limiting and seldom serious.

We can also act as intermediate hosts for some Sarcocystis species. For example, we can act as an intermediate host for Sarcocystis nesbitti although in most cases the species responsible is uncertain. The definitive hosts for S. nesbitti are probably snakes or other reptiles. Therefore, in common with the other species for which we are intermediate hosts, we are ‘dead end’ hosts because few animals have the opportunity to eat us. Presumably, we suffer accidental infections with the sporocysts/oocysts through contamination of food or water and the normal intermediate hosts are other species of primates. The symptoms of infection depend upon the site at which the sarcocysts grow and their abundance. Typically, they induce inflammatory responses that result in pain, fever, and swelling at the infected site. There are reports of regular outbreaks of human sarcocystosis amongst tourists visiting parts of Malaysia (Fayer et al. 2015). Whether these link to one or more species of Sarcocystis is uncertain.

In intermediate hosts, the consequences of infection vary between species, the level of challenge, and the species of Sarcocystis parasitizing them. However, most pathology is usually associated with damage caused to the vascular epithelium during the second stage of merogony. Heavy infections of S. bovicanis in cattle can result in widespread haemorrhages afflicting virtually every organ in the body. This results in anaemia, emaciation, and the animal may become anorexic; abortion can occur in breeding cattle. The immune response results in lymphadenopathy and submandibular oedema whilst the hair at the end of the tail is often lost. Most infections in domestic livestock, however, are subclinical and not discovered until the sarcocysts are detected during meat hygiene inspections after the animal is slaughtered.