There are over 150 known Sarcocystis species, and at least one is capable of infecting and causing disease in man. Extraintestinal (muscular) sarcocystosis and intestinal sarcocystosis are the two known manifestations of disease in humans. In this series of six cases and review, we focus on the invasive extraintestinal ("muscular") form of sarcocystosis in humans. This disease, which until recently was rarely described, has become relevant particularly as an imported condition in travelers due to a recent series of outbreaks reported from Malaysia. Human intestinal sarcocystosis is ubiquitous across the globe. However, absolute numbers of probable and particularly confirmed cases are few, with only several hundred described to date. Characteristically, patients exhibit signs and symptoms either 1-2 weeks after exposure, or after 4-8 weeks. Whether people remain asymptomatic or develop disease apparently depends on the infecting species, host factors, and the inoculum size. The definitive host(s) remain uncertain, and identification of the animal reservoir(s) requires further research. A better understanding of the epidemiology of the disease, as well as its immunological determinants, is hampered by the lack of reliable serological diagnostic methods. Additionally, DNA seems to be contained very effectively within the encysted parasite, thereby rendering PCR detection unreliable. Physicians should suspect the condition in patients with suggestive symptoms and a possible history of exposure. Surveillance networks for imported infectious diseases are formidable tools to help detect and localize outbreaks.
Nipah virus is an emerging zoonotic pathogen that causes severe febrile encephalitis resulting in death in 40% to 75% of human cases. Nipah virus is considered a biosafety level-4 pathogen and is listed as a select agent with high risk for public health and security due to its high mortality rate in people and the lack of effective vaccines or therapies. The natural reservoir for Nipah virus and related members of the genus Henipavirus are fruit bats of the genus Pteropus. Nipah virus emerged in Malaysia in 1998 as a porcine neurologic and respiratory disease that spread to humans who had contact with live, infected pigs. Research reviewed in this paper suggests that anthropogenic factors, including agricultural expansion and intensification, were the underlying causes of its emergence. Nipah virus has caused five subsequent outbreaks between 2001 and 2005 in Bangladesh. Here, it appears to have spilled over directly from bats to humans, and person-to-person transmission is evident suggesting a heightened public health risk.
Nipah virus was first discovered in 1999, after a severe outbreak of viral encephalitis among pig farm workers in Malaysia. The disease is thought to spread from Pteropus bats to pigs and then to humans following close contact. The reported mortality rate in this outbreak was 40%. The main necropsy finding in patients with Nipah virus encephalitis was disseminated microinfarction associated with vasculitis and direct neuronal involvement. Relapse of encephalitis was seen in 10% of those who survived the initial illness. Since that initial report, recurrent outbreaks of Nipah virus encephalitis have been seen in Bangladesh and West Bengal, India. These outbreaks occurred between January and May, with Pteropus giganteus as a reservoir of the virus. In Bangladesh, the virus probably spread directly from bats to humans-with human to human spread as another important mode of infection-and the mortality rate was 70%.