EMC - Maladies Infectieuses最新文献

Microsporidia and Isospora and Sarcocystis coccidia are unicellular parasites responsible for enteric infections in humans. The development of these parasites is intracellular. Microsporidia and Isospora infect predominantly immunocompromised patients. Severe clinical manifestations result from the dissemination of the infection in the absence of cellular immune response. Intestinal microsporidiosis, an infection unknown before AIDS pandemia, was the prevalent cause of diarrhoea in HIV infected patients from industrial countries, before the introduction of highly active antiretroviral therapies. Apparently HIV infection did not increase the incidence of Sarcocystosis. Microsporidiosis and isosporosis are still reported in countries where AIDS pandemia remains uncontrolled. Recent epidemiological data indicate the occurrence of a wide reservoir of animal hosts for microsporidia causing intestinal infections in humans. Man is the unique reservoir for Isospora belli, the species responsible for human isosporosis. One animal host (pig or bovine) is reported for the two Sarcocystis species which complete their development in the human. Different methods are available for the detection of these pathogens in patients, human and animal hosts and the environment.

HHV-8 belongs to the herpesviridae family, to the gammaherpesvirinae sub-family and to the rhadinovirus genus. While several viral homologues exist in different types of non human primates, HHV-8 is the only rhadinovirus known in human. The HHV-8 genome comprises a unique long region of 140 kb, containing nearly 90 genes, with, at both extremities, terminal repeated regions that comprise identical repeated sequences in variable number. Among these genes, some encode proteins necessary for the viral replication and the assembly of new particles (structural proteins, DNA polymerase, glycoproteins), others in contrast, encode homologues of cellular protein involved in the regulation of the cell cycle, apoptotic cell death mechanisms and cellular proliferation. HHV-8 has indeed several genes which have been hijacked from the host during a long parallel evolution. These viral genes, divergent homologues of the original cellular genes, play a crucial role in the tumorigenesis mediated by HHV-8 but also in mechanisms leading to escape the anti viral immune response. HHV-8 is considered as the etiological agent of the four clinico-epidemiologic forms of Kaposi's sarcoma (classic, endemic, post-transplant and epidemic/HIV associated). This human oncogenic herpesvirus is also associated with primary effusion lymphoma and some cases of multicentric Castleman disease as well as other rare lymphomas. HHV-8 is not a ubiquitous virus. It is principally endemic in areas of high endemicity for classic or endemic Kaposi's sarcoma including the Mediterranean zone, and mostly East and Central Africa. In the latter areas, HHV-8 seroprevalence can reach 80% among the adult population. While in the HHV-8 highly endemic male homosexual population (mainly in the USA and Europe), this herpesvirus is transmitted during repeated sexual contacts, HHV- 8 transmission occurs mainly from mother to child and between siblings in the general population of endemic areas (Africa). Saliva seems to play a major role in the viral transmission, being a possible reservoir for HHV-8. Molecular epidemiological studies of the K1 gene (one of the most variable genomic region) have revealed the presence of different molecular subtypes which appear, at least some of them, mostly linked to the geographical origin of the samples rather than to the associated disease.

The “science of outbreaks” is only a small part of modern epidemiology. An infectious disease is the consequence of interactions between the pathogen, the host, and environmental factors. An epidemiologist has several tasks. Infectious diseases control and prevention rely on cases screening and treatment, individual and collective prophylaxis, vector elimination, and improvement of life conditions and sanitary education. A surveillance system providing continuous reliable data within short time delay is essential for epidemiological surveillance. It has to enable giving alert in case of outbreaks with short delay, and to provide sufficient details on the cases and locations. Outbreak management comes next. Ad hoc field studies are expected to provide details on the circumstances and determinants of the disease. These studies should come out with strategies reducing the outbreak related morbidity and mortality. Epidemiologists are also in charge of assessing the efficacy of preventive and therapeutic strategies.