Schistosoma Sp

Schistosoma sp Schistosoma sp. (schistosomiasis, Cacing darah) Karolinska Institute Medis Gambar, 2001 Siklus hidup dari tiga spesies utama schistosomes manusia serupa. Laki-laki dan perempuan cacing ratarata sekitar 10 mm dan hidup dalam pembuluh darah dari rongga perut. Di sini mereka kawin dan betina menghasilkan telur. Cacing dewasa dapat hidup 20-30 tahun dan, tergantung pada spesies, dan perempuan masing-masing dapat menghasilkan beberapa ratus telur setiap hari. Telur melarikan diri dari tubuh dengan menembus dinding pembuluh darah dan usus kecil atau kandung kemih, dan mereka lulus dalam tinja atau urin. Telur menetas dalam air, hospes perantara pertama (siput) terinfeksi, dan kulit mereka dan mereka menjadi terinfeksi. Hal ini terjadi ketika manusia berenang, mandi, mencuci pakaian, dll, di sungai dan sungai. Setelah serkaria menembus kulit cacing dewasa masuk ke dalam sistem peredaran darah dan bermigrasi ke pembuluh darah rongga perut, dan dalam waktu sekitar enam minggu mereka mencapai seksual Sebagai telur dari schistosomes menembus dinding pembuluh darah dan usus kecil atau kandung kemih, mereka menyebabkan sejumlah besar kerusakan pada jaringan. Perdarahan jaringan, sehingga darah sering muncul dalam urin atau feses. Sebagai infeksi berlangsung jaringan menjadi meradang dan fibrosis dan tidak mampu berfungsi secara normal. Banyak dari telur yang dihasilkan oleh cacing betina tidak melarikan diri dari pembuluh darah, tetapi menyapu dalam sistem peredaran darah dan disimpan di hati tuan rumah. Hati menanggapi kehadiran telur oleh encapsulating mereka dalam granuloma berserat. Kerusakan pada usus kecil (atau kandung kemih) dan hati terakumulasi dari waktu ke waktu dan mengakibatkan kronik, melumpuhkan penyakit yang dapat berakibat fatal. Seperti infeksi trematoda sebagian, diagnosis yang paling sering tergantung pada menemukan telur parasit. Dalam kasus S. haematobium, telur yang paling sering ditemukan dalam urin, telur dari dua spesies lainnya yang paling sering ditemukan dalam feses

Strongyloides sp. parasitic nematodes with a facultative free-living generation Introduction The nematode genus Strongyloides consists of parasites that live as parthenogenetic females in the small intestines of their vertebrate hosts. In addition to producing parasitic offspring, Strongyloides spp. can also form a facultative free-living generation with males and females. A generalized life cycle of Strongyloides sp. is shown in Figure 1. For a general introduction into the biology of Strongyloides sp. by

Mark E. Viney and

James B. Lok

click here. We work

mainly with S. papillosus, a common parasite of sheep and goats, which can be raised in rabbits and S. ratti, a parasite of rats.

Figure 1: Left: Life cycle of Strongyloides papillosus (from Nemetschke et al., 2010). Right: DIC micrographs of parasitic (top, photo: L. Nemetschke) and free-living (bottom) S. papillosus adults (from Streit, 2008).

Genetics Classical genetic approaches are rarely used with metazoan endo-parasites, largely because the adult stages are usually hidden within hosts, making controlled crosses difficult. The existence of a free-living generation inStrongyloides spp. offers a remarkable opportunity for the experimental manipulation of a parasite. We would like to explore this opportunity and conduct genetic screens in Strongyloides spp. We established a genetic linkage map for S. ratti (in collaboration with

Mark

Viney, University of Bristol) and we are analyzing and comparing the inheritance and linkage of molecular genetic markers in S. ratti and in S. papillosus. We are

particularly interested in differences between the two species, which relate to their different sex determining systems.

Sex determination and sex chromosomes Interestingly, the sex determining mechanisms vary within the genus Strongyloides. There are species with true sex chromosomes such that individuals with two X chromosomes (plus two pairs of autosomes) are female and individuals with one X are male. Other species, for example S. papillosus have only two pairs of chromosomes, one of which is considerably larger than the other. Already more than 30 years ago it was speculated that this is the result of a fusion of the X chromosome with one of the autosomes. In old, cytological studies some authors found no chromosomal differences between the sexes of S. papillosus. Others described that in males a portion of one chromosome is eliminated, thereby creating a hemizygous region (sex specific chromatin diminution). Recently, by combining cytological and molecular genetic approaches, we demonstrated that in S. papillosus males an internal portion of one of the two larger chromosomes is eliminated. Further we showed that the region undergoing chromatin diminution contains a high number of genes and is homologous to the X chromosome of S. ratti. The portions of the longer chromosome that is not diminished corresponds to chromosome number I of S. ratti. These findings strongly support the chromosome fusion hypothesis. Further we observed that males do not pass on their diminished chromosome to their progeny. This results in a male specific transmission ratio distortion for genetic loci closely linked with the diminished region.