No abstract

No abstract

The human and animal pathogen Giardia lamblia is a waterborne risk to public health because the cysts are ubiquitous and persistent in water and wastewater, not completely removed by physical-chemical treatment processes, and relatively resistant to chemical disinfection. Given the recently recognized efficacy of UV irradiation against Cryptosporidium parvum oocysts, the inactivation of G. lamblia cysts in buffered saline water at pH 7.3 and room temperature by near monochromatic (254 nm) UV irradiation from low-pressure mercury vapor lamps was determined using a "collimated beam" exposure system. Reduction of G. lamblia infectivity for gerbils was very rapid and extensive, reaching a detection limit of >4 log within a dose of 10 JM-2. The ability of UV-irradiated G. lamblia cysts to repair UV-induced damage following typical drinking water and wastewater doses of 160 and 400 JM(-2) was also investigated using experimental protocols typical for bacterial and eucaryotic DNA repair under both light and dark conditions. The infectivity reduction of G. lamblia cysts at these UV doses remained unchanged after exposure to repair conditions. Therefore, no phenotypic evidence of either light or dark repair of DNA damage caused by LP UV irradiation of cysts was observed at the UV doses tested. We conclude that UV disinfection at practical doses achieves appreciable (much greater than 4 log) inactivation of G. lamblia cysts in water with no evidence of DNA repair leading to infectivity reactivation.

Mongolian gerbils were susceptible to infection with Giardia lamblia cysts from patients. Inoculation of gerbils with 5 x 10(3) cysts each resulted in an infection characterized by the intermittent release of cysts for up to 39 days. The mean number of cysts released per gerbil in a 2-hr period was 8.8 x 10(2) (range, 0-5 x 10(3)). The highest number of trophozoites found in the intestine was on day 15 after infection, when the mean number of trophozoites per gerbil was 6.36 x 10(6). Administration of cysts from different patients to gerbils resulted in a similar pattern of cyst release during the first 30 days of infection. Mongolian gerbils were also susceptible to infection with cultured trophozoites (Portland 1 strain). The pattern of cyst release and the number of trophozoites in the intestines of orally and duodenally inoculated gerbils were similar. Gerbils were protected against reinfection with G. lamblia for up to eight months after primary infection.

SUMMARY The intestinal protozoan Giardia duodenalis is a widespread opportunistic parasite of humans and animals. This parasite inhabits the upper part of the small intestine and has a direct life cycle. After ingestion of cysts, which are the infective stage, the trophozoites emerge from the cysts in the duodenum and attach to the small intestinal mucosa of the host. Since the migration of trophozoites from the lumen of the intestine into surrounding tissues is an unusual occurrence, the immune response to Giardia remains localized. The identification of antigens that play a role in acquired immunity has been difficult because of the occurrence of antigenic variation and because, Giardia being an ubiquituous organism, it is possible that the antigenic profiles of isolates from different geographic areas will vary. Innate-immunity mechanisms play a role in the control and/or severity of the infection. Both humoral and cell-mediated immune responses play a role in acquired immunity, but the mechanisms involved are unknown. A variety of serological assays have been used to detect circulating antibodies in serum. Because of the biological characteristics of the parasite and the lack of suitable antigens, the sensitivity of serological assays remains poor. On the other hand, detection of antigens in feces of infected patients has met with success. Commercial kits are available, and they are reported to be more sensitive than microscopic examination for the detection of giardiasis on a single specimen.

No abstract

The process of encystation is a key step in the Giardia duodenalis life cycle that allows this intestinal protozoan to survive between hosts during person-to-person, animal-to-person, waterborne, or food-borne transmission. The release of cysts from infected persons and animals is the main contributing factor to contamination of the environment. Genes coding for cyst wall proteins (CWPs), which could be used for developing a transmission-blocking vaccine, have been cloned. Since the immunogenicity of recombinant Giardia CWP is unknown, we have investigated the immunogenicity of recombinant CWP2 (rCWP2) and its efficacy in interfering with the phenomenon of encystation taking place in the small bowels of BALB/c mice vaccinated with the recombinant protein. Here we report that the immunization of BALB/c mice with rCWP2 stimulated the immune system in a manner comparable to that for a live infection with Giardia muris cysts. Fecal and serum anti-rCWP2 immunoglobulin A (IgA) antibodies were detected in the immunized mice. In addition, anti-rCWP2 IgG1 and IgG2a antibodies were detected in the serum. mRNAs coding for Th1 and Th2 types of cytokines were detected in spleen and Peyer's patch cells from immunized mice. When the vaccinated mice were challenged with live cysts, the animals shed fewer cysts. We conclude that rCWP2 is a possible candidate antigen for the development of a transmission-blocking vaccine.

SUMMARY The sequence of changes in the activity of six disaccharidases in the small intestine of gerbils during primary and secondary G lamblia infections was examined. The primary G lamblia infection induced a transient reduction in disaccharidase activity which was related to the highest trophozoite burden in the small intestine. During the primary exposure, a 30% to 85% decrease in the activity of enzymes was observed on days 10 and 20 after infection. Secondary exposure of gerbils to G lamblia caused a sharp decrease in disaccharidase activity as early as 24 h after challenge. The reduction in the enzyme activity was not influenced by the size of the challenge inoculum and occurred even when there were no live trophozoites in the small intestine. Disaccharidase deficiency could also be induced by challenge with the soluble extract of the trophozoites. Multiple challenge administrations of G lamblia trophozoites to gerbils induced a persistent disaccharidase deficiency. The results indicate that disaccharidase deficiency associated with the primary G lamblia infection probably represents a direct effect of the parasite on the brush border of the small intestine. On the other hand, the observed disaccharidase deficiency in the secondary G lamblia infection appears to be induced by the local immune responses of the host.Various abnormalities of small bowel pathology have been identified consistently in human giardiasis and these include disaccharidase deficiencies,' 2 increased intraepithelial lymphocyte counts'4 and, in patients with malabsorption crypt hyperplasia with short villi and increased lamina propria cellularity.) Low serum calcium and folate concentrations were consistent features in elderly people having giardiasis and aroused suspicion of underlying malabsorption." A decrease in the disaccharidase activity has been observed in vitro. Mouse mucosal cells incubated with G lamblia trophozoites showed a reduction in the activities of lactase, sucrase, and maltase.7We have recently described an animal model for giardiasis using gerbils and G lamblia isolated from humans.' In this study, we examined the progression