An immunocompetent rat model of infection with Cryptosporidium hominis and Cryptosporidium parvum.

A major obstacle to developing vaccines against cryptosporidiosis, a serious diarrheal disease of children in developing countries, is the lack of rodent models essential to identify and screen protective immunogens. Rodent models commonly used for drug discovery are unsuitable for vaccine development because they either are purposefully immunodeficient or immunosuppressed. Here, we describe the development and optimization of an immunocompetent intratracheal (IT) rat model susceptible to infections with sporozoites of Cryptosporidium parvum and Cryptosporidium hominis - the primary causes of human cryptosporidiosis. A model suitable for screening of parasite immunogens is a prerequisite for immunogen screening and vaccine development.

Effects of age and splenectomy on heavy infection of Angiostrongylus cantonensis in rats.

This study was designed to determine the effects of age and the role of spleen in rats with heavy Angiostrongylus cantonensis infection. Young rats (8 weeks) infected with 100 larvae were found to have significantly higher worm recovery rate (75.0±6.6%) than the adult (6 months) (55.7±1.5%) and the aging ones (13 months) (57.6±4.0%). Moreover, the recovery rate in adult rats with 400 larvae (33.6±10.67%) was significantly lower than those with 100 larvae (55.7±1.53%) or 200 larvae (53.3±5.4%). The splenectomized young rats with 100 larvae had a significantly higher recovery rate (84.3±2.5%) than the intact (75.0±6.6%) or sham splenectomized ones (74.4±3.8%). Although titers of antibody against A. cantonensis increased with time, those against young adults were significantly higher before week 4 whereas those against adult worms become significantly higher since week 4. Titers in the splenectomized rats were also found to be significantly lower than those in the intact ones. These finding indicate that young rats are more susceptible to A. cantonensis. Crowding effect may occur in rats with heavy infections. The effects of splenectomy on the host are independent of the intensity of infection.

The acute effects of single-dose orally administered doramectin, eprinomectin and selamectin on natural infections of Syphacia muris in rats.

This study was designed to determine the acute effects of a single-dose of orally administered doramectin, eprinomectin and selamectin on Syphacia muris infection in rats. Rats, naturally infected with S. muris, were divided into four groups: three different treatment groups (n=7) and one positive control (n=7). Cellophane tape preparations were obtained from the treated rats on day 0 pre-treatment and on days 2, 4 and 6 post-treatment. Syphacia sp. eggs were counted. Eprinomectin was found to be 100% effective in eliminating eggs on two post-treatment. However when egg counts on day 6 post-treatment were compared with pre-treatment egg counts, doramectin and selamectin were found to be 99.32 and 98.77% effective in eliminating eggs, respectively. On day 7 post-treatment, blood samples were obtained from all groups, and then the rats were necropsied. Doramectin, eprinomectin and selamectin were found to be 100% effective in eliminating adult S. muris, when compared with the positive control group.

Fenbendazole treatment and litter size in rats.

Fenbendazole is commonly used in laboratory animal medicine as an anthelmintic for elimination of pinworms. It is generally regarded as a safe drug with minimal side effects. In our facility, 2 breeding colonies of rats were treated with fenbendazole to eliminate pinworms. Analysis of the breeding records revealed that feeding Sprague-Dawley rats a diet containing fenbendazole on a continuous basis for 7 consecutive weeks was associated with a significant reduction in litter size. Although the mechanism underlying this effect is unknown, the finding prompts caution when using fenbendazole to treat valuable breeding colonies or strains that are poor breeders.

Preference of female rats for the odours of non-parasitised males: the smell of good genes?

Many animals obtain reliable information about potential mates, including whether they are parasitised or not, mostly from olfactory cues in urine. Previous experiments with rodents have shown that females can detect parasites in males that are potentially transmissible during copulation, so that females can directly avoid infection by discriminating against parasitised males. Here, using choice tests, we examine whether female rats can distinguish males infected with the tapeworm Hymenolepis diminuta Rudolphi, 1819, a parasite with a complex life cycle and thus not directly transmissible among rats. Female rats tended to spend more time investigating the urine of non-parasitised males than that of parasitised males. The magnitude of the parasite burden in the infected males had no effect on the females' preference for the non-parasitised males. We also found that parasitised males had lover testosterone levels in their blood than non-parasitised males. These results suggest that females use cues in male urine reflecting either the presence of the parasite and/or lower testosterone levels to avoid parasitised males and possibly secure resistance genes for their offspring.

IgG isotype specific immune response in rats infected with Fasciola hepatica.

Antibody responses (IgG1, IgG2a, IgG2b, and IgG2c subclasses) against Fasciola hepatica L. in rats infected with metacercariae were analysed by ELISA. Animals of group 1 (R-1) remained infected throughout 21 weeks, and rats of group 2 (R-2) received a single oral dose of triclabendazole (Fasinex 10%, Ciba-Geigy) at 4 weeks after infection. Group C (R-C) consisted of rats left intact which served as uninfected controls. All IgG subclasses increased during the first weeks after infection, but when triclabendazole was administered IgG1 and IgG2b diminished markedly. IgG2c showed a different profile to the other antibodies evaluated, increasing earliest and decreasing profoundly from the 9-11th week after infection (w.a.i). The infected-untreated rats produced higher titres of antibodies than the rats of R-2, and these differences were statistically significant (p < 0.05) in all subclasses evaluated except in IgG2a titres.

Plagiorchis muris: recovery, growth and development in albino rats.

Metacercariae of Plagiorchis muris, obtained from naturally infected dragonflies, Sympetrum eroticum, successfully established in 4-week-old albino rats up to 14 days post-infection (p.i.) but by day 28 p.i. the recovery rate had significantly decreased. The genital primordia in excysted metacercariae were differentiated into those of metraterm, Mehlis' gland, ovary and cirrus pouch, with the primordial testes appearing on day 1 p.i. The vitellaria and eggs in the uterus were present in flukes on days 2 and 4 p.i., respectively. Mature flukes were established in the lower part of the small intestine on day 5 p.i., with the peak of egg production occurring on day 14 p.i. Growth of the flukes continued up to day 28 p.i.

Comparative infectivity of Toxoplasma gondii bradyzoites in rats and mice.

Infectivity of Toxoplasma gondii bradyzoites was compared in outbred female Sprague Dawley rats and outbred Swiss Webster mice. Rats inoculated subcutaneously with 1-10 bradyzoites of the 2 strains of T. gondii (VEG and GT-1) developed persistent infection, whereas an infective dose by the oral route was 10-1,000 bradyzoites. The infectivity of bradyzoites of the VEG and the GT-1 strains of T. gondii in rats by the subcutaneous route was comparable to that in mice.

Preliminary biochemical characterization of faeces from uninfected rats and rats infected with the tapeworm, Hymenolepis diminuta.

Faecal pellets were collected from uninfected rats and rats infected with Hymenolepis diminuta, and analysed for caloric value, lipids, carbohydrates, glucose, amino acids, and proteins. Faeces from infected rats contained significantly more lipid and less carbohydrate and glucose than faeces from control rats. The total free amino acid content of faeces from infected and control rats did not differ, but there were significant differences in the amounts of individual free amino acids. The data support the hypothesis that the nutrient composition of faeces from infected and control hosts differ. Beetles that serve as the intermediate host for H. diminuta may be able to detect these differences, and this may explain why beetles preferentially ingest faeces containing the tapeworm s eggs.

Pathogenicity and infectivity of Toxoplasma gondii oocysts for rats.

Rats are considered to be 1 of the most resistant hosts for Toxoplasma gondii infection, but relative infectivity of T. gondii for rats is not known. Therefore, infectivity and pathogenicity of oocysts of the VEG strain of T. gondii were studied in Sprague Dawley weaned rats (approximately 130 g). Groups of 5 rats were each inoculated orally with 1 to 1 million infective oocysts. Three of the 5 rats fed 1 million oocysts died of acute toxoplasmosis between 6 and 9 days after ingesting oocysts; all other rats survived. Tissue cysts were found in brains of all rats fed > or = 10 oocysts and in 3 of 6 rats fed 1 oocyst. The average number of tissue cysts in brains of rats was 300, 180, 528, 600, 396, 1,200, and 2,650 in rats fed 1, 10, 100, 1,000, 10,000, 100,000 or 1 million oocysts, respectively. Microscopic lesions were seen in brains of all T. gondii-infected rats and the frequency of lesions was usually proportional to the dose. Antibodies (> or = 1:512) to T. gondii were detected in sera of all infected rats 29 days after ingestion of oocysts by the modified agglutination test, the commercially available latex agglutination test, and the indirect hemagglutination test.

Studies on host specificity in Paragonimus westermani: ultrastructural study of inflammatory reactions to the parasite in rat muscles.

Inflammatory reactions to the lung fluke, Paragonimus westermani, in an abnormal host, the rat, were studied by electron microscopy. Inflammatory cells accumulated around the worms in rat muscles, but the reaction varied significantly in intensity as well as distribution of inflammatory cells from worm to worm in the same and different hosts. In an accumulation of inflammatory infiltrates around the worm, eosinophils were more commonly seen, and neutrophils and macrophages were fewer in number. Mast cells appeared rarely. Where inflammatory cells touched to the worms, the tegument of the worms was covered with moderately electron-dense flocculent material which included dense granules. This material, which probably consisted of immune complexes of host antibody and antigen secreted from tegumental granules, seemed to block the inflammatory cells from adhering to the worm surfaces. Inflammatory cells made direct contact with worm surfaces where flocculent material was absent. Dense secretory material was discharged from some eosinophils as a result of degranulation.

An alternative protocol for the serial passage and maintenance of a homogonic strain of Strongyloides ratti in female Sprague-Dawley rats.

A method which does not involve the tedious use of watch glass coprocultures for obtaining filariform infective (L3) larvae of Strongyloides ratti from faecal pellets of infected Sprague-Dawley rats is described. The alternative method utilises Baermannization (18 h) of faecal pellets to yield rhabditiform (L1) larvae of S. ratti and their subsequent culture for 72 h at 19 degrees C in tissue-culture-flasks containing only dechlorinated tap water to yield infective filariform (L3) larvae. The yields and infectivity of the L3 larvae obtained from the two methods were essentially similar.