A comparative study of infections with rodent isolates of Giardia duodenalis in inbred strains of rats and mice and in hypothymic nude rats.

Giardia isolated from mice and rats have been identified as Giardia duodenalis by morphological criteria. No differences in the electrophoretic mobilities of 28 enzymes were detected between the mouse and rat isolates or between these isolates and human and cat isolates. Infections with both rodent isolates have been studied in several strains of inbred rats. No significant differences were detected between the rat strains, with the mouse isolate producing a self-limiting infection and the rat isolate a chronic infection. After the primary infection was eradicated with metronidazole, all strains of rats were resistant to reinfection with the homologous isolate. Both isolates produced chronic infections in hypothymic nude rats. BALB/c mice were found to be relatively resistant to primary infection with either isolate but C3H mice became infected chronically with the mouse isolate and experienced a prolonged infection with the rat isolate. These findings resemble those observed with infections with G. muris in the same strains of mice (Roberts-Thomson & Mitchell 1978). It is suggested that infections with G. duodenalis in rats may offer a model for giardiasis that is based on organisms related closely to G. lamblia. Comparative studies using the two rodent isolates may lead to a better understanding of how the parasite establishes as a chronic infection and which antigens induce protective immune responses.

Biliary antibody response in rats infected with rodent Giardia duodenalis isolates.

Using a sensitive ELISA, specific serum and bile anti-Giardia IgM and IgA responses were studied in rats infected with two strains of Giardia duodenalis: a rat isolate which produces a chronic infection and a mouse isolate which produces a self-limiting infection. Paired samples of serum and bile were collected from groups of DA (RT1avl) rats at various times during primary and secondary infections. Antibody responses to both organisms were similar. Only IgA anti-Giardia antibodies were detected in bile whereas both IgM and IgA antibodies were detected in serum. Biliary IgA antibody titres increased throughout the course of the primary infection and remained at high levels for at least 10 weeks. Biliary IgA titres increased 16-fold during the secondary infection with both isolates. Serum IgA anti-Giardia titres also increased but more slowly than the titres in bile. Serum IgM antibody responses were observed against both organisms during the primary and secondary infections. Trophozoites harvested from the intestinal lumen during primary infections were examined for surface-bound IgA by immunofluorescence microscopy. IgA was detected on 3% of trophozoites on day 7 after infection but on over 70% of trophozoites by the 10th day. The data demonstrate the occurrence of a secretory IgA immune response in rats infected with both G. duodenalis isolates, some of which is directed against surface antigens of the trophozoites.

Prevention of pneumococcal infection in children with homozygous sickle cell disease.

The efficacy of prophylactic penicillin and of 14 valent pneumococcal vaccine in preventing pneumococcal infection in homozygous sickle cell (SS) disease was investigated in 242 children aged 6 months to 3 years at entry. In the first five years of the trial there were 11 pneumococcal infections in the pneumococcal vaccine treated group, 10 by serotypes present in the vaccine. Type 23 accounted for five of these, and there was evidence of higher infection rates in those given the vaccine before age 1. No pneumococcal isolations occurred in the penicillin group while receiving penicillin, although four isolations occurred within one year of stopping penicillin. Probably the most effective prophylaxis against pneumococcal infection requires penicillin beyond the age of 3. The age at which pneumococcal vaccine should be given must await further data on antibody response and clinical efficacy in these patients.