The passive transfer of convalescent sera did not protect the majority of mice against challenge with the homologous strain and was completely ineffective against challenge with strains unrelated by fluorescent antibody techniques. When the immune sera was incubated with the rickettsia in vitro and then inoculated into the mice a dramatic increase occurred in the number of surviving mice. The importance of these data in relation to published results with other species of rickettsia is discussed.
This study aimed to describe the transmission dynamics, the serological and virus excretion patterns of Nipah virus (NiV) in Pteropus vampyrus bats. Bats in captivity were sampled every 7-21 days over a 1-year period. The data revealed five NiV serological patterns categorized as high and low positives, waning, decreasing and increasing, and negative in these individuals. The findings strongly suggest that NiV circulates in wild bat populations and that antibody could be maintained for long periods. The study also found that pup and juvenile bats from seropositive dams tested seropositive, indicating that maternal antibodies against NiV are transmitted passively, and in this study population may last up to 14 months. NiV was isolated from the urine of one bat, and within a few weeks, two other seronegative bats seroconverted. Based on the temporal cluster of seroconversion, we strongly believe that the NiV isolated was recrudesced and then transmitted horizontally between bats during the study period.
The lymphatic filarial parasites which affect about 90 million people worldwide have similar host-parasite relationships in man. They are all able to survive, reproduce and cause chronic infections if they can successfully evade the protective responses of the host. Studies to investigate the wide spectrum of clinical manifestations of the infection even among those living in similar endemic areas and with presumed equal exposure to infective larvae, have been hampered by the lack of animal models showing similar host-parasite responses. The recent use of the nude mouse infected with Brugia spp, and the leaf-monkey (Presbytis spp) infected with B. malayi or Wuchereria spp for the study of immune responses and the associated pathology of these infections, has elucidated some of the host protective immune responses as well as the associated immunopathological reactions. The successfully entrenched parasite elicits minimal reactions and pathology, but with the onset of effective host responses, whether assisted by chemotherapy, development of protective immunity or both, severe inflammatory responses may occur. The role of such immune mediated response in determining subsequent pathology will probably be dependent on the frequency and duration of these episodes, but these have yet to be defined. Prenatal and perinatal sensitization by filarial antigens are postulated to result in tolerance and/or modification of immune responses to subsequent infections. A role for genetic predisposition to certain clinical outcomes, for example, the development of elephantiasis, has been postulated but needs further study. Advances have also been achieved in defining those parasite antigens/products involved in eliciting or suppressing protective and other immune responses.(ABSTRACT TRUNCATED AT 250 WORDS)