Arthropod-borne apicomplexan pathogens that cause asymptomatic persistent infections present a significant challenge due to their life-long transmission potential. Although anti-microbials have been used to ameliorate acute disease in animals and humans, chemotherapeutic efficacy for apicomplexan pathogen elimination from a persistently infected host and removal of transmission risk is largely unconfirmed. The recent re-emergence of the apicomplexan Theileria equi in U.S. horses prompted testing whether imidocarb dipropionate was able to eliminate T. equi from naturally infected horses and remove transmission risk. Following imidocarb treatment, levels of T. equi declined from a mean of 104.9 organisms/ml of blood to undetectable by nested PCR in 24 of 25 naturally infected horses. Further, blood transfer from treated horses that became nested PCR negative failed to transmit to naïve splenectomized horses. Although these results were consistent with elimination of infection in 24 of 25 horses, T. equi-specific antibodies persisted in the majority of imidocarb treated horses. Imidocarb treatment was unsuccessful in one horse which remained infected as measured by nested PCR and retained the ability to infect a naïve recipient via intravenous blood transfer. However, a second round of treatment eliminated T. equi infection. These results support the utility of imidocarb chemotherapy for assistance in the control and eradication of this tick-borne pathogen. Successful imidocarb dipropionate treatment of persistently infected horses provides a tool to aid the global equine industry by removing transmission risk associated with infection and facilitating international movement of equids between endemic and non-endemic regions.

Fimbrial vaccines are routinely given parenterally to pregnant cattle, sheep and swine to protect suckling newborn calves, lambs and pigs against enterotoxigenic Escherichia coli (ETEC) infections. Such vaccines are practical and effective because (1) most fatal ETEC infections in farm animals occur in the early neonatal period when the antibody titres in colostrum and milk are highest; (2) more than 90% of the ETEC in farm animals belong to a small family of fimbrial antigen types; (3) fimbriae consist of good protein antigens on the bacterial surface where they are readily accessible to antibody; (4) fimbriae are required for a critical step (adhesion-colonization) early in the pathogenesis of the disease. ETEC infections continue to be a significant clinical problem in farm animals in spite of extensive use of fimbriae-based vaccines. Definitive data on the efficacy of the commercial vaccines in field use are not available. The prevailing perception among animal health professionals is that the vaccines are effective, that the problem occurs chiefly among non-vaccinated animals, and that in some herds vaccination moves peak prevalence of disease from the first to the second or third week after birth, when mortality is lower. It has been suggested that extensive use of vaccines will rapidly select for the emergence of novel or previously low prevalence fimbrial antigen types. There is no evidence that this has happened after a decade of routine vaccine use in the United States. However, there is no active direct surveillance for such emergence.(ABSTRACT TRUNCATED AT 250 WORDS)

No abstract

SUMMARYThe antigenic relatedness of minute virus of mice (MVM), Kilham rat virus (KR), H-1 virus (H-1), haemorrhagic encephalopathy of rats virus (HER), porcine parvovirus (PPV), canine parvovirus (CPV), feline panleukopenia virus (FPV), goose parvovirus (GPV) and bovine parvovirus (BPV) was studied by immunofluorescence microscopy (FA) and by serum neutralization (SN). An antigenically related group comprising MVM, KR, HER, PPV, CPV and FPV was recognized by FA and most reactions within the group were reciprocal. Antigenic relatedness was less evident when the same viruses and antisera were tested by SN. Only CPV and FPV were closely and reciprocally related. Other cross-reactions by SN were quantitatively minor and included neutralization of CPV and FPV by pig anti-PPV serum and neutralization of H-1 and HER by rat anti-KR serum. Neither FA nor SN revealed any antigenic relationship of BPV and GPV either with each other or with any of the other viruses tested.