Immune response to simulated postexposure rabies booster vaccinations in volunteers who received preexposure vaccinations.

Several studies of the efficacy of intradermal postexposure rabies vaccination have shown that this procedure is safe, effective, and cost saving. Less is known about the reliability of the present World Health Organization (WHO)-approved intradermal preexposure regimen, which consists of three 0.1-mL doses that are generally given on days 0, 7, and 28. Previous studies have shown that neutralizing antibody responses are lower and of shorter duration in subjects given the reduced-dose intradermal regimen. Thus, it is still uncertain whether the WHO-recommended single intramuscular or intradermal booster injections given on days 0 and 3 would prevent death in all cases. In this preliminary study, we evaluated titers of neutralizing antibody in Thai student volunteers given two simulated postexposure boosters, as recommended by WHO, and we compared these volunteers to a group given vaccine intramuscularly. We observed a lower, although adequate, accelerated immune response in those given the preexposure series and postexposure boosters intradermally.

Is injection of contaminated animal bite wounds with rabies immune globulin a safe practice?

In Asia, it is still controversial whether it is safe to inject a contaminated animal bite wound with a foreign protein such as equine or human rabies immune globulin, even though this is recommended by the World Health Organization. A prospective study of 114 severe animal bite wounds which were injected with equine or human rabies immune globulin revealed an overall incidence of gross infection of 11.4%. No matched control group of patients bitten by animals whose wounds were not injected with immune globulin could be studied in this environment with a high prevalence of canine rabies. The incidence of wound infection in lacerations inflicted by sharp objects and sutured under local anaesthesia was therefore studied prospectively in 100 Thai patients from a similar socio-economic milieu; it was found to be 13%. Wound infection was more common in animal bites and lacerations of the lower extremities. It is concluded that injecting a properly cleansed bite wound with equine or human rabies immune globulin is a safe practice and should be performed whenever there is a possibility that the biting animal might have rabies.

Postexposure prophylaxis for rabies with antiserum and intradermal vaccination.

The Thai Red Cross intradermal postexposure rabies treatment schedule was prospectively assessed in 100 Thai patients severely bitten by proven rabid animals. It consists of 0.1 ml of purified Vero cell rabies vaccine containing more than 2.5 IU of rabies antigen per 0.5 ml of reconstituted vaccine given intradermally at two sites on days 0, 3, and 7, followed by one 0.1 ml injection on days 30 and 90. The commercial vaccine used had an antigen content of 3.17 IU per 0.5 ml ampoule. Purified equine or human rabies immuno-globulin was also given on day 0 to patients with severe exposures. As much of the immunoglobulin as possible was infiltrated around the wounds. All patients were followed for 1 year post exposure. There were no deaths; the efficacy of the regimen was 100%. Antibody titre determination in a randomly selected subgroup showed seroconversion in all 10 patients.

Failure of rabies postexposure treatment in Thailand.

Three failures of postexposure rabies treatment using imported purified duck embryo cell and Vero cell rabies vaccines are reported from Thailand. Reference is made to eight additional previously reported Thai patients, six of whom had received human diploid cell vaccine. An analysis of these cases reveals that there were serious flaws in management in all of these patients. It is stressed that 45% of human rabies deaths in Thailand occur within 20 days of being bitten and 71% are dead within 28 days. This short incubation period does not allow much time to start immunotherapy. Of Bangkok dogs found to have rabies at autopsy, approximately 8% have a rabies immunization history. Once a dog has bitten a patient immunotherapy should not be delayed in countries with a high incidence of dog rabies. Patients with chronic disease, alcoholics and drug addicts may have an impaired immune response to postexposure rabies vaccines.

Prediction, prevention, and mechanism of early (anaphylactic) antivenom reactions in victims of snake bites.

Victims of snake bites are often subjected to cutaneous or conjunctival hypersensitivity testing before being given antivenom. None of 12 early (anaphylactic) reactions was predicted by these tests in 25 Nigerian and Thai patients. The incidence and severity of early reactions was the same whether antivenom was given by intravenous injection over 10 minutes or diluted and given as an intravenous infusion over 30 minutes. Although antivenom activated complement in vitro, there was no evidence of complement activation or formation of immune complexes in patients bitten by snakes who were treated with antivenom, whether or not they developed early reactions. Higher doses of antivenom might induce the complement activation and formation of immune complexes (aggregates) that have been observed during the clinically more severe reactions associated with homologous immunoglobulin treatment.