MANAGEMENT, CONTROL AND REGULATIONS

VACCINES

The veterinary vaccines currently used to control anthrax are composed of spores from attenuated strains of B. anthracis. They are classified into two categories:

• live attenuated vaccines, capsulated and without toxins, cap⁺∕tox^- (e.g.

• live attenuated vaccines, not capsulated with toxins cap^-∕tox⁺ (e.g. Sterne and STI vaccines).

The Pasteur vaccine is characterized by a plasmid pattern pXO1^-∕pXO2⁺. The Pasteur vaccine type 1 is not patho­genic for guinea pigs but is pathogenic for mice. The Pasteur vaccine type 2 is pathogenic for both guinea pigs and mice, but is not pathogenic for rabbits. Pasteur vac­cines should not produce toxic factors and were used in the past, when they routinely produced a 3% mortality. Now only a few countries use this vaccine.

Sterne vaccine was produced for the first time in 1939(¹⁰). It is very protective. The attenuation is due to the loss of plasmid pXO2, encoding the capsule synthesis; the spores germinate in the vaccinated animals. Non- encapsulated vegetative forms multiply, produce toxic factors and are then neutralized by phagocytes. This allows synthesis of enough toxins to stimulate the protective immunity, but insufficient to damage the host. The animal vaccines that use Sterne strain 34F₂ are formulated with approximately 107 spores per ml suspended in 0.5 ml 50% glycerine- saline. The protective effect of a single dose of strain 34F₂ vaccine is expected to last about 1 year, and an annual booster is recommended for livestock in endemic areas.

Anthrax control and eradication programmes involve targeted livestock vaccination, farmer awareness and prompt reporting of unexpected deaths, and the correct management of infected carcasses. Incineration in situ is the best method to reduce the contamination level of soil. It should be considered a global responsibility to imple­ment anthrax control and eradication programmes, rather than restricting the control to emergency situations.

Vaccination of Wildlife

Administering injectable vaccines to wild animals requires their immobilization or vaccination by darting. Prelimi­nary studies on oral vaccines indicate that they may be protective, but it is difficult to get wild herbivores to take up baits. The recent demonstration of the efficacy of plant- expressed Bacillus anthracis protective antigen will open up a new area of research in the mass vaccination of domestic and wild animals that live in high-risk areas for anthrax(¹¹).