An application is about to be submitted to the Australian Pesticide and Veterinary Medicines Authority (APVMA) seeking authority to launch "Barbervax", a novel vaccine to aid in the control of Haemonchus contortus, commonly known as the Barber's pole worm. This parasite is an important cause of death and disease in sheep and goats both in Australia and in other tropical and sub-tropical parts of the world, more especially as isolates known to be resistant to one or more class of anthelmintic drug are common and widespread.
Fairly recently, a new class of anthelmintic was launched in Australia with a second currently being reviewed by the APVMA, but history suggests that Haemonchus resistant to these are likely to emerge within a decade or so. Barbervax has more prolonged activity than either of these new drugs, works against anthelmintic resistant Haemonchus and, since it is considered unlikely that worms resistant to the vaccine will emerge, it offers a more sustainable approach to control.
Unlike anthelmintics, which contain either a single or a small number of chemical actives (as in combination formulations), this vaccine has many protective antigens each with numerous epitopes. It is considered extremely unlikely that any Haemonchus exist which do not possess any of this plethora of target epitopes, more especially as it is known that the vaccine antigens are geographically conserved. For example, vaccine made from worms isolated in WA protected sheep in NSW, the UK, Brazil and Uruguay. Similarly, vaccine prepared from UK H. contortus works in Brazil and S. Africa and even against H. placei, a different species. No reports of parasite resistance have been published for either of the two existing metazoan parasite vaccines namely, Huskvac and Tickgard (or Gavac), despite both having been on the market for decades.
No commercial vaccines exist for any gut dwelling helminth parasite in any host. If approved, Barbervax will provide farmers with a completely novel way to control Barber's Pole worm. The vaccine can be integrated with anthelmintic drugs and other interventions for preventing parasitic gastroenteritis caused by other nematode genera. It can also be used with Clostridial vaccines and other commonly used sheep remedies for e.g flystrike. Like most other killed vaccines, no withdrawal period is expected.
Barbervax is made at the Department of Agriculture and Food laboratory in Albany, WA. The vaccine antigens are purified from adult Haemonchus obtained in kilogram amounts from deliberately infected donor sheep. The antigen is formulated with adjuvant to produce the vaccine which is bottled in 250 ml multi-dose pillow pack containers. The complete process from sourcing the donor sheep to bottling the vaccine has an APVMA Good Manufacturing Practice licence.
Barbervax is a killed vaccine and therefore safe. It has a shelf life of at least two years when stored refrigerated. Each dose contains only 5ug of purified antigen formulated with one mg saponin, an immunological adjuvant widely used in existing vaccines for livestock. Apart from a mild transient fever and variable skin thickening at the injection site, Barbervax provokes little reaction in the host and can be given to heavily pregnant ewes or to month old lambs with no ill effects.
The vaccine is easy to use, each dose being a one ml subcutaneous injection irrespective of the weight of the sheep. However, repeated vaccination is needed to maintain protective immunity because the immune response to the vaccine is not boosted by natural infection with the parasite.
Efficacy field trials with some 240 lambs on six different farms in Australia indicated that Barbervax could reduce Haemonchus faecal egg counts by an average of about 80% over the summer "season". This figure is an underestimate of the impact of the vaccine partially because almost all the control lambs in the trials received at least one dose of anthelmintic to prevent fatal anaemia. This intervention obviously underestimated their true egg counts because although some vaccinates also needed treatment, the proportion was much smaller. In addition, because the vaccinates grazed with the controls they were subjected to a much higher challenge than if they had grazed alone. Co-grazing was done to ensure both groups received an identical challenge infection, but in practice all farmers would be advised never to graze vaccinated sheep with unvaccinated ones.
When the field trial protection data was modelled, simulations using historical weather data over 20 years and vaccinated lambs grazing alone, indicated that the vaccine offered better Haemonchus control than a typical anthelmintic regime consisting of one persistent and three short acting drenches. The model also assumed that these anthelmintics were highly effective, a situation which is becoming harder and harder to guarantee.
Hopefully, Barbervax will provide Australian sheep producers with another tool to combat the scourge of Barber's Pole infestation in the not too distant future.