Vaccines to reduce possum fertility

Researchers in New Zealand, at AgResearch, Landcare Research, Victoria University and Otago University, investigated vaccines that would make possums less fertile.

Possums are New Zealand’s main vertebrate pest. They threaten New Zealand’s flora and fauna and can spread tuberculosis (Tb) to farm animals. Vaccination is one of several biocontrol methods that were tested for their ability to reduce possum numbers in New Zealand.

How do the vaccines work?

The vaccines act as a contraceptive. They make a possum’s immune system produce antibodies against its own reproductive proteins. The antibodies then destroy the proteins, so the reproductive system stops working and the possum cannot have any young.

Find out more in these articles:

• Making contraceptive vaccines for possums
• Delivering biocontrol agents to possums
• Possum vaccines and reproductive proteins

Are all possums affected?

The main target of the contraceptive vaccines is female possums, however some vaccines may also affect males. The reason females are targeted is because even if 90% of males were made infertile, the remaining 10% could still breed and maintain the same population level.

Advantages of reducing possum fertility with a vaccine

• Vaccines are effective. In a trial vaccinating possums against the reproductive protein, GnRH, 70% of possums were infertile two years after receiving the vaccine
• Vaccines are humane. Contraceptive vaccines do not cause the possums’ pain or distress. The possums are perfectly healthy and live a normal lifespan.
• Vaccines do not affect other animals. The risk to non-target species is minimal because efforts are made to make the vaccines as specific as possible for possums. Also, vaccines can be delivered using species-specific bait stations, so other animals like native birds are unaffected. However, if another species was exposed to the vaccine, it may be possible to reverse the effects.
• Vaccines are environmentally friendly. Vaccines are not toxic and will not pollute the environment.

Disadvantages of reducing possum fertility with a vaccine

• Currently, vaccines only last for a few years at best. After initial vaccination, the antibodies in the possums’ bodies will gradually decrease. After two to three years, the possums will need to be vaccinated again, which will cost money.
• Vaccines are expensive and time-consuming to develop. However, any new possum control method would be expensive and time-consuming to develop.
• A genetically modified organism may be used as a carrier to take the vaccines to the possums. This may be unacceptable to some people.

An update

In a 2011 report, Dr Jan Wright, Parliamentary Commissioner for the Environment wrote that although significant research effort and resources were put into possum contraceptive vaccines and hormone toxins, funding for the projects finished in September 2010. There was concern about the length of time required to produce results, risks associated with the biocontrol agents and potential controversy over genetic engineering.