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A trial was conducted at Kruger National Park in South Africa to test the efficacy of immunocontraception using pig zona pellucida antigens (Fayrer-Hasek et al Nature 407: 149, 2000). Forty-one adult female elephants were located by helicopter and females identified as non-pregnant were anaesthetised by aerial darting. Twenty-one animals were vaccinated with 20 others serving as placebo controls. The animals were fitted with radio collars. Vaccinated elephants were located and received booster shots twice (once after 6 weeks and another at 6 months). The animals were recaptured 12 months after the initial vaccination and scanned for pregnancy. Two animals in each group were not located. Data from that study have been re-fashioned in the table below:


Pregnancies Vaccinated Placebos
YES 9 16
NO 10 2


Thus the relative risk of pregnancies in the non-vaccinated group was 1.89

In a later study, the authors used a revised schedule to vaccinate 10 more elephants and ten months later found that only 2 were pregnant. If these numbers were used in the calculations, the relative risk in the non-vaccinated group would increase to 4.45.


Immunocontraception in humans is a controversial issue. Placing the procedure in the context of wildlife populations enabled students to see the commonalities in approaches. They discussed the biological rationale for such approaches and compared and contrasted the technological and ethical aspects of applicability to humans and other mammals. A deeper exploration into the biology of elephant populations was undertaken by one group who considered the relations between elephants and humans and the impact of the trade in ivory. This proved to be one of the more exciting problems dealt with by the class that year.

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