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How does the pZP vaccine work?

A membrane known as the zona pellucida (ZP) surrounds all mammalian eggs. This membrane contains several glycoproteins, one of which is thought to be the sperm receptor (the molecule which permits attachment of the sperm to the egg during the process of fertilisation). The PZP (porcine zona pellucida) vaccine is derived from pig eggs. Once injected, the vaccine stimulates an immunological response to produce antibodies that attach to the ZP of the target animal, thereby preventing fertilization as sperm cannot attach to and penetrate the egg.

The PZP vaccine is not a hormone! Therefore, to date, no observed behavioural or physiological aberrancies have been noted. All normal reproductive functions are maintained in the target animal, namely oestrous cycles, lactation and foetal development (in pregnant animals).

How is immunocontraception implemented?

First and foremost, a properly defined elephant management plan needs to be in place that will outline potential problems with regards to the elephant population and also make provision for their active management. Thereafter, it can be determined whether or not immunocontraception will be a viable management option for the reserve.

Target animals then need to be identified. This target group consists of the reproductively active females within a population. The vaccine can be administered remotely to free-roaming elephant, either from the ground or air. Important: The vaccine administration must reflect the conservation and ecological requirements of the specific reserve. Each of the target animals selected will receive an initial vaccination followed, three weeks later, by a booster. This will contracept the animals for one year. Thereafter, the animal will receive an annual vaccination consisting of one booster only.

The population should then be monitored on a regular basis so as to note any abnormalities. Re-assessment of the population should take place on an annual basis. Bare in mind that this is a biological control method aimed at slowing down and ultimately stabilizing an elephant population’s growth rate, and is not aimed at stopping births completely.

Immunocontraceptive results at Makalali Private Game Reserve

For the initial, 1st and 2nd vaccinations in 2000, 2001 and 2002 respectively, all the animals were darted from a vehicle or from foot. During this period, none of the elephants were radio-collared. However, 23 animals received their initial, primary, secondary and annual boosters remotely over a 3yr period. This proved that the PZP vaccine could be successfully and remotely delivered to free-roaming elephants in a small game park (refer to publications).

Behavioural, reproductive and spatial monitoring of the Makalali elephants has been underway since 1998. As a result, an extensive database exists on the animal’s seasonal movements, herd associations, bull/cow interactions and reproductive behaviour. To date, the only negative effect on behaviour has been an increasing wariness to the vehicle used for darting and a change in the herd’s spatial utilisation, primarily during the administration of the initial and subsequent booster vaccinations. However, soon after completion of the initial vaccination programme, the animals resumed normal movement patterns and were once again relaxed with the vehicles. No further behavioural anomalies have been recorded i.e. no separation of vaccinated females from family groups, herd fragmentation etc. Bull/cow interactions have occurred and recorded as normal.

The last target animal to have calved (as a result of being pregnant prior to contraception) was recorded in August 2002 (Delsink, personal observation). Thus, for the period August 2002 to July 2004, no contracepted cows have calved i.e. 0% growth has been achieved. However, to testing the reversibility of the vaccine, a number of treated cows were removed from the program. Two of these cows have subsequently calved illustrating that there are no side effects or concerns with the long-term treatment of the vaccine. Visit http://www.globalpost.com/dispatch/south-africa/090225/planned-parenthood-elephants for a video and update on the first reversal cow Smelly and her calf.
The Makalali study demonstrates that immunocontraception offers managers an alternative management tool that is safe, effective, reversible, non-lethal and practical in stabilizing elephant populations.

The advisors and participants of this project include:

1 The Humane Society of the United States (principal sponsors).

2 Ms Audrey Delsink and Mr Ross Kettles, Greater Makalali Private Game Reserve, PO Box 1009, Hoedspruit, 1380, South Africa.

3 Mr JJ van Altena, Catchco Africa, PO Box 1148, Highlands North, 2037, South Africa.

4 Prof. Henk Bertschinger, University of Pretoria, P O Box 75058, Lynnwood Ridge, 0040, South Africa.

5 Dr Jay Kirkpatrick, Science and Conservation Center, ZooMontana, 2100 South Shiloh Road, Billings, MT 59106, USA.