Vaccination halts tumour growth in rhinos
“If the oestrous cycle of female rhinoceros can be interrupted by a simple inoculation and, later on, fertility can recover again, the vaccination is a huge veterinary advance."
For the first time a vaccination has successfully stopped the growth and regeneration of innocuous tumours in rhinos, researchers say.
Southern white rhinos and greater one-horned rhinos were injected with the ‘Improvac’ serum, which affects the release of hormones and causes the female oestrus cycle to cease, thereby reducing hormone-dependent tumours.
Three months after the vaccination, scientists say ultrasound examination showed a reduction in tumour size to half its original size. And after a year, no more new growths were detected. The findings have been published in the journal PLOS ONE.
Female rhinos often suffer from vaginal or uterus tumours which complicate the process of reproduction. Whilst they are largely innocuous, if they grow too much the animal may have reduced fertility, or become completely infertile. Tumours can cause pain during mating and lead to problems with conception, as well as miscarriages and stillborns. However, it is not possible to cut out large tumours owing to the rhino’s thick skin.
Improvac is a hormone that relates to the body’s gonadotrophin-releasing hormone (GnRH), which regulates the release of sexual hormones from the hypophysis and, therefore, ovulation and ovarian activity.
After vaccination, antibodies are produced that block GnRH so the hypophysis stops releasing sexual hormones and the oestrus cycle and female fertility cease. As a result, scientists say hormone-dependent tumours stop growing and reduce in size.
Tumour risk is linked to whether or not rhinos have previously had offspring. Gestation at an early age prevents reproductive organs from forming tumours and existing tumours stop growing when an animal gets pregnant. As a result, researchers from the Leibniz Institute for Zoo and Wildlife Research believe early reproduction of rhinos should be promoted.
Robert Hermes, an expert in reproductive medicine and rhinos from the institute, said: “If they are not able to have offspring because of external circumstances, for instance in the absence of an available mate, a vaccination could help prevent tumour formation.
“The sexual cycle is put ‘on ice’ and can be reactivated for pregnancy later on without loss of the female’s fertility or the risk of tumours.”
Further study will be needed to determine whether the vaccine’s effects are completely reversible. The same treatment has already been successfully used in horse mares, who became fertile again with a normal sexual cycle some time after vaccination.
Hermes continued: “If the oestrous cycle of female rhinoceros can be interrupted by a simple inoculation and, later on, fertility can recover again, the vaccination is a huge veterinary advance. This is a great benefit, particularly with regard to the future health care management of rhinos in human care.”
RCVS Knowledge has welcomed Professor Peter Cockcroft as editor-in-chief for Veterinary Evidence. 
