A field of brightly-coloured, flowering poppies is as spectacular to the brain as it is to the eye. Opioids, drugs derived from the opium poppy, act on receptors in the brain to bring about sensations such as euphoria and pain relief. Just as the wind through a field of poppies can capture your gaze and keep you mesmerized for hours, so too can opioids hook your brain; a phenomenon well understood by heroin addicts. Sadly, euphoria and pain relief are not the only opioid-induced effects. Another side-effect blocks the drive to breathe, resulting in the death of an estimated 69,000 people worldwide each year.
Opioids block pathways in the brain that regulate breathing and dampen the feedback loops that tell the brain to take deeper breaths or more breaths when oxygen levels are low. Without enough oxygen in our blood, cells die and ultimately the heart will stop beating.
While opioid use in humans, with the subsequent consequences, is well recognized, opioid use in wildlife is perhaps not so widely understood. Have you ever wondered how wildlife veterinarians capture, treat and transport enormous wild animals such as rhinoceros and elephant? How do vets make these two-ton (or more) animals sleep by firing a measly dart into them? The secret lies in those fields of brightly-coloured poppies. Potent opioids, such as a drug commonly referred to as M99, are an essential component of a wildlife vet’s armory and the only class of drug capable of bringing about a deep sleep (or immobilisation) in large herbivores like the rhino and elephant. A major advantage of opioids is that their effect can be reversed with an antidote. When a vet has finished working with an animal, she injects the antidote and within seconds to minutes, the sleeping beast is awake and wandering back into the African bush.
However, the picture is not always so rosy. Sometimes the animals don’t get up, or sometimes they get up, only to suffer consequences of the event in days, weeks or months to come. It so happens that the white rhinoceros, currently needing the most hands-on interventions in the face of escalating poaching levels, is one of the species that is most severely affected by M99’s ill-effects. Just as opioids can kill humans, so too can they kill wildlife, with the white rhino being particularly susceptible to this fate.
White rhino are so severely affected by M99 that vets have been experimenting with different treatment options in an attempt to improve the oxygen levels in the immobilised rhino’s blood and reduce the risk of death. However, with many different vets trying variations on a similar theme, one standard approach, scientifically proven to improve oxygen levels, has been lacking. Therefore, with a team of researchers from the University of the Witwatersrand (Wits), University of Pretoria and SANParks, I systematically tested different available treatment options, firstly in boma-housed rhino and then in free-ranging rhino within the Kruger National Park. In the bomas, we were surprised to find that giving a high volume of oxygen through the rhino’s nostril made the physiological imbalances caused by M99 even worse and did not improve breathing. Another treatment option, currently used by many veterinarians, is a drug called butorphanol. Butorphanol partially reverses the effects of M99, and it is believed that the negative side-effects are reversed more than the positive effects, such as immobilisation. However, the advantages of butorphanol are not clear-cut and, invariably, some arousal occurs together with improved breathing. In a two-ton, confused wild rhino, unwanted arousal can be problematic. We also found that butorphanol did not fully correct the oxygen levels in the rhino. So we combined the administration of oxygen through the nostril with an injection of butorphanol. To our delight, this treatment option completely corrected the dangerously low oxygen levels, thus significantly improving the safety of rhino immobilisation.
As the fight against poaching intensifies, more rhino need to be immobilised for procedures such as translocation and the fitting of tracking devices. Moreover, vets are increasingly faced with severely injured rhino that have survived a poaching incident. These compromised animals require repeated immobilisations for intensive veterinary care and often cannot survive any additional physiological stress. Thankfully, as a result of our research, rhino capture need no longer be such a risky procedure and wildlife vets across South Africa have already adopted the approach of administering oxygen and butorphanol to immobilised rhino.
Haw AJ, Meyer LCR, Fuller A. 2016. Nalbuphine and butorphanol reverse opioid-induced respiratory depression but increase arousal in etorphine-immobilized goats (Capra hircus). Veterinary Anaesthesia and Analgesia.
Haw AJ, Hofmeyr M, Fuller A, Buss P, Miller M, Fleming G, Meyer LCR. 2015. Butorphanol with oxygen insufflation improves cardiorespiratory function in field-immobilised white rhinoceros (Ceratotherium simum). Journal of the South African Veterinary Association, 86: Art #1276.
Haw AJ, Hofmeyr M, Fuller A, Buss P, Miller M, Fleming G, Meyer LCR. 2014. Butorphanol with oxygen insufflation corrects etorphine-induced hypoxaemia in chemically immobilized white rhinoceros (Ceratotherium simum). BMC Veterinary Research, 10:253.