- Earlier this year, more than 350 elephants mysteriously died in the Okavango delta in Botswana.
- Individuals of all ages and both sexes were affected, with many walking in circles before dying suddenly, collapsing on their faces.
- The mass die-off in May and June was described as a “conservation disaster”.
- Elephants are now reported to have started dying in a similar way in neighbouring Zimbabwe.
- There have been many competing theories about the cause of the deaths in Botswana.
- Human-elephant conflicts are common in the Okavango delta, an agricultural area home to 15,000 elephants and 16,000 people, but poisoning or poaching are unlikely to be to blame.
- Cyanide was ruled out because no scavengers died and tusks were left intact, according to a commentary piece co-authored by Bengis in the African Journal of Wildlife Research.
- Pesticides and anthrax were tested for and also ruled out.
- After months of work, scientists have whittled the cause down to two leading theories – neurotoxins in algal blooms or a rodent virus known as EMC (encephalomyocarditis).
Algal blooms
- Local sources estimate that 70% of elephants in Okavango in Botswana died near waterholes, many of which contained blue-green algal blooms.
- Toxins from algae were initially ruled out as a potential cause because elephants were the only species to die (with the exception of one horse).
- Now experts think elephants could be more vulnerable to algal bloom toxins because they spend so much time bathing and frolicking in water.
- Their long trunks also have a large number of olfactory receptors and they can drink hundreds of litres of water a day, potentially exposing them to more toxins than other species.
- They could be caused by a recently discovered bacterial toxin produced by algae called BMAA (beta-methylamino-L-alanine).
- BMAA is mainly found in marine environments (as opposed to fresh water).
- Zebra, wildebeest, white rhinoceros and impala have all died from ingesting toxic algae but there is no literature about elephants dying from neurotoxins in algal blooms.
- This might be because pathologists and vets do not initially test for cyanobacteria, and once they decide to do so it is often too late because the tissues have deteriorated or the algal blooms have gone.
- Rising temperatures and intensive farming methods are fuelling an increase in algal blooms in rivers, lakes, reservoirs and seas around the world.
- Elephants are naive to this potential threat which makes them vulnerable.
Rodent virus
- The fact that the elephant carcasses were close to water holes does not mean water was the source of the poison – frequently sick animals seek out water because they are feverish or thirsty.
- Farming is widespread on the floodplains of the Okavango delta and this year has seen a bumper crop of maize and sorghum because of late rains in 2020 following a string of dry years.
- This could have attracted families of elephants to cropland as well an increase in rodents, which defecate and urinate on tufts of grass.
- This means they would have been in close contact.
- Most grazers eat the leaf part of grass, but elephants grab grass with their trunk and eat the whole tuft (including rodent faeces), potentially exposing them to the EMC virus.
- Unlike neurotoxins, EMC is a fairly well-known pathogen that most frequently affects elephants in zoos where there are lots of rats – there have been several cases in US zoos and one in Australia.
- It caused the death of 64 elephants in Kruger national park between 1993 and 1994.
- Like neurotoxins that can kill in as little as 20 minutes, EMC is a quick death that causes elephants to collapse on their feet (although it can incubate for for five to 10 days, so elephants can move long distances in that time).
- The single dead horse could be a clue – not a coincidence – as horses are also vulnerable to EMC.
- The Botswana government has ruled out EMC because there was no damage or abnormalities found on heart tissue of the animals, but it is not clear how many samples were tested.