Zimbabwean Elephants Succumb to Septicemic Infection Caused by Unknown Bacterium

The death of hundreds of elephants in southern Africa last year sparked global concern and raised questions about the causes and consequences of such a mass mortality event.

While the deaths in Botswana were attributed to cyanobacterial toxins, the deaths in Zimbabwe remained a mystery until now.

A team of scientists have recently discovered a rare and deadly bacterium that could be responsible for killing 35 elephants in north-western Zimbabwe.

This finding has implications for elephant conservation and health, as well as for understanding the ecology and transmission of this emerging pathogen.

A rare and deadly bacterium could be the culprit behind the mass mortality of African elephants

(Photo : BIJU BORO/AFP via Getty Images)

A team of scientists from Zimbabwe, the UK, and South Africa have uncovered the possible cause of the mysterious deaths of 35 elephants in north-western Zimbabwe last year.

The researchers found evidence of a septicemic infection caused by a little-known bacterium provisionally named Bisgaard taxon 45, an unclassified member of the Pasteurellaceae bacterial family, in six of the dead elephants.

This bacterium is closely associated with deadly septicemia, a condition where bacteria multiply in the bloodstream and cause organ failure.

The findings, published in the journal Scientific Reports, place infectious diseases on the list of pressures on African elephants, whose populations continue to be under threat from poaching, habitat loss and climate change.

African savanna elephants are an endangered species with only 350,000 remaining in the wild and ongoing losses estimated at eight percent annually.

This finding is very worrying since elephants are on the International Union for Conservation of Nature red list already.

The scientists investigated the deaths of 35 elephants mostly between August and September 2020, in a 40 x 25 km radius of north-western Zimbabwe.

This incident followed the death of approximately 350 elephants in neighboring northern Botswana from May to June 2020, which triggered much international concern.

The Botswana government later attributed the deaths to cyanobacterial toxins in waterholes, but some experts questioned this explanation and called for more investigations.

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The investigation faced many challenges and ruled out several possible causes

Lead investigator, Dr. Chris Foggin, a wildlife veterinarian at the Victoria Falls Wildlife Trust, said that investigating this mortality in the wildlife areas in northwest Zimbabwe proved challenging.

He said that identifying and reaching the carcasses in time to obtain useful samples was one problem they often faced in this type of work.

He further said that they did not know what disease they may be dealing with, although they initially suspected that it could be anthrax, which is known to occur in the area; or possibly some other disease that might pose a risk to human health.

Moreover, Foggin said that they had to be cautious when undertaking the post-mortem examinations on elephant which, in itself, is a difficult task with such a big animal, especially working in field conditions.

A number of such postmortem examinations were carried out. Poaching was quickly ruled out, mainly because all the dead elephants had their tusks intact.

Toxicology analyses, including immediate testing for cyanide, which is sometimes used to kill elephant in Zimbabwe, as well as more sophisticated analyses done in UK, found no traces of poisons in the carcasses or at a waterhole close to many of the carcasses.

Further examination by veterinarians and scientists identified a septicemic infection caused by Bisgaard taxon 45 in six elephants.

This was confirmed by bacterial isolation and genetic analysis. Only a limited amount of samples were suitable to carry out such examinations.

Pasteurella bacteria have previously been implicated in sudden deaths of wild animals such as antelope, but a role in elephant deaths was not suspected prior to this study.

The researchers suggested that Bisgaard taxon 45 could have entered the elephants' bloodstream through wounds or abrasions caused by environmental factors such as drought or fire.

They also speculated that stress or malnutrition could have weakened the elephants' immune system and made them more susceptible to infection.

The researchers acknowledged that their study had some limitations, such as the small sample size and the lack of information on the clinical signs and epidemiology of the disease.

They also noted that Bisgaard taxon 45 may not be the sole cause of death, but rather a contributing factor or an opportunistic pathogen.

They called for more research to understand the ecology and transmission of this bacterium and its impact on elephant health and conservation.

Dr. Foggin said that their study highlighted the importance of monitoring wildlife health and conducting timely investigations into unusual mortality events.

He said that this would help to identify emerging threats and implement appropriate management interventions to protect wildlife populations.

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