July 6, 2020

expert reaction to reports of a case of bubonic plague in Inner Mongolia

There have been reports of a case of bubonic plague in Inner Mongolia.

Prof Jimmy Whitworth, Professor of International Public Health, London School of Hygiene & Tropical Medicine (LSHTM), said:

“Bubonic plague regularly occurs in Mongolia. It normally affects wild rodents and is spread by infected fleas. Humans occasionally get infected if they come into contact with the rodents – in this case marmots- or fleas. While plague causes severe illness, if it is recognised promptly then it can be easily treated with antibiotics and patients will make a full recovery. The press reports indicate that this is the case in Inner Mongolia now, suggesting that there is no risk to public health. Two cases of plague were identified in Beijing last year in travellers from Mongolia and were quickly treated with no further spread of infection.

“As well as Mongolia, this disease occurs in other parts of the world, including the USA. Because plague is a disease of wildlife, it is very difficult to eliminate it completely. With the pneumonic form of plague, there is a risk of direct transmission from human to human, as was seen in the large outbreak in Madagascar in 2017.”    

Dr Michael Head, Senior Research Fellow in Global Health, University of Southampton, said:

“Bubonic plague is a thoroughly unpleasant disease and this case will be of concern locally within Inner Mongolia. However, it is not going to become a global threat like we have seen with COVID-19. Bubonic plague is transmitted via the bite of infected fleas, and human to human transmission is very rare.”

Prof David Mabey, Professor of Communicable Diseases, London School of Hygiene & Tropical Medicine (LSHTM), said:

“This is not worrying at all. We know there are rodent reservoirs of Yersinia pestis, the cause of plague, in Mongolia and a number of other countries, including the USA, and occasional human cases are reported in those areas where there are infected rodents. It is transmitted from rodents to human by flea bites.  There were a number of cases recently in Madagascar where it was suspected there might have been human to human transmission due to so called pneumonic plague, when the infection spreads via the blood stream to the lungs, but this was never proven.  Y. pestis remains fully susceptible to a number of antibiotics.”

Dr Matthew Dryden, Consultant microbiologist, Hampshire Hospital NHS Trust, University of Southampton & Rare and Imported Pathogens Department, PHE said:

“The report seems to be of a suspected case in Mongolia. It is good that this has been picked up and reported at an early stage because it can be isolated,  treated and spread prevented. Bubonic plague is caused by a bacterium and so unlike covid-19 is readily treated with antibiotics. So although this might appear alarming, being another major infectious disease emerging from the east, it appears to be a single suspected case which can be readily treated.

“I was involved in a localised outbreak in Gujarat, India in the 1990s. There was concern in the UK at the time that cotton waste from that area imported for the paper trade arrived in the UK infested with fleas which may have transmitted the illness. The cotton waste was contained and there were no human cases.

“There are seasonal cases in Madagascar most years.

“The last outbreak (about 8 people) in the UK was close to the port in the river Orwell in Suffolk in 1907.

“The plague bacillus is still present in many parts of the world including the USA usually amongst rodents such as prairie dogs and marmots in grassland habitats. It occasionally spreads to humans when there is direct contact between infected animals or their fleas and man. The risk of transmission to and explosive outbreaks amongst humans, as happened in the middle ages and up to the antibiotic era, is very unlikely at present as the bacterium causing plague remains sensitive to antibiotic treatments. It is important that we use antibiotics appropriately and sparingly to retain the activity of these important drugs.

“What kills patients quickly is the septicaemic illness (the bugs in the bloodstream). The bubos, as in bubonic, are the swollen lymph glands in the groin and armpits that may suppurate and release pus.”

Prof Malcolm Bennett, Professor of Zoonotic and Emerging Diseases, School of Veterinary Medicine and Science, University of Nottingham, said:

“Bubonic plague is caused by the bacterium Yersinia pestis, which circulates naturally in various wild rodents, transmitted by fleas, in particular in central Asia, parts of Africa and Madagasar and N. America.  Where these wild rodents live in relatively unpopulated (by people) areas, the infection rarely spills over into people.  However, the epidemiology of infection in these rodents often involves cycles of rodent population size and of  infection, and it is these cycles plus contact with humans  – direct or via other animals with closer contact with humans, such as pets in N America or peri-domestic rodents such as brown rats – that can lead to larger outbreaks in people. Particularly large outbreaks, or even epidemics, in humans can occur either when lots of peri-domestic rodents (such as brown rats) are infected, so lots of animal-human transmission can occur, or when people develop the respiratory form of the disease – pneumonic plague – which enables human-to-human transmission (so it stops being a zoonotic infection, and becomes a human one).  

“In other words, the drivers of plague emergence and re-emergence are similar to the drivers of other emerging diseases (such as Covid-19) – the infection is already there, mainly causing little problem to humans, but changes in its epidemiology and, in particular, changes in how we interact with it either directly or through other animals, can lead to more ‘spill over’ to people and possibly even human-to-human transmission. Although some areas have, in the past, undertaken lots of surveillance of plague in wildlife in order to identify when the risk to human health might increase, the expense of this means that in many places nowadays the focus is on identifying  human cases as soon as possible, both so that those individuals can be treated and their sources of infection can be investigated and control measures put in place – which the reports so far suggest to have been the case here.

“So individual human infections occur fairly frequently in central Asia and N America, and there are ongoing epidemics in parts of Africa and Madagascar, but these haven’t spread further in recent years.  The last pandemic was in the 19^th Century, and the most recent outbreaks of plague in Britain were in the early 1900s, when there were outbreaks in Glasgow which appear to have been driven largely by human-to-human transmission, and in East Anglia, when people got infected from local wildlife.”  

Prof Christl Donnelly, Professor of Applied Statistics, University of Oxford and Professor of Statistical Epidemiology, Imperial College London, said:

“Commonly available antibiotics are effective at treating plague.  Sometimes antibiotics are given preventatively to close contacts of cases.  Most cases of plague in the last 30 years have been recorded in Africa. However, small numbers of plague cases occur annually in the United States, usually in rural areas of western states. “

Dr Alexander Edwards, Associate Professor in Biomedical Technology, Reading School of Pharmacy, University of Reading, said:

“The immediate level of concern should not be high for this specific case of plague bacteria, as we still have effective antibiotics for many of the most threatening bacterial infections including Yersinia pestis which causes bubonic plague. Public health measures such as hygiene and safe drinking water are also still very effective for some many important ‘outbreak bacteria’ such as cholera and typhoid.

“However, there remains the looming threat of antimicrobial resistance (AMR) i.e. resistance to antibiotic drugs. AMR could reverse the last ~80 years progress in preventing deadly bacterial pathogens, if we lose our precious antibiotic drugs and these pathogens become drug-resistant.

“We’ve heard a lot about AMR over the past 5-10 years, if you remember superbugs (MRSA) in hospitals as well as more recent campaigns, and the UK has significant investment into research and innovation to combat AMR. But the current COVID-19 pandemic should really put this into sharp focus, as we still have time to prepare and put in place a wide range of measures to prevent antibiotic resistance and to be able to minimise the health and economic impact of drug-resistant bacteria.

“But new antibiotic resistance ‘tricks’ are constantly evolving in bacteria, and these can spread surprisingly rapidly across the world. Some of these make it much harder to treat bacterial infection. Often the resistance can spread between bacteria. We have learned recently quite how fast an emerging threat can spread globally- before we forget this lesson, we must apply what we have learned to antibiotic resistance.

“We must act now and follow the range of strategies the UK government and global health networks have identified, and make sure we aren’t underprepared for emergence of new resistance and/or spread of known resistance.”

Declared interests

Prof Jimmy Whitworth: No conflicts of interest.

Dr Alexander Edwards: Al Edwards is co-founder and director of a business developing rapid antibiotic resistance testing technology, and holds a current Innovate UK grant to develop this technology to detect AMR.

None others received.