ZANZIBAR'S VIRAL UNDERGROUND

by Martin Walsh

The walkway between caves at Mchekeni, Zanzibar (photo: Martin Walsh)

I worry about caves. I’ve been worrying about them ever since reading about the role played by Kitum Cave in the known history of Marburg virus disease. In the 1980s, two separate visitors to this “elephant cave” in Mount Elgon National Park were infected and subsequently died. Egyptian fruit bats (Rousettus aegyptiacus) have since been identified as a reservoir host for marburgviruses, and it may well be that the inhalation of microbes from bat guano was the means by which these unfortunate tourists contracted the deadly disease.

I’m also fascinated by caves: they’re contagious in more ways than one. The islands of the Zanzibar archipelago, with their extensive limestone reef terraces, are riddled with caves and sinkholes. They’re a distinctive feature of the coral rag or karst landscape of both Unguja and Pemba, though often hidden from sight by thick vegetation, especially along the forested scarps in the south and east of the main island. Many of the caves have cultural significance as mizimu, the abodes of spirits that are regularly propitiated by the local guardians who have inherited this responsibility.

Entering one of the caves at Ufufuma (photo: Martin Walsh)

I wasn’t really aware of either the abundance of caves or the extent of this practice until Helle Goldman and I began researching knowledge and beliefs about the Zanzibar leopard (Panthera pardus adersi) in 1996. There’s a strong association between leopards and caves, because of the spiritual significance of both and the fact that leopards were believed to be often found in and around them. In some cases, leopards themselves are the spirits that subterranean offerings are made to. 

More recently, Maximilian Chami and others have begun documenting these and other sacred sites, though we’re far from possessing anything like an inventory or gazetteer. Following his father Felix Chami’s pioneering excavations, caves have also been providing us with remarkable insights into Zanzibar’s past, including the people and fauna of Unguja before it became an island. I’ve been a minor contributor to discussions about some of the emerging zooarchaeological evidence – and I look forward to more.

Unsurprisingly, some of the limestone caves on the eastern side of Unguja are now tourist venues. The impressive Mchekeni Caves, in the Kiwengwa-Pongwe Forest Reserve, have been open since 2006, though visitor numbers can be very low. Other caves have been developed privately. Kuza Cave in north Jambiani is more like a rock shelter or overhang (presumably exposed by an earlier collapse), with a beautiful turquoise pool that tourists are encouraged to swim in. The caves at Ufufuma, roughly halfway between Mchekeni and Kuza, are used by a traditional healer (mganga), who also entertains fee-paying tourists.   

Bats in the south cave at Mchekeni (photo: Martin Walsh)

Whenever I’ve visited Mchekeni, I’ve felt distinctly uneasy penetrating deep into the southern cave. This is not because there’s no path and it’s unlit, it’s because I’m thinking about bats. There are plenty of small bats clinging to the walls, harmless enough. But I can’t help but wonder about the viruses they might be carrying. Spillover events may be rare, but as the ongoing global pandemic has painfully reminded us, they can happen, and bats are, for better or worse, the reservoir hosts of numerous viruses, SARS-CoV-2 included.

Perhaps I should be more worried about the fruit bats hanging in the trees, and the fruit that they may have slobbered or defecated on. Or fretting about Pemba, where flying foxes (Pteropus voeltzkowi) and other bats have traditionally been hunted as bushmeat. Who knows what harms this may have caused in the longue durée of island history? Of course, Zanzibar has more pressing public health problems to deal with in the present. Sooner or later, though, Zanzibar and Tanzania will have to start thinking about the biosecurity of the growing number of caves on the tourist trail. Next time I go down there, I’m wearing a mask.

Further reading

Bardenwerper, Julie 2009. Spirits and Sacred Sites: A Study of Beliefs on Unguja Island. SIT Study Abroad, Independent Study Project (ISP) Collection. Paper 759.

Chami, Maximilian F. 2019. “Sacred Limestone Caves”: Management and the Use of Sacred Heritage Places in Limestone Cave Areas along the Swahili Coast of Indian Ocean in Tanzania. Unpublished PhD dissertation, Brandenburg University of Technology Cottbus–Senftenberg.

Chami, Maximilian F. & Felix A. Chami 2020. Management of sacred heritage places in Tanzania: a case of Kuumbi limestone cave, Zanzibar island. Journal of Heritage Management 5 (1): 71-88.

From the Kuza Cave website, www.kuzacave.com

Faulkner, Patrick et al. 2019. Long-term trends in terrestrial and marine invertebrate exploitation on the eastern African coast: insights from Kuumbi Cave, Zanzibar. The Journal of Island and Coastal Archaeology 14: 479–514.

Goldman, Helle & Martin Walsh 2019. Classifying, domesticating and extirpating the Zanzibar leopard, a transgressive felid. Norsk Antropologisk Tidsskrift 30 (3-4): 205-219.

Prendergast, Mary E. et al. 2016. Continental island formation and the archaeology of defaunation on Zanzibar, eastern Africa. PLoS One 11 (2): e0149565.

Quammen, David 2012. Spillover: Animal Infections and the Next Human Pandemic. London: Vintage Books.

Walsh, Martin 1995. Eating bats on Pemba island: a local innovation or cultural borrowing? Mvita: Newsletter of the Regional Centre for the Study of Archaeology in Eastern and Southern Africa 6: 15-18.

Walsh, Martin 2011. From green monkey disease to fruit bat viruses. East African Notes and Records, 26 December 2011.

Walsh, Martin & Helle Goldman 2007. Killing the king: the demonization and extermination of the Zanzibar leopard. In E. Dounias, E. Motte-Florac & M. Dunham (eds.) Le symbolisme des animaux: L'animal, clef de voûte de la relation entre l'homme et la nature? Paris: Éditions de l’IRD. 1133-1182.

FROM GREEN MONKEY DISEASE TO FRUIT BAT VIRUSES

Kenyans breathed a collective sigh of relief on Friday when it was announced that a 29 year-old woman who had bled to death in Kenyatta National Hospital the morning before was not the victim of an Ebola-like virus, as had initially been feared (for the Nation's version of these events, click here). As readers of Richard Preston's bio-thriller The Hot Zone (1994) were informed in full technicolour detail, Ebola and its congener, Marburg virus, don't take many prisoners. Typically more than half of the people who display symptoms of these highly infectious diseases die; in some outbreaks close to 90% of those infected have succumbed. The symptoms of these deadly viruses can be terrifying: some victims may suffer severe hemorrhaging, bleeding from all of their bodily orifices. And they don't always go quietly: some Ebola victims die an even more horrible death, thrashing about in a uncontrollable fit as they smear and splatter blood everywhere. Thanks in part to exaggerated accounts like Preston's, Ebola and Marburg elicit widespread fear, and panic when they are thought to be anywhere near.*

The recent scare reminded me of earlier Ebola panics. In 1980, during my first few weeks in Tanzania, overland travellers staying at the Moravian Youth Hostel in Mbeya came bearing hair-raising tales of what was then dubbed 'Green Monkey Disease', a killer infection that had led to periodic closures of the roads through the southern Sudan. Although I didn't know it then, this was a variety of Ebola, the virus named after its discovery in 1976 near the headwaters of the Ebola River in Zaire (now the Democratic Republic of the Congo, DRC). The first recorded Sudanese outbreak occurred in the same year, and killed more than 150 people. It was followed by another in 1979, and it was this recurrence (which resulted in 22 fatalities) that had affected the travel plans of my fellow hostellers. Otherwise I didn't really become aware of Ebola by name until the mid-1990s, when there were further cases in Zaire. The Kikwit outbreak in 1995, which killed 250 people, was widely reported in the press and was said to have led to tourist cancellations throughout the region, especially in countries and territories whose names also began with the letter 'Z' (like Zambia and Zimbabwe). One of these was Zanzibar, where I was living and working at the time.


The Ebola virus
(Dr. Frederick Murphy)

 The Ebola-Zaire strain is the most virulent of this family of thread-like viruses. The first of the filoviruses to be described was Marburg virus, named after an outbreak in a factory in the West German city of Marburg in 1967. The Hot Zone opens with a dramatic reconstruction of the first case in Kenya, which took place in 1980 when a Frenchman who worked at the Nzoia Sugar Factory died in Nairobi Hospital. Before dying he vomited blood over the Ugandan doctor who was treating him, and Dr. Shem Musoke was infected in turn. The presence of Marburg was detected in samples of Musoke's blood taken by a colleague, cardiologist Dr. David Silverstein, and after being close to death his life was saved. Silverstein is perhaps best known as former President Moi's personal physician, and as one of the leaders of the Jewish community in Kenya. Coincidentally I was treated by him some years later for a phantom blood clot, and it was Shem Musoke who did me the favour of diagnosing it as imaginary. But that's a story for another day.


Silverstein was also involved in the treatment and diagnosis of Kenya's second Marburg victim, a Danish boy who died in Nairobi Hospital in 1987. These have been the only confirmed incidents in Kenya to date, and it turns out that both of of the victims had visited Kitum Cave on the slopes of Mount Elgon not long before they fell ill. The Hot Zone ends with an account of author Richard Preston's foray into the cave wearing a protective suit, wondering which, if any, of its animal inhabitants or visitors might host the virus. For a time monkeys were implicated, not least because they were the immediate source of outbreaks of both Marburg and Ebola in laboratories on different continents. The first Marburg infections came from Vervets (aka Green monkeys, Chlorocebus pygerythrus, syn. Cercopithecus aethiops) imported from Uganda, and one of Preston's informants believed that there had been an earlier undocumented outbreak of Marburg among monkeys and people on the northern side of Mount Elgon. However, monkeys are evidently not the primary host of either Marburg or Ebola: like people, too many of them die too quickly during an outbreak for the viruses to spread more widely. Not that this has stopped Preston and other journalists from imagining a doomsday scenario involving international air travel...

Richard Preston preparing to enter Kitum Cave (author's website)

It turns out that the association with caves (and in some cases mines) is much more significant for an understanding of the natural reservoirs of Marburg and Ebola. In recent years a number of studies have detected the presence of these filoviruses in otherwise healthy cave-dwelling bats, suggesting that they are their main natural hosts. I've posted links to some of the relevant papers (most of them open access) in the references  below. Bats carrying Marburg and Ebola have been identified in Gabon (which has yet to suffer a recorded outbreak), DRC, and Kenya, and it seems likely that they will also be discovered in other African countries. The bats involved include a growing list of insectivorous species as well as the Egyptian fruit bat (Rousettus aegyptiacus), which has tested positive for both Marburg and Ebola. This is one of Africa's most common bats, known for roosting in large colonies in caves, unlike many other fruit bats. The good news is that health education can now be targeted at cave sites in national parks and other underground locations that receive large numbers of visitors. The bad news is that outbreaks of Marburg and Ebola are likely to occur in hitherto unsuspected places across the continent. At least last week's scare proved to be a false alarm.

Note
* For more sober information about Ebola and Marburg, including details of all the confirmed outbreaks, readers should refer to the Centers for Disease Control and Prevention website and the pages for Ebola Hemorrhagic Fever and Marburg Hemorrhagic Fever respectively.

References

Kuzmin, Ivan et al. 2010. Marburg virus in fruit bat, Kenya. Emerging Infectious Diseases 16 (2): 352-354.

Leroy, Eric M. et al. 2005. Fruit bats as reservoirs of Ebola virus. Nature 438: 575-576.

Pourrut, Xavier et al. 2005. The natural history of Ebola virus in Africa. Microbes and Infection 7: 1005-1014.

Pourrut, Xavier et al. 2009. Large serological survey showing cocirculation of Ebola and Marburg viruses in Gabonese bat populations, and a high seroprevalence of both viruses in Rousettus egyptiacus. BMC Infectious Diseases 9: 159.

Preston, Richard 1994. The Hot Zone. New York: Random House. [the link given here is to a complete typescript of the main text]

Towner, Jonathan S. et al. 2007. Marburg virus infection detected in a common African bat. PLoS ONE 2 (8): e764.