Ebola: Back in the DRC

August, 1976. A new infection was causing panic in Zaire. Hospitals became death zones, as both patients and medical staff succumbed to the disease. Reports of nightmarish symptoms trickled in to scientists in Europe and the US, who sent investigators to determine the cause and stem the epidemic. Concurrently, they would find out, the same thing was happening hundreds of miles to the north in Sudan. In all, 284 would be infected in that country, and another 358 in Zaire–over 600 cases (and almost 500 deaths) due to a mysterious new disease in just a few months’ time.

The new agent was Ebola, but remarkably, the outbreaks were unrelated, at least as far as any direct epidemiological links go. No one had brought the virus from Sudan to Zaire, or vice-versa. Molecular analysis showed that the viruses causing the outbreaks were two distinct subtypes, subsequently named for their countries of origin, Ebola Zaire and Ebola Sudan.

While Uganda is currently battling another outbreak of Ebola Sudan, rumors in the past week have suggested that this virus may have spread to former Zaire (now the Democratic Republic of Congo), where Ebola has reappeared 4 additional times since the first discovery there in 1976. It’s now been confirmed that Ebola is again present in the DRC, with an (unconfirmed) 6 deaths. However, it’s not related to the Uganda outbreak. Reminiscent of 1976, the strain that’s circulating currently in the DRC is the Bundibugyo subtype, which was first identified in Uganda in a 2007-8 outbreak in that country, rather than the Sudan type causing the current Ugandan epidemic. Interestingly, every previous outbreak of Ebola in the DRC has been caused by the Zaire type of Ebola, so the appearance of Bundibugyo is a first–though not altogether surprising given that the outbreak province borders Uganda.

Is this just coincidence that Ebola has twice now broken out in two different places at the same time, but with different viral subtypes? Hard to say. Though we can now say it’s fairly likely that bats are a reservoir host for Ebola and other filoviruses, we can’t say for sure that bats are the *only* reservoir. Indeed, we know that some outbreaks have occurred because the index case was in contact with an infected ape or their meat–were these animals originally infected by a bat, or by another source? How does the ecology of an area affect the chances of an outbreak occurring? Were there reasons that humans might be increasingly exposed to the virus in these different areas–Zaire and Sudan in 1976, DRC and Uganda in 2012–at the same time? Weather conditions? Trade/industry? Host migration or dispersal? We know with another bat-borne virus, Nipah, that changes in farming practices led to increased proximity of fruit bats and farmed pigs–allowing pigs to come into contact with virus-laden bat guano, become infected with Nipah, and subsequently transmit the virus to farmers. Things that may seem completely inconsequential–like the placement of fruit trees–can actually be risk factors for viral emergence. Is there a common factor here, or just bad luck? Only additional hard-won knowledge of filovirus ecology will be able to tell.

Comments

  1. #1 mo
    August 18, 2012

    …Fruit bat population peak?

  2. #2 Interface
    London, uk
    August 19, 2012

    Ebola comes from animals. Other nasty pathogens also come from animals. This occurs especially in hotspots such as tropical Africa, DRC, Uganda.

    I suspect that all of DRC has fewer than 10 veterinarians to diagnose animals whose diseases jump to humans.

    We wait for the disease to spread among people. Instead we should control the disease in animals, at the source before the pathogens spread at an exponential rate in the human population.

    Again, how many veterinarians are there in DRC working on public health risks? How many Ugandan veterinarians are there to do early warning and early disease control at the animal source in Uganda?

    A zoonotic disease is a disease jumping from animals to humans. Like Ebola and Nipah and AIDS and flu and rabies.

  3. #3 Tara C. Smith
    August 19, 2012

    mo, possibly–no idea. Interesting that in 1976 this also occurred in late August/September–environmental/climate influence?

    Interface, one problem with this is that it’s a wildlife reservoir, and one where the animals carrying it don’t have overt disease. So how do you control an asymptomatic infection in a wild species? We can’t even do that well in the US with all our resources–that’s why we vaccinate dogs and livestock against rabies, rather than try to control it in bats (who are the ultimate reservoir). Even trying to vaccinate other susceptible wildlife is very expensive and doesn’t always work the greatest. Agreed it would be great to control it somehow in animals to protect humans, but I don’t think we have the knowledge to do that right now.

  4. #4 Connor Bamford
    United Kingdom
    August 19, 2012

    The issue with ebola has always been interesting. I don’t think it is to do with the virus mutating and being able to spread outside of bats so it must be an ecological change.

    With the case of ebola and other filoviruses, there isn’t a massive amount of surveillance/ecological work done outside of humans. To really answer the question properly you would have to track the virus in and around the Congo Basin and rainforest (remember that a single continuous forest spans Africa from Cote d’Ivore to Uganda) and look where geographical it is, what species/populations it is in and then how much virus is present. You would also link it to ecological factors, such as increase in precipitation/primary production, bat population cycles or even primate/deer numbers.

    Ebola is clearly such a complicated problem and one that there’s a gap in the literature. But to do this kind of work in a Central African rainforest is not easy!

    There is a company called VaccinApe who are aiming to vaccinate gorillas against the virus. This virus a tiny problem for humans but a massive one for endangered primates!

  5. #5 Ed Rybicki
    South Africa
    August 20, 2012

    Nice to see intelligent commentary on Ebola! And an appreciation of the geography and distances involved, and the sheer enormity of trying to do what amounts to sophisticated epidemiology in a country the size of the DRC, to say nothing of a wider area bigger than western Europe.

    It turns out DRC does in fact have reasonably advanced diagnostics and surveillance capability for filo- and other zoonotic viruses – as we heard at our Virology Africa Conference in Cape Town back in November, for the head of Veterinary Services in that country. They also work quite closely with the National Institute for Communicable Diseases in Johannesburg and the CDC, so accurate diagnosis and identification is pretty quick.

  6. #6 Vince Whirlwind
    August 24, 2012

    Interface: don’t forget Hendra. Also comes from bats. 60% fatality rate, and this in the presence of 1st-world medical intervention.

  7. #7 Tara C. Smith
    August 24, 2012

    If you’re interested in Hendra, might want to mosey on over to this post instead. :)

  8. #8 Elliott Garber
    September 29, 2012

    Interesting idea about vaccinating endangered primates against Ebola, but I wonder if that would be stepping over the line in interfering with a natural cycle of disease? Or could we justify it given the human race’s otherwise huge negative impact on great ape populations? I wonder who would be given authority for such an intervention?

  9. […] of the more recent outbreaks in the Democratic Republic of Congo and Uganda have had much smaller numbers of cases than earlier outbreaks in these countries […]

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