Thursday, 14 May 2015

Liberia gave Ebola the boot...and a virus may soon be removed from the wild

The people of Liberia have earned our respect, some time for national celebrations and frankly any other rewards that may flow from denying the Makona variant of Ebola virus any hosts among their community. 

The world considered this viral species to be one of the list-toppers when it came to ranking the causes of the most scary acute infectious diseases. Ebola virus has been the basis for all sorts of 'end-of 'the-world' mutating virus horror movies, books, and TV shows. It's not at all surprising that the public view of an Ebola virus infection had long been one of blood, fear and terror.

Figure 1. The decline of the Makona variant of
Ebola virus in Guinea, Sierra Leone and Liberia
(now free of EVD transmission).
Click on image to enlarge.
Behavioural change was a major factor in reducing virus transmission in Liberia. Alongside that was a broad range of aid given from within and beyond Africa's nations. By working together, a widespread outbreak that was not initially thought likely to happen at all, was routed. 

For now. 

Liberia is not immune to new cases of Ebola virus disease (EVD) crossing its borders or popping up due to a new animal-to-human jump (a zoonosis). That could happen any day - it might be happening now. But those who are still on watch will be searching out new cases while the remaining sites of transmission - Guinea and Liberia - do their best to deny Ebola virus a chance to replicate and spread. The people of Liberia will keep watch help because they have learned very tough lessons about viruses, epidemiology and communication. At least 10,604 suspect, probable and confirmed EVD cases, 4,769 deaths and way too many stories of sadness and families destroyed are a very strict teacher. 

Figure 2. The number of confirmed EVD
cases (yellow) grinds to a standstill. Only
9 cases in the week to 10th May 2015.
Click on image to enlarge.
The crude prediction in Figure 1 suggests that zero cases across all three countries could happen at the end of May, but many stars must align for that to be a real event. 

Human factors - the causal and sustaining variables of any outbreak of infectious disease in humans and sometimes animals - remain very much in play. But once that tri-country zero case value is attained, we have 42 days of watching and waiting - from the time the final case tests negative. 

New cases may arise from sources as-yet-unknown. But even if they do keep popping up, it seems very unlikely that widespread transmission will amplify to earlier levels (see the steep slopes in Figure 2) unless a major lapse in attention occurs. Hence,the need for continued vigilance - and Liberia remains on alert for a further 90 days. That more recent figure comes about because we know that infectious Ebola virus can persist in some body sites for many weeks after signs of disease have passed. Whether that virus reservoir is present in every person and whether it actually does cause new Ebola virus infections remain unproven. When you consider what can happen when one person gets infected by an Ebola virus in a tiny remote village in a country that is ill prepared to cope with it and has traditions that lend themselves to its spread...even minor risks rightly come under more intense scrutiny.

What next for this particular virus though? The only place where the Makona variant of this member of the Zaire ebolavirus species will soon exist, is in the freezer of (hopefully) very biosecure laboratories in the US, UK, Africa, Russia, China and probably other laboratories in countries that hosted, evacuated or repatriated cases of EVD. 

There is no sign at all - and this is because of the continued efforts and focus of many currently working throughout west Africa - of the fabled "endemic Ebola" becoming a reality. Unless you mean enzootic 'Ebola'- in which case , it already is, I suspect. It seems very, very likely that the forests of west Africa continue to shelter animal hosts with less mutated versions of this and other ebolaviruses (and filoviruses and who-knows-what else). The host species and route(s) of transmission to humans are yet to be confirmed but for now, we are not too far off eradicating one unwanted viral scourge from the wild. Impressive what we can do when we pull together.