virology blog
About viruses and viral disease
Vincent travels to the European Congress of Virology in Rotterdam and with local co-host Marion Koopmans speaks with Martin Beer, Stephan Gunther, and Vera Ross about their careers and their work on Lassa virus, Borna virus, and insect viruses.
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Show notes at microbe.tv/twiv
I cannot let September pass without noting that 34 years ago this month, I arrived at Columbia University to start my laboratory to do research on poliovirus (pictured). That virus is no longer the sole object of our attention – we are wrapping up some work on poliovirus and our attention has shifted elsewhere. But this is a good month to think about the status of the poliovirus eradication effort.
So far this year 26 cases of poliomyelitis have been recorded – 23 caused by wild type virus, and three caused by vaccine-derived virus. At the same time in 2015 there were 44 reported cases of polio – small progress, but, in the words of Bill Gates, the last one percent is the hardest.
One of the disappointments this year is Nigeria. It was on the verge of being polio-free for one year – the last case of type 1 poliovirus in Nigeria had been recorded in July of 2014. In August the government reported that 2 children developed polio in the Borno State. The genome sequence of the virus revealed that it had been circulating undetected in this region since 2011. Due to threats from militant extremists, it has not been possible for vaccination teams to properly cover this area, and surveillance for polioviruses has also been inefficient. The virus can circulate freely in a poorly immunized population, and as only 1% of infections lead to paralysis, cases of polio might have been missed.
The conclusion from this incident is that the declaration that poliovirus is no longer present in any region is only as good as the surveillance for the virus, which can never be perfect as all sources of infection cannot be covered.
Of the 26 cases of polio recorded so far in 2016, most have been in Afghanistan and Pakistan (9 and 14, respectively). It is quite clear that conflict has prevented vaccination teams from immunizing the population: in Pakistan, militants have attacked polio teams during vaccination campaigns.
Recently 5 of 27 sewage samples taken from different parts of the province of Balochistan in Pakistan have tested positive for poliovirus. Nucleotide sequence analysis revealed that the viruses originated in Afghanistan. The fact that such viruses are present in sewage means that there are still individuals without intestinal immunity to poliovirus in these regions. In response to this finding, a massive polio immunization campaign was planned for the end of September in Pakistan. This effort would involve 6000 teams to reach 2.4 million children. Apparently police will be deployed to protect immunization teams (source: ProMedMail).
The success of the polio eradication program so far has made it clear that if vaccines can be deployed, circulation of the virus can be curtailed. If immunization could proceed unfettered, I suspect the virus would be gone in five years. But can anyone predict whether it will be possible to curtail the violence in Pakistan, Afghanistan, and Nigeria that has limited polio vaccination efforts?
Polio returns to Nigeria, Zika virus spreads in Miami, and virus infection of plants attracts bumblebees for pollination, from the virus gentlepeople at TWiV.
You can find TWiV #400 at microbe.tv/twiv, or listen below.
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I have a soft spot in my heart for Lassa virus: a non-fictional account of its discovery in Africa in 1969 inspired me to become a virologist. Hence papers on this virus always catch my attention, such as one describing its origin and evolution.
Lassa virus, a member of the Arenavirus family, is very different from Ebolavirus (a filovirus), but both are zoonotic pathogens that may cause hemorrhagic fever. It is responsible for tens of thousands of hospitalizations, and thousands of deaths each year, mainly in Sierra Leone, Guinea, Liberia, and Nigeria. Most human Lassa virus outbreaks are caused by multiple exposures to urine or feces from the multimammate mouse, Mastomys natalensis, which is the reservoir of the virus in nature. In contrast, outbreaks of Ebolavirus infection typically originate with a crossover from an animal reservoir, followed by human to human transmission. Despite being studied for nearly 50 years, until recently the nucleotide sequences of only 12 Lassa virus genomes had been determined.
To remedy this lack of Lassa virus genome information, the authors collected clinical samples from patients in Sierra Leone and Nigeria between 2008 and 2013. From these and other sources they determined the sequences of 183 Lassa virus genomes from humans, 11 viral genomes from M. natalensis, and two viral genomes from laboratory stocks. All the data are publicly available at NCBI. Analysis of the data lead to the following conclusions:
Perhaps the most important result from this work is the establishment of laboratories in Sierra Leone and Nigeria that can safely collect and process samples from patients infected with Lassa virus, a BSL-4 pathogen.
On episode #348 of the science show This Week in Virology, Vincent and Rich discuss fruit fly viruses, one year without polio in Nigeria, and a permissive Marek’s disease viral vaccine that allows transmission of virulent viruses.
You can find TWiV #348 at www.microbe.tv/twiv.
A new bivalent poliovirus vaccine, consisting of infectious, attenuated type 1 and type 3 strains, has been deployed in Afghanistan. The use of this vaccine was recommended by the Advisory Committee on Poliomyelitis Eradication, the global technical advisory body of the Global Polio Eradication Initiative. Considering the polio experience in Nigeria, the elimination of type 2 poliovirus from the vaccine might have serious consequences.
There are three serotypes of poliovirus, all of which can cause poliomyelitis. Infection with one serotype of the virus does not confer protection against the other two; therefore poliovirus vaccines have always included all three serotypes (they are trivalent). The attenuated vaccine that is used in the eradication effort is an infectious vaccine. The vaccine is ingested, the viruses replicate in the intestine, and immunity develops. Viruses of all three serotypes undergo genetic changes during replication in the alimentary tract. As a consequence, the vaccine recipient excretes polioviruses that can cause paralysis. These so-called vaccine-derived polioviruses (VDPV) can cause outbreaks of poliomyelitis in non-immune people, as described in Polio among the Amish.
Poliovirus type 2 was declared eradicated from the globe by the World Health Organization in 1999. When type 2 poliovirus was eliminated, many countries began using monovalent type 1 and type 3 vaccines: one vaccine for type 1 and another for type 3. As a consequence of this immunization strategy, population immunity to type 2 poliovirus declined. Not unexpectedly, there was an outbreak of type 2 poliovirus in Nigeria in 2006. The surprise was that the outbreak was caused by a poliovirus type 2 vaccine strain.
Before 2003, the year that Nigeria began a boycott of polio immunization, the trivalent polio vaccine was used. Immunization resumed with monovalent types 1 and 3 vaccine in 2004. Therefore the source of the VDPV type 2 is most likely the trivalent vaccine used before 2003.
The press release at polioeradication.org announcing the bivalent vaccine proclaims:
Of the three wild polioviruses (known as types 1, 2 and 3), type 2 has not been seen anywhere in the world since 1999.
The statement ignores the fact that there is vaccine-derived type 2 poliovirus in the world – and it can cause polio as well as ‘wild’ poliovirus. Such strains have been isolated in Nigeria as recently as October 2009. Why isn’t the type 2 vaccine being used in Afghanistan when it is very likely that vaccine-derived type 2 poliovirus is still circulating? Just because we haven’t isolated type 2 poliovirus recently doesn’t mean that it’s gone. No type 2 poliomyelitis was detected in 1999, yet the vaccine-derived virus was silently circulating in humans.
What will be the WHO response to an outbreak of type 2 polio in Afghanistan? They will probably deploy trivalent vaccine, as was done in Nigeria in 2006. But this approach will simply lead to another cycle of eradication and emergence of type 2 polio. It’s time to begin using inactivated poliovirus vaccine, which I’ve been dreaming about for some time.