Egypt: Investigation Continues After Wild Poliovirus Is Detected

A child is vaccinated in Nigeria where polio is still endemic.
27 January 2013

Washington, DC — Nearly eight years after the World Health Organization declared Egypt polio free and two years after the last reported case, wild poliovirus has popped up in the capital, Cairo, after routine testing of the city's sewers. Health authorities suspect the virus originated in Pakistan.

But finding polio is sewer water is not an immediate red flag, according to Steve Oberste, viral division laboratory chief at the U.S. Centers for Disease Control and Prevention (CDC). The polio vaccine used in Egypt relies on weakened polio strains, which are then excreted - hence their presence in wastewater. But in this case, the samples were wild, or naturally occurring.

So far the Egyptian government has not identified any cases tied to the recent polio find. But Oberste said continued vigilance in imperative and ongoing. Children who have not been immunized could become infected, and then the disease could spread. Bearing that in mind, Egypt has teamed up with WHO, UNICEF and the CDC to step up surveillance for virus strains and to launch an emergency vaccination campaign.

The CDC says three regions of the world are certified as polio free – Europe, the Americas and the Western Pacific. There are only three polio-endemic countries in the world: Afghanistan, Pakistan and Nigeria.

These nations have never interrupted the transmission of wild poliovirus.

AllAfrica's Lauren Everitt recently caught up with Oberste, whose team helped confirm the identity of the wild Egyptian strains, to learn more about the implications of the recent discovery.

Could you explain the background of the recent polio discovery in Egypt? Is this something that health authorities and the Egyptian government should be concerned about?

Polio was found in two environmental samples at two sites in greater Cairo. There's ongoing environmental surveillance as a supplement to the general surveillance, and that has been going on for 10 to 15 years in Egypt at a number of sites.

The samples are processed at the Egyptian National Polio lab there in Cairo. If they have something that seems to be of concern or needs further characterization, they send it to us at the CDC.

So there were some samples that they had flagged as being concerning and they sent them to us. Last week we confirmed their results and did genetic sequencing showing the samples were, in fact, wild virus that was mostly closely related to virus that had been found in Pakistan.

The concern is that Egypt has been polio free for a number of years - I think since 2004. So it's a potential importation. There's a concern that it could spread within the community. That's really why this is news to begin with. They've actually had a previous virus importation that was also discovered in sewage in 2010 and that virus came from Sudan. But it was not linked to any cases either, fortunately.

What are the implications of this most recent discovery?

Well the virus gets around and people travel extensively. One of the biggest outbreaks was seeded by Nigeria a few years ago and went all over West Africa. There were lots of cases associated with the Nigerian virus.

So the real implication is making sure that people, children, in the community, are properly immunized. If they're immunized, they may actually get infected but they won't become diseased.

So the hope is that the immunization levels in Egypt and greater Cairo are high enough that there won't be any disease. That's also part of what the teams are doing is checking immunization records. They're looking at their previous vaccine campaign records to make sure they've properly covered these areas and planning some supplementary immunization activities that will target as many as 3 million children.

What are the next steps in ensuring that the polio threat is contained?

Polio is kind of interesting in that the vast majority of infections do not actually result in paralysis. Only about one out of every 100 infected individuals will become paralyzed.

So the attack rate is actually quite low. That means it could just be someone who is infected is carrying the virus. They could possibly live in Pakistan and traveled to Egypt or they could be an Egyptian who went to Pakistan. The virus can be excreted in the stool of an infected person for several weeks. Being excreted it ends up in the sewage.

So far there is no known paralyzed person and so part of the response has been for the government of Egypt and some of the partners, such as the World Health Organization, to launch a response, which they did quite quickly.

Could you elaborate on the Egyptian government's response?

We identified the virus last Friday (January 18) and they had a response started on Monday (January 21). They've sent teams to the two areas where samples were taken, and they're doing an active search for cases.

There's normally a surveillance system that identifies cases of Acute Flaccid Paralysis, or AFP, and that's the hallmark of polio. There are a number of other things that can cause AFP so it's not a strict definition, but it's a way to flag potential polio cases. Normally those are reported to the ministry and investigated. However, that depends on someone going to a clinic or going to a hospital, taking a child to a physician to be checked and having that reported. But no system is perfect, so they're going to clinics and looking at places that might have a paralyzed case and talking to physicians and just seeing if there are any recent cases that would be compatible with a polio infection.

The response is ongoing. So far they seem to be really on top of things.

What challenges will the Egyptian government face during the vaccination campaign?

A lot of these kinds of thing occur in slum areas that are very poor with poor sanitation. They are overcrowded areas so it's difficult to reach all the families. So being able to reach all the families and cover the area is difficult.

There were some areas that were difficult to reach in the previous campaigns because of the political and insecurity issues that have been ongoing in Egypt. In the last couple of years they've had what they call National Immunization Days where teams go out and try to immunize as many children under age five as they possibly can. Often those include house-to-house campaigns, literally going from one house to the next to look for young children and make sure they're immunized.

But they couldn't do those house-to-house campaigns in a lot of areas because of the political instability and some areas just aren't very secure or safe for the vaccinators to go. We've seen that illustrated in Pakistan in the last month where a number of polio workers were killed.

As you say, vaccination workers have been targeted in Pakistan. Are there any concerns that the same could happen in Egypt? What about the recent political protests?

I don't think vaccination workers are being targeted. I think any time there's any kind of protest and unrest you worry a little bit that things can spill over, but I don't think there are any concerns that they're being targeted specifically. Egypt has actually been quite good about immunizing, and there don't seem to be any real problems with people refusing vaccinations, at least not in the same way as in Pakistan.

What is the risk of a polio resurgence in Cairo?

There are no known cases at this point. It's only samples from these two sites, so it's not being found all over Cairo. They've increased the frequency of sampling at these sites, and we're working with the Egyptian laboratories to carefully assess their other specimens to make sure there's nothing that has been missed. So far there's not, which is good. So it seems to be localized so far.

It could simply be one family with a number of children or one person who moves around a little and is in two different places, maybe traveling between where they live and where they work.

The real concern is that if there are unimmunized children in the area, then it could take hold. That's the reason for the strong response and finding out what the immunity levels are, making sure that there's coverage and adding some supplementary immunizations to ensure the immunity level stays high.

Have there been any clues as to how the poliovirus got into the sewer?

There's nothing at this point. So they're certainly investigating to see if there has been any travel, people known to be traveling between the two countries, recent immigrants. I think at this point they don't have any additional information.

Presumably, it would have been an infected person who came in and was excreting virus in their feces and it got into the sewer.

Has there been a polio scare similar to this in recent history?

In December of 2010 in Egypt there was a strain that had come from Sudan. I believe that's the only instance, or the only one I can think of, for a wild virus being found elsewhere in sewage, particularly.

However, there was a small outbreak in China in 2011 that was also traced back to a virus from Pakistan. Two of the cases died in southwestern China so not too far from the Pakistan border. It turned out that the virus had come from the southeastern part of Pakistan.

Your team at the CDC confirmed the Cairo test?

The Egyptian laboratory identified polio. But you have to remember that the virus that's used for immunizations is a live vaccine, and so that's excreted as well. The vast majority of samples that they detect in the sewage are vaccine virus with no serious concerns - it's the same as what's in the vaccine. But they identified a virus that had properties that were not totally vaccine-like and so that was the flag that signaled them to send it to us.

They sent it to us and asked us to urgently look into it. We confirmed their results and did genetic sequencing and then confirmed that it was in fact wild virus.

Could you break down how the genetic sequencing works and why it's used?

A virus has genetic material just like we do. The poliovirus changes very rapidly and so you can use that as kind of a fingerprint. Using the same technology that's used for the human genome project, we can actually tune into this fingerprint of the virus and determine a small, small piece of it. From that we can actually tell where it came from.

Any final thoughts on the poliovirus find in Egypt?

This puts a little extra pressure on Pakistan. If they're exporting their virus to their neighbors, that's more impetus to stamp out the virus there. Currently they're in the low season. These kind of viruses have a little bit of a seasonality and in the warmer months they tend to transmit more than in the colder months. Of course, it's quite cold in Pakistan right now so this is kind of an opportunity to really stop transmission in the country. There have been very few cases in the last couple of months, again because it's the low season, and so if we can strike now there's actually an opportunity to interrupt transmission in Pakistan.

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