Dengue

Recently I asked readers to identify errors in an animation of influenza virus replication. I am impressed with the number of good responses posted in the comments section. Here is a synopsis of the errors (there is more than one).

1. Influenza virus is released from cells by budding, not when the cells burst, as is shown in the animation.

2. Influenza virus is not the only virus capable of antigenic shift.

3. There isn’t any mucus on the epithelium. It should be there.

4. One problem is that the animation describes the production of a mutant virus, but it shows reassortment. The two are not the same. More importantly, the animation illustrates co-infection of cells with a human strain and a swine/avian strain. The implication is that this gave rise to ‘mutated’ viruses which then infected people.

We don’t know how the new virus emerged yet, but here is one scenario. Over ten years ago, pigs that were infected with swine influenza were then infected with avian, and then human influenza viruses. A variety of recombinants emerged which propagated globally in pigs and occasionally infected humans. More recently, swine influenza virus genes from Eurasian and North American pigs mixed. Finally, a human was infected with this pig virus and one virus emerged which was able to transmit. Presumably this virus differs from what was in the pig by a number of base changes which enables the virus to spread among humans.

5. The epithelium is probably incorrect, as pointed out by several readers. It certainly doesn’t look like any respiratory epithelium I’ve seen under a microscope. Some readers had questions about this, but since I’m not an expert on the respiratory epithelium, I’ll refrain from specific criticism.

6. “The current flu in circulation is an entirely new, mutated pathogen…” The virus is not entirely new – it is very similar to what has been circulating in pigs for many years. What is new is the combination of influenza RNA sequences from Eurasian and North American pigs.

The rest of the statement – “formed from elements from human, pig, and avian virus strains” – implies that this combination occurred recently, as does the animation (#4). But this combination occurred over 10 years ago and since then the virus has been circulating in pigs.

7. The last sentence – “Overflowing with mutated viruses, the pig’s respiratory epithelial host cells eventually burst open and circulate the new flu virus into the susceptible human population”. The implication is that reassortment has lead to the production of many ‘mutated’ viruses. Incorrect, as discussed in #4. But it’s true that virus replication always leads to the production of a collection of mutant viruses – or more accurately, viral variants. A human was infected with such a collection of influenza virus mutants; one mutant replicated and transmitted and this is the virus we are seeing today. If this doesn’t make much sense, be patient until we discuss the quasispecies concept.

Perhaps one reader best summarized this animation:

“Nothing useful there….More mis-information…Was there anything remotely accurate?”

If you are wondering why I even bothered to direct you to this video, the answer is that understanding errors is always a learning experience. In my virology class we often discuss ‘flawed’ research papers for this reason.

Movie-makers often get their science wrong, especially when dealing with viruses. The movie Resident Evil and its sequels is an example. But animations produced for educational purposes should be much better than this. Here is a good animation of dengue virus entry into cells: