By Jonas Waldenström
Unlike most organisms, viruses are often named after the site they were first found. Sometimes these names give a flare of dark jungles, full of mosquitoes, and the eyes of unknown animals that stare at you in the dark. Surely, the name Ebola is enough to spark fears in any man. This virus, named after a river in Congo, is one of the ugliest viruses we know of: a hemorrhagic fever virus where you literally bleed to death. I think of the Heart of Darkness, that dark Joseph Conrad novel. It makes me shiver, every time. A related virus is Marburg virus, named after a city in Germany where a laboratory worker accidently infected himself and caused the first human case. Although from Germany and not a deep African jungle, a Marburg virus still sounds like a vicious killer, especially if said with a thick German accent.
Another favorite is the chikungunya virus. I can’t decide whether it is the name of a fluffy rabbit, or something very deadly. Mixed feelings for that name. The virus is pretty bad though. A mosquito borne illness first discovered in Tanzania, but which name does not denote the place of origin, but the local name for “that which bends up“. That prosaic word stems from the contorted posture of patients suffering joint pain and arthritic symptoms. However, although interesting (read: horrific) diseases, neither Ebola, nor Chikungunya virus are to be found in Mallards – my pet model species. But there is a city virus that does infect Mallards: Newcastle disease virus!
This week in the Virology Journal we published an article on the occurrence of Newcastle disease virus in Mallards sampled at Ottenby. Newcastle disease virus, or NDV for short, should not be mistaken for Newcastle Brown Ale. The latter is a pretty nice beer, the former an infectious disease of birds. In fact, NDV – or avian paramyxovirus type 1 which it is also called – can be a devastating disease in poultry. It is fairly rare in Northern Europe, but occasionally there are outbreaks in poultry. To complicate matters even more, there are three different classes, or pathotypes, of NDV depending on their severity of infection. Lentogenic viruses are fairly benign, and are not associated with severe disease, while mesogenic and velogenic strains are real killers. The difference between the pathotypes is related to genetic differences in the F protein of the virus, a key player in the fusion of the virus with the host cell. In order to infect the cell, the F protein must be cleaved by host proteases at the F0 cleavage site, and velogenic strains can be cleaved by many more types of proteases than lentogenic strains thereby causing a more systemic, less local, disease.
So what did we do? Given that outbreaks are rare in Sweden, and occur mainly in late autumn, we wanted to know how prevalent NDV was in our Mallard population and whether this species could be involved in transmission. We screened roughly 2300 samples collected from migratory Mallards for the presence of NDV RNA. A molecular typing method is like a fishing expedition: you need to have the right equipment and the right bait to get the fish. Or, in our case, positive amplification of NDV RNA of the F gene in real-time-PCR assays. It took a lot of time and effort to optimize the protocols.
And what did we find? Twenty of the samples, some from the same individuals sampled more than once, were positive for NDV. This makes NDV pretty rare in Mallards, at least compared to influenza A virus that can be found in a prevalence of 10-30% at Ottenby in autumn. I had expected to see more infections, and the NDV was one of the viruses I had thought to include in coming viral pathogen assemblage studies. At the moment it feels a bit to rare to work efficiently with, but we will see. Paramyxoviruses are interesting and besides the NDV there is nearly two handfuls of other avian paramyxoviruses to screen for. The phylogenetic analysis, and the sequencing of the F cleavage site placed the Mallard viruses in the lentogenic group. And the risk for poultry from the Mallard viruses should be negligible.
It is always nice to get a paper out. In the old days you could actually feel the glossy paper between your fingers – those days are more or less gone, with online-only and printed pdf. But it still feels good. And it feels even better today, after a few pints of microbrewery beer in Aberdeen – this is the closest I have been to Newcastle in years!
The full paper: Tolf, C., Wille, M., Haidar, A-K., Avril, A., Zohari, S. & Waldenström, J. 2013. Prevalence of avian paramyxovirus type 1 in Mallards during autumn migration in the western Baltic Sea region. Virology Journal 10:285.