Association of influenza epidemics with global climate variability

[Sally Furniss]

Association of influenza epidemics with global climate variability

http://deepblue.lib.umich.edu/bitstream/2027.42/42662/1/10654_2004_Article_DO00002450.pdf

Ce? cile Viboud1,2, Khashayar Pakdaman, Pierre-Yves Boe? lle1, Mark L. Wilson,
Monica F. Myers, Alain-Jacques Valleron & Antoine Flahault,

Accepted in revised form 12 August 2004

Abstract.
The reasons for the seasonality and annual
changes in the impact of influenza epidemics remain
poorly understood. We investigated the covariations
between a major component of climate, namely the
El Nin? o Southern Oscillation (ENSO), and indicators
of the impact of influenza, as measured by
morbidity, excess mortality and viral subtypes collected
in France during the period 1971?2002. We
show that both the circulating subtype and the
magnitude of ENSO are associated with the impact
of influenza epidemics. Recognition of this association
could lead to better understanding of the
mechanisms of emergence of influenza epidemics.

Discussion and conclusion
In this work, we found an association between the
mortality and morbidity impact of influenza epidemics
in France and a global climate index. This
association is reinforced by the fact that it was
retrieved in two markers of influenza activity collected
independently. Previously, a separate analysis
conducted in California, USA, also evidenced an
association between ENSO oscillations and hospitalizations
for influenza and viral pneumonia [14].
Although at present no biological mechanism is
known to explain the role of climate variations in
influenza epidemics, several arguments can be
proposed. The emergence of new virus variants remains
unclear [10] and may be influenced by ENSO
oscillations. During the past inter-pandemic decade,
new epidemic variants were often first isolated in
China, which is considered as the influenza epicenter
both in pandemic and inter-pandemic periods [10,
39]. Indeed, reports establish that ENSO conditions
have a local effect over South-East Asia [13]. Moreover,
changes in local conditions may affect respiratory
virus survival and/or human indoor crowding
and in turn alter the dynamics of virus transmission
[10, 14, 40]. Strong cold ENSO phases have been
associated with lower temperature and higher
humidity in European winters [13], possibly promoting
larger and more severe influenza epidemics in
France.

 

[Anne]

Re: Association of influenza epidemics with global climate variability

than you , anne Z..

 

[wetDirt]

Re: Association of influenza epidemics with global climate variability

Actually, the connection is via bird migration and human exposure. ENSO affects climate, climate controls where the best migratory bird breeding habitat occurs year-to-year. And when migratory breeding areas overlap human farmland, particularly pig breeding areas, there is a chance to move influenza into human form.

Mallards and pintails nest near shallow ponds, and their biggest North American breeding area is in a habitat called the 'prairie pothole' area, which extends into Canada and maybe even Alaska, a region of small shallow lakes and swamps. This area is huge in wet years, and shrinks in dry years. So breeding success is tied to rainfall.

And along the way, the migration route resting areas are also tied to the area of wetlands and ponds, and in dry years with low surface areas of ponds, all the migrating birds are packed closer together, and it would then be easier to transmit multiple strains across multiple species.

So ENSO droughts drive migratory waterfowl, the influenza variability reservoir, closer together during migration, promoting development of new strains. Subsequent wet and normal years provide spreading opportunities. Note that in 1918, there was abundant spring moisture in the Great Plains, and good year for the duck population. Note also that the first outbreak was in pigs, and in the Prairie Pothole region. Hmmmmmmm.

Now I note that H5N1 showed up at Chaney Lake in a drought year, and that we have had a series of droughts since then. There has not been a really good duck season in North America since this whole thing started. But what will happen if we get a whopper El Nino? The midwest, a big pig-raising area, will have a huge duck season too. Perfect storm.