[leps-talk] Non-avian vectors and rapid spread of WNV

[Anne Kilmer]

To what degree could people be a vector? Their movements seem to be 
appropriate. Has anyone established that we do *not* carry and spread 
the virus, infecting mosquitoes wherever we go?
How long after contracting the disease might a human carrier be "hot"?
as to your butterfly theory, how would the disease get from the 
butterfly to the mosquito? Seems rather far-fetched, to me.

Anne Kilmer
Mayo, Ireland

Michael Gochfeld wrote:
> Bob Augustine (see below) provided an innovative suggestion of how a
> non-avian vector (particularly Pieris rapae) might account for the
> spread of WNV.
> I think it is important to think creatively about West Nile ecology and
> to recognize that the most interesting aspects lie outside of humans. 
> 
> I have believed that the gap in our knowledge of "rapid spread" may
> represent a lag between the time the virus arrives and begins to
> multiply in local avian reservoirs, and the time it is "discovered" due
> to either avian, equine, or human morbidity or mortality. 
> 
> Thus the rapid spread may be an artifact of our sampling and monitoring
> programs.  
> 
> As author of a book on Butterflies of New Jersey, and as an observer on
> the current Cabbage Butterfly population explosion (late July 2003) in
> central NJ, I have more than a passing interest in the Augustine
> proposal. I will also circulate it to the two lepidoptera list servers I
> subscribe to and see if there are other perspectives. 
> 
> I am grateful to Bob for pointing out the Walker paper on butterfly
> migration at Gainesville, FL.  It points to a net northward movement of
> Cabbage Butterflies in spring AT THAT SITE.   In New Jersey we do not
> think of Cabbage White's as particularly migratory (either north or
> south), BUT I WILL ASK THE LIST MEMBERS WHAT HAPPENS AT OTHER
> LOCALITIES.  
> 
> Also quite a few butterflies feed on bird droppings, BUT I CAN'T RECALL
> SEEING A CABBAGE WHITE AT BIRD DROPPINGS.  PERHAPS OTHER LIST MEMBERS
> HAVE A DIFFERENT EXPERIENCE. 
> 
> Most of the other migratory butterflies irrupt from the southwest or
> south into the northeast, which doesn't seem the right direction.  The
> Monarch, of course, has dramatic southward and westward migrations in
> Sept-Oct, which would be the right time to carry a virus from the index
> cases in the northeast----but I don't recall ever seeing a Monarch at
> bird droppings.  I'll post that question also. 
> 
> Dragonflies, now there's a thought.  Lots of good southward migrant
> species and mosquito eaters. 
> 
> Michael Gochfeld
> 
> 
> 
> 
> Bob Augustine wrote:
> 
>>A proposed new WNV vector (and other WNV observations)
>>
>>In a previous (unanswered) e-mail I suggested that we need to find another vector that travels en-
>>masse, south to north, in June or July to explain 2002's rapid extension of WNV concentration
>>from the Gulf coast to the upper Midwest. Since bird movements do not match this pattern, I
>>further suggested that dragonflies, butterflies, or moths might.
>>
>>Only a few butterfly species are known to migrate at all, but more are coming to light. In recent
>>correspondence, an article published in 2001* revealed that the (imported) Cabbage White, Pieris
>>rapae, (said by some to now be the most abundant butterfly in North America) sometimes has a
>>very marked late spring eruption northward. Recent postings on Internet listservs from PA and NJ
>>report unusually high numbers of this species this year. Its association with cabbage-also a food
>>plant of the Fall Army Worm, Spodoptera frugiperda, noted as having invaded Ontario from MS
>>in September 1973-and this migratory pattern (most evident in the record from 1987) lead me to
>>propose the Cabbage White as a potential WNV vector. I don't think mosquitoes bite butterflies
>>or caterpillars, however, these butterflies are known to extract minerals from bird droppings,
>>which may be the way they pick up the virus (if they do).
>>
>>I urge the CDC to investigate the Cabbage White as a possible West Nile Virus vector, as well as
>>other insect pests of cruciferous plants with northward summer movements.
>>
>>Another dot to connect in this mystery just surfaced in a posting from NJ. As you may know,
>>catnip has been found to be 10 times as effective as a mosquito repellent as DEET. Catnip is not
>>only among the plants Cabbage Whites are reported to be feeding on in NJ, the poster
>>writes,"First thing in the morning the cabbages congregate on catnip, even in the shade."
>>
>>I also wrote earlier that the CDC maps for 2002 offered no clues as to geographical routes of
>>transmission. In the 2003 bird map, however, there is a marked tendency for positives to cluster
>>along river valleys. This may simply be because humans concentrate in such areas and are thus
>>more likely to find dead birds there. On the other hand, I think the pattern is a bit too extensive to
>>be explained this way. If there is a corridor effect, I reiterate that bird numbers (post-breeding
>>wanderers-egrets, herons etc.) are too few to support a bird vector hypothesis. But butterflies
>>that migrate north in summer in larger numbers are also noted for taking river valley routes in
>>doing so. If moths behave in a similar fashion, they could also account for this pattern, flying
>>undetected at night.
>>
>>It is interesting to observe that so far in 2003 the largest number of human WNV cases (36) is in
>>CO, not IL, LA,MS or the other places that were focal points of the last 2 years. It almost
>>appears that the disease is waning in those areas now. Perhaps immunity develops in humans in
>>only a couple of years as it seems to have in birds in the East (and perhaps in Europe). This would
>>be really good news.
>>
>>The spread pattern on the bird map would be easier to see if more counties did testing. This year
>>it seems fewer have along the corridors than last year. The white (untested) areas have to be
>>ignored and only the green (tested) regions provide a useful context for the positive test results.
>>
>>*Butterfly Migrations in Florida: Seasonal Patterns and Long-Term Changes, Thomas J. Walker,
>>U. Fla., Gainesville, Environ. Entomol. 30(6): 1052-1060 (2001)
>>http://esa.edoc.com/environ/v30n6/v30n6p1052.pdf
>>
>>Bob Augustine
>>raugustine at tms-hq.com
>>Rockville, MD
> 
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