Question-Hanta Virus Status

[Heikki Henttonen]

In article <4dmfk1$kr8 at news.mcn.net>, d hayman <hayman at mcn.net> says:
>
>I am interested in learning of the current status and epidemiology
>of the hanta virus.  My area had two fatalities several years ago
>but there have been no subsequent re-occurences.
>
>Is there any evidence suggesting the agent is restricted to warmer areas?

The question includes a misunderstanding. There is a number of different
hantaviruses, not only the well known Sin Nombre you obviously refer to. 
Hantaviruses are rather host specific, or occur in a group of closely
related host species. There are some 2000 species of rodents; let's wait
and see how many  "species" of hantaviruses we know after some years. And
all in the insectivores etc added. The occurrence of specific hantaviruses
must therefore be related to the number and geographic ranges of potential 
host species. In this respect, it would seem that more hantaviruses
will be found where the number of host taxons is higher, e.g. the tropics.
On the other hand, hantavirus antibodies have been found also in arctic 
lemmings, so... Within a host species (I think you questions addresses to 
this), the occurrence of a specific hantavirus seems the depend on the 
population dynamics oh host species. The essential feature is that the 
transmission threshold for the spread and maintenance of a virus is 
exceeded. Depending on the dynamics of the host, virus can occur regularly 
in cycles or irregularly at long-term intervals, or anything between. And
there are great differences in the dynamics of rodents between the species
as well as geographically within a species.

Thinking about the number of rodent (and other mammal)  species and their 
abundances, I would like to guess that there are more hantavirus "species" 
at low latitudes, but those occurring at higher latitudes are more 
prevalent. But so far this is only my educated speculation.


>Could the virus, after initial introduction, have failed to establish a long term
>reservior or perhaps was unable to maintain the reservior?  I realize of course 
>that several years without disease is not evidence of either conjecture.

Your virus was hardly "introduced", but has most probably remained in the 
area from the far history as long as the rodent hosts. 

>Our area,(northern Montana plains) has a significant amount of grain milling,
>and it was my feeling that the virus originally arrived from infected mice via 
>rail and the grain shipments. Subsequent CDC investigation relating to the fatalities
>was inconclusive, at least that which was reported to the public.  One of the 
>fatalities was an employee of a mill.  The investigation did establish the virus 
>occurring in local mouse populations, 

See above. 

though I do not recall
>the tests used to confirm the isolation.
>
>
>Thankyou for sources and/or information.
> 

----
Heikki Henttonen
Finnish Forest Research Institute
POB 18, FIN-01301 Vantaa
Finland
phone  358-0-85705477
fax       358-0-8572575
e-mail   Heikki.Henttonen at metla.fi