The major vector-borne surveillance techniques
we've talked about are: pathogens surveillance,
vector surveillance, amplification, and reservoir hosts surveillance.
The fourth is secondary host surveillance.
Remember that secondary hosts for these viruses,
especially West Nile, Eastern equine encephalitis,
and St. Louis encephalitis secondary hosts are primarily humans,
but for West Nile virus and Eastern equine encephalitis virus,
secondary hosts are also horses.
We can use host serology and host mortality as a surveillance measure of
the number of infected mosquitoes that are
present and transmitting and with secondary hosts surveillance,
there are a couple of ways to measure the involvement of
secondary hosts in the transmission of these viruses.
Human surveillance, the presence of a human case is
an excellent indicator that a virus is being transmitted.
Of course, one of the things we want to do is avoid human cases.
We don't want human cases to be the primary indicator of virus transmission.
We want to know way ahead of time that humans are at risk and prevent human cases.
But, a lot of times
human cases are the first indicator that virus transmission is occurring.
The second indicator is secondary hosts surveillance and
Eastern equine encephalitis and West Nile virus,
horses are the primary secondary host.
Emus are wild pet birds are also
secondary hosts that may indicate
the presence of virus transmission and with those secondary hosts,
host death and then virus detection after-death
is a primary way of indicating the presence of virus transmission.