Published Date: 2010-08-24 19:00:04
Subject: PRO/AH> Encephalitis - Greece (10): (MC) WNV, comment
Archive Number: 20100824.2972
ENCEPHALITIS - GREECE (10): (CENTRAL MACEDONIA) WEST NILE VIRUS, COMMENT
A ProMED-mail post
ProMED-mail is a program of the
International Society for Infectious Diseases
Date: Tue 24 Aug 2010
From: Paul Reiter [edited]
In a recent ProMED commentary on the WNV [West Nile virus] outbreak
in Greece, the moderator remarked that there had not been any reports
of large scale mortality in birds.
Mortality in birds has rarely been reported in Europe. The Austrians
and Hungarians have seen some -- most strikingly in falcons used in
falconry -- but in other regions it is probably rare.
In Romania, seroprevalence in the Bucharest area is consistently
high, but scientists at the Cantacuzino Institute who have worked on
the virus in the field for several decades have not observed any
Professional ornithologists in the Danube Delta who have worked with
the EU-funded EDEN-West Nile project for more than 5 years have not
reported any mass mortality although seroprevalence is high. None of
the other partners on the project (in Spain, France, Italy and Czech
Republic) have reported mortality in birds.
A recent serosurvey of horses in a large area in eastern Romania
(also associated with the EDEN project), approximately 30 percent
were seropositve but there are no reports of clinical cases, yet the
horse population of the country is estimated at about 750 000.
Similarly, in a survey in Senegal, seroprevalence in horses was
age-related, climbing to above 90 percent in 7-year old horses;
clearly there is a consistently high rate of transmission, yet
clinical cases appear to be unknown.
By contrast, in some parts of Europe clinical cases in horses are a
sensitive indicator of local transmission, just as in the New
World. These are regions where WNV transmission is probably much
lower and more erratic. Thus it would appear that some form of
innate immunity is present in horses in areas of the Old World where
transmission is common.
Such innate immunity would appear widespread among European birds,
both resident and migratory, and in the New World in species of bird
introduced from Europe (e.g., House Sparrow, Starling and Rock Dove).
Paul Reiter, PhD, FRES
Unite "Insectes et Maladies Infectieuses"
25-28 rue du Dr Roux
[ProMED thanks Dr. Reiter for his interesting comments. Host
resistance of birds and horses in areas of frequent West Nile (WN)
virus transmission, as D. Reiter suggests for eastern Europe, is a
plausible explanation for absence of wild bird and equine mortality
there. One also wonders if there are differences in virulence of the
strains of WN virus circulating in Europe versus those circulating in
It would be interesting to know if WN virus strains from the Americas
would cause mortality in native eastern European birds, especially
corvids (experiments that probably will never be done). Also, it
would be interesting to know if eastern European birds infected with
local WN virus strains develop viremias of sufficient duration and
magnitude to infect local _Culex_ mosquito vectors, in the absence of
clinical disease. - Mod.TY]