Back to the West Nile Virus listserv archive.

Excerpts below from recent postings on the ProMED mail listserv about birds and WNV; most in response to the USGS news release late last week that West Nile Virus can be transmitted bird-to-bird, in absence of mosquito bites:

[1]
Date: Fri, 27 Oct 2000
From: Dr. Hugh Whitney (HughWhitney@mail.gov.nf.ca)
Director, Animal Health Division, NF Dept. of Forest Resources & Agrifoods, P. O. Box 7400, St. John's, NF A1E 3Y5

Regarding the study on crows kept in confinement, considering how heavily parasitised wild birds can be, was it considered that there may have been a variety of ectoparasites feeding off the infected birds which then crawled onto and infected the uninfected birds?

[2]
Date: Fri, 27 Oct 2000
From: Tracy L. Middleton DVM, Captain, USAF, BSC 437 MDG/SGP (MIDDLET@charleston.af.mil)
Public Health Flight, Deputy Commander, Charleston AFB, SC

...Were the birds treated for external biting insects/parasites prior to being place in the aviary together? What was done to guarantee that the aviary was biting insect/parasite free?

[3] Date: Fri, 27 Oct 2000
From: DesertWoodrat@aol.com>

Being a wildlife rehabilitator, [I am aware that] the bonded pairs [of many species of birds} preen each other and often exchange food from their crops with each other. I am guessing that if the virus is in all their organs, it is probably also in their saliva. Also, if birds step in another infected birds feces, and later scratch themselves and deposit the virus on their feathers, they will ingest the virus when they preen. The virus [may] also probably be passed from parent to offspring during the spring and summer.

One other thought about bird-to-bird transmission of West Nile Virus. Have other insect vectors been looked into besides mosquitoes? There are other sucking/biting insects on birds that could spread the disease between the birds. Some of these insects may also bite humans, many only bother birds. Maybe you could check the parasites/insects found on already infected birds and see if any of these insects also carry the virus, if you haven't already.

[4]
Date: Mon, 23 Oct 2000
From: Marcus Hutka - PHSX, Maricopa County Dept. of Public Health (marcushutka@mail.maricopa.gov)

Is anyone conducting surveillance of bird populations on wintering grounds for the presence of WNV? It would seem that as birds migrating from the Pacific, Central, Mississippi, and Atlantic fly ways converge on common wintering grounds, WNV will propagate in the populations, allowing the birds to carry WNV back to their respective summer grounds. If this is the case, shouldn't we be preparing for a much more widely disseminated threat next summer?

[5]
Date: Fri, 27 Oct 2000 From: Kirk Greenway, MA, MPH, Suburban Maryland, USA (captainnemo1@yahoo.com)

I was wondering if, given the possibility of droplet transmission of WNV, removing bird houses and bird feeders in areas where WNV is spreading might slow spread of the virus. How would this hypothesis be tested? I would suggest some kind of dacron tipped swab of bird-feeders and bird house enclosures under use collected immediately into heat stable medium. If a WNV PCR or LCR technique exists, this could reliably test for presence in a sample of approximately 250 in an area where transmission is underway such as NJ, NY, or Eastern Canada. Have any viral persistence of WNV studies been documented?

[6]
From: ProMED Moderator

[Perhaps those concerned in the experiments demonstrating bird-to-bird transmission can provide some answers? The importance of the original observations is surely that virus can pass directly between birds without the intervention of a mosquito vector; the precise mechanism is less relevant at this stage. - Mod.CP]

[7]
Date: Fri, 27 Oct 2000 From: Omar Shafey (oshafey@karnak.com)
Source: Ha'aretz, filed 27 Oct 2000 [edited, byline: Avi Shmoul] http://www3.haaretz.co.il/eng/scripts/article.asp?mador=14&datee=10/27/00&id [URL Invalid; page not posted]

Pigeons Identified As Source Of West Nile Virus In Israeli Kibbutz: Kibbutz Kabri, in the north of [Israel], has begun destroying its pigeons, after the birds were found to be carrying West Nile virus. This is the first time the virus has been discovered in pigeons. Until now, the only birds known to carry the virus [in Israel] were geese. The Health, Agriculture and Environment Ministries agreed that the birds should be destroyed after medical examinations discovered the virus in their brains.

According to Irit Rappaport, who is responsible for health and sanitation at the kibbutz, 25 kibbutz members have been infected with the virus since mid-August - out of about 350 in all of Israel - and 2 have died. [Of the approximately 350 Israelis infected with the virus since the epidemic began this summer, 26 have died. - Mod.CP] "Kabri has never suffered from mosquitoes, but we have a large population of pigeons here, and this aroused suspicions," she said. "Tests of the pigeons confirmed this, and we decided to thin out [the pigeon population] to check the spread of the disease." Dr. Michal Dar, chief physician for the Health Ministry's northern district, also said there appears to be a clear connection between Kabri's large pigeon population and the high number of kibbutz residents infected with the virus. "The number of victims at Kabri over the last 2 months is slightly less than half the number of victims in the entire north," she said.

[Unclear here whether the pigeons are wild or captive--a practise which historically has been quite common in Israel. -- LCL]

[8]
Date: Sun, 22 Oct 2000 21:10:33 +0800 From: Dr Muruga Vadivale vale@pop.jaring.my)
Source: Washington Post, Sun 22 Oct 2000, byline: Michael E. Ruane [edited]

Possible Additional Reservoir Hosts For West Nile Virus: Early on, scientists here suspected that one or more unknown players were involved in the transmission cycle [of WNV in North America]. Crows, in which the virus has a 90 to 100 percent mortality rate, are not necessarily the best host because their deaths kill the virus and end the cycle. "The crows are sort of collateral damage," said Stephen C. Guptill of the U.S. Geological Survey who has been tracking the virus. "If you're the virus, you don't want to kill off your host. You're not going to perpetuate your cause if your reason for survival is always going to be killed off. "So who is the real culprit here?" he said. "Who is the real carrier of the virus? It's something other than crows. If it's not the crows, then who is it?"

The common house sparrow became one of the early suspects in part because of its huge numbers in urban environments, where the virus seemed to thrive, and because sparrows had played a role in West Nile outbreaks in Egypt in the 1950s and South Africa in the 1970s. Some sparrows have been killed by the virus, but most apparently have not. Scientists decided to investigate.

Last year, according to Nicholas Komar, vertebrate ecologist at the Arbovirus Disease Branch of the U.S. Centers for Disease Control and Prevention in Fort Collins, Colo., experts studied an array of birds in New York City to see which ones might be harboring the infection. Sparrows came out high on the list, Komar said last week. "Given their incredible abundance in both urban and rural areas, it made sense that they would be a good candidate for an important vertebrate reservoir host. "Anything can be a host," he said. "Being a host is not that important. But some hosts will develop high levels of virus in their bodies and be able to transmit the virus to mosquitoes that feed on them. These are reservoir hosts. "Migrating birds may be involved in transporting the virus but are unlikely to be involved in local amplification of the virus," Komar said. "You need a resident population in a certain location that will serve to amplify the virus."

He and several colleagues decided to compare what is called the reservoir "competence" of several bird hosts compared sparrows, pigeons and some other bird species common to the Northeast. The birds were exposed to the bites of virus-infected mosquitoes and their blood tested every 24 hours. Most of the birds survived and developed antibodies. Sparrows, though, developed the highest virus levels and maintained them for the longest time, the team found. In at least one case, a sparrow maintained an "infectious viremia" for 5 days, whereas the longest a pigeon maintained it was one day. "The viremia profiles in wild birds suggest that the house sparrow is an important candidate reservoir host for the virus, the team concluded. The problem is, sparrows don't migrate. "We think that [there is] a different culprit that we have yet to identify." But Robert McLean, director of the USGS National Wildlife Health Center, in Madison, Wisc., said there are probably several culprits working as a team. Some, like the sparrow, keep the virus cooking locally. Others, dramatically so this year, have done the short- or long-range transportation.

[None of 541 serum samples taken from sparrows in New Jersey State during the course of the West Nile virus epidemic tested positive in tests carried out at the CDC. - Pro-MED Mod.CP]

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