# Presentation: 024839

## Sentinel Bird Surveillance for West Nile virus

**Nicholas Komar, Sc.D.**
**CDC-Arbovirus Diseases Branch**
**Fort Collins, CO**

**Sentinel Bird Surveillance for West Nile virus**

**Notes:**
The purpose of my talk is to introduce the traditional types of bird-based surveillance for arboviruses, and present to you how they have been applied to WNV surveillance in the year 2000.

## West Nile Virus Transmission Cycle

**West Nile Virus Transmission Cycle**

**WNV**

**WNV**

- Mosquito vector

- Incidental infections

- Bird
- reservoir hosts

- Incidental  infections

**Notes:**
First lets review the theory behind sentinel bird surveillance programs.  Birds are the main vertebrate amplification hosts in the WNV transmission cycle.  Mammals such as horse and human beings are simply incidental hosts.  Therefore, there should be many more birds infected than mammals, and infection should occur in birds prior to infection in mammals.  Thus birds should make effective sentinels for WN virus activity.

Sentinel bird seroconversions indicate risk of transmission to birds, but not necessarily transmission to mammals.
If bridge vectors are involved, then sentinel bird seroconversions may not be sufficient to indicate risk of human (mammal) transmission.

## WNV Surveillance Modalities

**WNV Surveillance Modalities**

**Dead birds (especially crows)**
- Mosquitoes
- Live wild bird sentinels
- Live captive sentinels (e.g. chickens)
- Veterinary surveillance
- Human surveillance

**Notes:**
Traditionally, sentinel birds have been used to monitor arbovirus transmission for SLE, WEE and EEE.  Wild birds are sometimes sampled as a type of sentinel, particularly in the states of Tennessee, Indiana, Illinois, Louisiana, Texas, and some others.  Chickens have been used extensively in states such as Florida, California, North Carolina, Louisiana and a few others.  
In both wild bird and chicken surveillance, the detection of seroconversion (from antibody-negative status to antibody-positive status) signals a transmission event. In this talk, I will present the yr-2000 experience with both these sentinel bird strategies for WNV surveillance. Later in the discussion, we will review the benefits and liabilities of each system.

## The success of sentinel bird surveillance depends solely on the effort expended by surveillance workers.

## WNV Surveillance Totals, 2000Reported to CDC thru 1/25/01

| Dead birds | 4312 |  |
| --- | --- | --- |
| Mosquito pools |   480 |  |
| Horses
Other mammals |     63
    25* |  |
| Humans |     21 |  |
| Sentinel chickens
HY wild birds  |     13** 
      7 |  |

- * Confirmed & Probable cases; ** includes 7 from NYC

**Notes:**
Although sentinel bird surveillance should be an effective tool, the numbers of positive chickens and hatch-year wild birds found positive for WNV antibodies in 2000 were smaller than all other types of surveillance indicators.  Clearly, sentinel bird surveillance must be increased and/or improved if it is to be used effectively.

## 			     % Pos for Neut Ab
      Species		NE Queens ’99	      S.I.’00        Chicken		  	63			  6
Pigeon		  	27			54
Mallard		    	  6			  8
House sparrow	  	60			  9
Cardinal		  	 --			69
Catbird		  	 --			33
Dog			  	11			 --
Horse		  	    	  6			 --
Human		    	  2.6			  0.5

**	****	****	****     ****% Pos for Neut Ab**
_**      **__**Species**__**	**__**	**__**NE Queens ’99**__**	**__**      S.I.’00        **_**Chicken****	****	****  ****	****63****	****	****	****  6**
**Pigeon****	****	****  ****	****27****	****	****	****54**
**Mallard****	****	****    ****	****  6****	****	****	****  8**
**House sparrow****	****  ****	****60****	****	****	****  9**
**Cardinal****	****	****  ****	**** --****	****	****	****69**
**Catbird****	****	****  ****	**** --****	****	****	****33**
**Dog****	****	****	****  ****	****11****	****	****	**** --**
**Horse****	****	****  ****	****    ****	****  6****	****	****	**** --**
**Human****	****	****    ****	****  2.6****	****	****	****  0.5**

**Notes:**
This slide presents data that supports the concept that sentinel birds programs could be an effective tool for WNV surveillance programs.  In both 1999 and 2000, vertebrate serosurveys were conducted in the outbreak regions, NE Queens in 1999; Staten Island in 2000.  The cumulative seroprevalences in different bird species late in the season indicates the potential for sentinel bird surveillance to be an effective tool for monitoring WNV transmission.

Chickens, pigeons, and house sparrows showed promise as sentinel species from the 1999 data.  Note that the high seroprevalence in Queens for these species was significantly greater than that for mammals, indicating that infections in birds were more frequent and easier to detect than infection in mammals.

In 2000, the same trend continues, with high prevalence of infection observed in pigeons, cardinals and catbirds.  Interestingly, chickens and house sparrows, two species commonly used as sentinels in arbovirus surveillance programs, did not score as high as expected.

## Can Chickens be used as Sentinels?

- Highly susceptible (for development of antibodies)
- Resistant to mortality
- Non-infectious to eachother
- Non-infectious to handlers
- Non-infectious to mosquitoes

**Notes:**
Should chicken be used as WNV sentinels?  Chickens are well established as useful sentinels for other arboviruses, but what about WNV?  An effective sentinel animal for WNV must satisfy the following criteria:

It must be highly susceptible to infection, so that all infected animals develop detectable antibodies.

It must be resistant to severe infection, or else there will be problems with animal welfare groups and animal use committees.  CDC does not permit any research done on animals where mortality is a desired endpoint; sensitive animals would have to be monitored closely and euthanized after showing signs of illness.

It should not spread the infection to other animals within the sentinel flock, because then infection would not accurately reflect natural transmission.

It should not present a threat to handlers when infected.

It should not present a threat to the community at-large by developing infectious-level viremia that could pass the virus back to mosquitoes in the community.

Although not all answers to these questions are currently available, chickens score fairly well on these tests.

## Pathogenicity of WNV in Chickens

**USDA-APHIS-NVSL:**
**Senne, Pederson, Hutto, Taylor, Schmitt, Panigrahy**
***Avian Dis 44:642-649, 2000***

**Notes:**
A published study found that 12 7-week-old chickens inoculated parenterally did not develop clinical illness, did not infect eachother, developed antibodies rapidly, and developed fairly low-level viremia.  However, cloacal shedding was observed, so handlers should wear gloves and other barrier protective devices.

## Do chickens develop WN viremia? 

**Do chickens develop WN viremia? **

**Notes:**
An as-yet-unpublished study at CDC evaluated infections in chickens by the natural route of mosquito-borne infection.  The findings of the USDA study were confirmed.  Chickens are essentially incompetent reservoir hosts for WNV.  The mean viremia measured in 13 adult birds was log 3.4, probably too low to infect most mosquitoes.  Interestingly, pigeons (a.k.a. rock doves) are similarly incompetent, whereas most passerine birds are competent.  In fact, this study in combination with the avian serosurvey data points to house sparrows as being important reservoir hosts, at least in urban areas such as northeastern Queens.

## Features of a Sentinel Chicken Program

**Chicken flocks established at known transmission foci**
**Birds are bled periodically**
**Serum samples sent immediately for testing**
**HI or M-ELISA test used for screen**
**N test for confirmation (3 days)**
**Positives replaced for accurate monitoring**

**Notes:**
Now that we have established that chickens should be good sentinels, I will now describe how they are used as sentinels.  Chicken flocks are placed in locations suspected to be transmission foci.  The flock characteristics should be standardized within a surveillance region so that regional comparison of transmission activity is possible.

Flocks are bled weekly or biweekly, screened by antibodies by IgM-capture ELISA or HI, and confirmed by neutralization (a more specific test).  Final results can be obtained within 1-2 weeks.

For detection of arbovirus activity, seropositive birds need not be replaced.  For monitoring force of transmission, positive birds are replaced by negative birds.

## New York City’s Sentinel Chicken Program

**Details provided by Dr. Bryan Cherry **
**13 coops (7 birds each) at live poultry markets in 4 boroughs, plus one flock of 15 in Staten Island**
**7 of 106 seroconverted (tested at Cornell)**
**One dead chicken tested WNV+ by NYSDOH**

**Notes:**
Details of NYC’s sentinel chicken program were provided by Dr. Bryan Cherry.  Most of NYC’s coops were placed outdoors at live poultry markets in all the boroughs except Staten Island, where chickens were kept in a pen at a State Park.  A total of 8 infections were documented out of about 100 birds in the program.

## Slide 12

**Notes:**
This photograph shows a coop used for WNV surveillance in New York City this past summer.  This coop holds 6 chickens.  Feces falls through the mesh floor.  Mosquitoes have access from below and from the sides.  

## New York State’s Sentinel Chicken Program

**Details from Dr. Millie Eidson, Dr. Greg Ebel **
**Flocks placed in 4 counties: Suffolk (103 birds), Rockland (24), Westchester (70), Onondaga (47)  **
**Sera screened by G-ELISA, confirmed by PRNT**
**1 of 244 seroconverted 4 Aug in Westchester**

**Notes:**
Details of NYS’s sentinel chicken program were provided by Drs. Millie Eidson and Greg Ebel.  Selected counties placed chicken flocks, typically with 6 birds per flock.  Placement was typically in outdoor areas such as parks.  Specimens were tested promptly at the Wadsworth Lab in Albany.  Only 1 seroconversion was documented, from serum collected August 4 in Wesatchester Co.  

## New Jersey’s Sentinel Chicken Program

**Details provided by Cheryl Farello, Dr. Bob Eisner**
**All 21 counties maintained 1-2 flocks of 3 birds each (more flocks in Ocean, Monmouth)**
**4 of 102 seroconverted **
**Sera screened by HI, confirmed by PRNT at USDA-APHIS-VS-NVSL**
**Dates of seroconversions are 27-29 Sep from Sussex, Middlesex, Morris, Essex counties**

**Notes:**
New Jersey established at least one or two flocks in every county, with 3 birds per flock.  Ocean County had 3 flocks and Monmouth County had 5 flocks.  Of the 33 flocks, 4 had single seroconversions, all taking place in the last week of September.  Specimens were screened by hemagglutination inhibition at the Dept. of Agriculture lab and confirmed by neutralization at NVSL in Ames, IA.

## Features of a Sentinel Wild Bird Program

**Sampling sites established at known transmission foci**
**Wild birds are captured periodically and banded**
**Serum samples sent immediately for testing.  Virus isolation may be attempted.**
**HI, ELISA or PRNT used for screen**
**PRNT for confirmation (3 days)**
**Hatch-year birds most useful, or recaptured adults, of targeted species**

**Notes:**
Sentinel wild bird programs rely on capturing large numbers of wild birds at regular intervals in locations known for arbovirus transmission.  These birds are banded for future identification and blood-sampled from the jugular vein.  
	Blood samples are tested immediately for antibodies and in some cases, viruses as well.  Several methods are available to screen serum samples for antibodies.  Neutralization tests are the most sensitive and specific but are slow (3 days) and require BSL-3 for WNV.  HI is a quick, accessible alternative that is low in specificity, a bonus if you are looking for both WNV and SLE.  ELISA has been problematic for testing specimens from a variety of species.  Multi-species ELISAs have been developed.  
	Seroconversion events require sampling individual birds repeatedly (recapture rates are generally low).  Birds aged as < 1 yr old that test positive are treated as seroconversions. 
	Similar species should be sampled consistently to permit comparison of transmission activity over time and space.  Knowledge of frequently exposed species (e.g. from serosurveys) is useful for targeting particular species (e.g. pigeons for WNV).  Knowledge of important reservoir hosts is also useful for the same reason (e.g. house sparrows for WNV).

## Summary of Wild Bird Surveillance, NYC

_**Species**__**	**__**	**__**      n**__**	**__**	**__**No. POS**__**	**__**  %**_
**House Sparrow      440****	****     3****	****	****0.7%**
**Other ****	****	****     150****	****     1****	****	****0.7%****	**

**Line list:****Jul 21****	****House Sparrow Queens-Floral Park****Aug 2****	****Mockingbird****	****    Brooklyn-Sunset Park****Aug 9****	****House Sparrow  Bronx-Orchard Beach****Aug 21House Sparrow Queens-Forest Park**

**Notes:**
In New York City, sentinel wild bird surveillance did not occur at the same sites over time, so transmission was not monitored.  Rather, wild birds were used as an additional tool for detecting WNV activity in new locations in order to make spray decisions.  Nonetheless, house sparrows appeared to be an effective target species compared with other species tested.

## First WNV Surveillance Events, 2000

- Aug

- Sep

- Oct

- Jul

- Jun

- Apr

- Mar

- Viral activity (inferred)

**Crow,**
**Suffolk**

***Oc. japonicus*****,**
** ****Westchester;**
***Cx. pipiens*****,**
** ****Richmond**

**Horse,**
**Richmond**

**Human,**
**Richmond**

**Sentinel **
**Chicken,**
**Westchester**

**Crow,**
**Richmond**

**Sentinel wild bird, Suffolk**

**Notes:**
I don’t have time to summarize the pros and cons of each type of sentinel bird surveillance system, but I will point out that sentinel wild birds and chickens were preceded by dead birds and positive mosquito pools.  Further discussion of the pros and cons of sentinel bird surveillance is welcome later in this session.  

## Time’s Up!

**Notes:**
Thank you.

## Does a dead bird represent local WNV transmission?

## Culex sp. WN virus infectionsJuly 15-24, 2000

| Site with recentdead crow/jay | # Cx. pipiens/restuans tested | # WNV + Pools | MIR* 
(95% Conf. Int.) |
| --- | --- | --- | --- |
| Babylon
(Suffolk Co) | 4,728 | 30 | 6.3 |
| Floral Park (Queens Co) | 6,342 | 2 | 0.3 |
| New Rochelle (Westchester Co) | 6,150 | 4 | 0.6 |

*** ****Minimum Infection Ratio = # infected/1000 tested**

## House Sparrow SeropositivesJuly 15-24, 2000

| Site | # Hatch year house sparrows tested | #  WN seropositive | % WN seropositive  |
| --- | --- | --- | --- |
| Babylon
(Suffolk Co) | 76 | 1 | 1.3% |
| Floral Park (Queens Co) | 87 | 1 | 1.1% |
| New Rochelle (Westchester Co) | 86 | 0 | 0 % |