Attachment 3

WEST NILE VIRUS- BACKGROUND INFORMATION AND PUBLIC EDUCATION PLAN FOR CAPITAL HEALTH

April 21, 2003 – DRAFT ONLY

EXECUTIVE SUMMARY

Surveillance, public education, elimination of breeding sites and insecticide applications to control the aquatic stages of mosquitoes will be the strategies used toreduce the risk of West Nile virus (WNV) transmission to humans. Actions can be divided into three components: WNV surveillance, human disease surveillance and control programs.

WNV Surveillance Program

The aim of the surveillance program is to provide public health officials with a picture of the status of WNV in the community, the concentration of potential vectors and the possibility of disease development. While the program may not prevent an outbreak of WNV in this health region, it may be useful in developing a disease control strategy for subsequent years. The surveillance program shall be composed of two parts:

1)Dead bird surveillance: The presence of WNV in dead birds is usually the first indicator of the presence WNV-infected mosquitoes in an area. One model for “predicting” a WNV outbreak in human population uses 1.5 WNV-positive dead crow per square mile as the threshold number for forecasting the likelihood of an outbreak in humans. The presence of infected dead birds within the City of Edmonton will also be a trigger to increase mosquito surveillance in an area.

2)Mosquito surveillance: The aim is to continue monitoring standing water bodies for the development of mosquito larvae as is the current strategy in the City of Edmonton’s nuisance control program. The purpose is to identify areas likely to serve as breeding grounds for Culex and other mosquito vectors of WNV. In addition, the City of Edmonton Community Service Department will continue to use New Jersey Light traps to monitor for an increase in adult mosquitoes. Once WNV has been confirmed within the control program area, through dead bird surveillance, the City Community Services Department will use CO2 baited CDC traps to facilitate testing for the presence of WNV in different mosquito species.

Human Disease Surveillance Program

Identify the presence of virus in humans and animals. Human surveillance involves the reporting of suspected cases by physicians and laboratories to the regional MOHs and on to Alberta Health & Wellness and Health Canada.

Human Disease Control Program

The aim of the disease control program is to minimize human exposure to potentially infected mosquitoes. This can be achieved by reducing the mosquito population through source reduction and targeted treatments to disrupt the build-up of WNV in wild bird populations caused by mosquito species that specialize on birds for blood meals, (avian-mosquito amplification cycle), and by general personal protection activities.

1. Mosquito control: The City of Edmonton Community Services Department will use a selection of different larvicides and source reduction techniques to reduce known mosquito populations. This would be the most environmentally acceptable and effective means of reducing numbers of those adult mosquitoes that are most capable of infecting people with the virus.

2. Public education (protection from mosquitoes): The aim is to make people aware of the need to protect themselves from mosquito bites and avoiding contact with mosquitoes. The practice of protection against mosquito bites (mosquito hygiene) includes:

  • Source and habitat reduction- eliminate sources of standing/stagnant water where mosquitoes can complete their life cycle around the home, and
  • Avoidance of biting mosquito and personal protection- minimize human exposure through the use of repellent, other activities and precautions.

The success of implementing these strategies this year can be used to assess the need for other strategies, such as a broader based long-term community-level approach to mosquito surveillance and control programs.

WEST NILE VIRUS: BACKGROUND DOCUMENT
I. HISTORY

West Nile Virus (WNV) was first isolated from a febrile adult woman in the West Nile District of Uganda in 1937. The virus became recognized as the cause of severe human meningoencephalitis in elderly patients during an outbreak in Israel in 1957. WNV is endemic in part of Africa, southern Europe, the Middle East, west and central Asia, Oceania (sub-type Kunjin). Recent outbreaks of WNV encephalitis in humans were recorded in Algeria in 1994, Romania in 1996-1997, the Czech Republic in 1997, the Democratic Republic of the Congo in 1998, Russia in 1999, the United States in 1999-2000, and Camargue, France and Israel in 2000. It is not known where the U.S. virus originated, but it is most closely related genetically to a 1998 isolate from a goose in Israel.

WNV is classified as an arbovirus (viruses that are transmitted by blood feeding insects). The virus belong to the flavivirus family (Flaviviradae) which includes the viruses that cause Japanese encephalitis, St. Louis encephalitis, Bovine Virus Diarrhea, Pestivirus diseases such as Hog Cholera and Border Disease, Hepatitis C, Dengue Fever and Yellow Fever.

The previous largest human epidemic occurred in Cape Province, South Africa in 1974 when approximately 3,000 clinical cases of the virus were recorded. WNV is one of the most widespread flaviviruses, even before its recent entry into North America. During the 1950s, an estimated 40% of the human population in Egypt’s Nile Delta was seropositive for the virus.

II. THE SPREAD OF WNV IN NORTH AMERICA

1) US

1999

WNV was first isolated in New York City in 1999 from a dead American Crow on September 14, 1999 by the National Veterinary Services Laboratory. It was later confirmed as the cause of a human encephalities case that occurred in August 1999. WNV cases centered in Queens, NYC, and were also detected in other locations within a 75-mile radius (NY, NJ and Connecticut). The only case outside the NYC metropolitan area was a single crow in Maryland. A total of 62 people were hospitalized with infection of CNS, of whom 7 (11%) died.

2000

WNV spreaded to 12 US states and Washington DC. Despite a much larger range, there was less human illness reported, with 20 hospitalizations with CNS infection and 2 individuals died (10%).

2001

WNV continued to spread to 27 US states and Washington DC, affecting at least 64 people in 10 states, resulting in 10 deaths (14%). At least 12 of the severe cases were persons in their thirties to fifties. There was one case involving a 19-year old. WNV was found in at least 80 bird species (including most Corvids) and 8 mammal species.

2002

The 2002 WNV epidemic in the US was the largest arboviral menigoencephalitits epidemic documented in the Western Hemisphere, and the largest West Nile Menigoencephalitis (WNME) epidemic. It was most intense in the central US Great Lakes region. There was one human case in LA county and a WNV-infected horse in Washington state indicated the complete transcontinental movement within 3 years.

In total, WNV was found in mosquitoes, birds and horses in 44 states and Washington DC. 3,389 human cases were recorded in 37 states and DC. 69% of human cases developed WNME, 21% West Nile Fever (WNF) and 10% had unspecified illness. Five states: Illinois (774 cases), Michigan (475), Ohio (409), Louisiana (319) and Indiana (202) accounted for 64% of all reported cases.

Illnesses occur from June 10 to Nov 4 in Southern states, and July 10 to Oct 28 in Northern states. WNME peaked during the week ending Aug 17 and Aug 24 for the southern and northern states, respectively. For human cases, the age ranged from 1-99. Of the 2,354 persons with WNME, 199 (9%) died, two (0.3%) of 704 persons with WNF died. Both fatal cases with WNF were over the age of 80. The median age of 2001 decedents was 78 (range 24-99). Although older persons are at higher risk for WNME and death, persons of any age might develop severe neurologic disease.

There were also five person-to-person cases (organ transplantation, blood and blood product transfusion and breast feeding) and intrauterine infection. A lab case involved percutaneous inoculation, and the handling of fluids or tissue known or suspected to be WNV-infected. An intrauterine case was recorded from transplacental WNV transmission. Pregnant women should take precautions to reduce their risk for WNV infection

2) Canada

In 2002, WNV was found in birds and mosquitoes from five provinces (Manitoba, Nova Scotia, Ontario, Quebec and Saskatchewan), with American Crows, Blue Jays, Common Ravens and Black-Billed Magpies as the major bird species affected. There was a total of 116 probable positive human cases, and 272 confirmed human cases. Eleven people died from WNME. In Alberta, first human case in Oct 2002, it was likely that this individual became infected while traveling in Louisiana and Texas over the summer months. A second human case announced in December in Edmonton, was also travel related, having visited Ontario two weeks prior to the onset of symptoms.

Canadian Blood Services hopes to have plans and tests ready to screen out blood donations containing active WNV, and are developing contingency plans if those tests are not available in the summer of 2003.

III. CAPITAL HEALTH 2003 WNV RESPONSE PLAN

Surveillance, public education, elimination of breeding sites and insecticide applications to control aquatic stages of mosquitoes will be the strategies used toreduce the risk of West Nile virus (WNV) transmission to humans. Actions can be divided into three components: WNV surveillance, Human disease surveillance and control programs.

WNV Surveillance Program

The aim of the surveillance program is to provide public health officials with a picture of the status of WNV in the community, the concentration of potential vectors and the possibility of disease development. While the program may not prevent an outbreak of WNV in this health region, it may be useful in developing a disease control strategy for subsequent years. The surveillance program shall be composed of three parts:

1) Dead birds surveillance:

The Corvidae family accounts for 90% of WNV-infected birds, with crows having the highest rate of infection. WNV is particularly lethal for the American Crow and blue jays, and can also infect magpies, ravens and other types of jays. Wild birds are the primary vertebrate vector of WNV and act as an amplifying host. Their high viremia serves as a reservoir for the virus. WNV is less likely to kill other birds such as robins, sparrows, pigeons, which carry the virus in their blood, but they can re-infect mosquitoes that bite them, which can then spread it to mammals including people and horses.

The presence of WNV in dead birds is usually the first indicator of the presence of WNV-infected mosquitoes in an area (62% of human cases are preceded by the presence of the virus in dead birds). One model for “predicting” a WNV outbreak in human population uses 1.5 WNV-positive dead crows per square mile as the threshold number for forecasting the likelihood of an outbreak in humans. The presence of an infected dead bird within the City of Edmonton will also be a trigger to increase mosquito surveillance in an area. One US study found bird-to-bird transmission could occur in a laboratory setting.

If crows, magpies, ravens and jays are found within 48 hours of the time of death, and if the dead bird can be kept cool or frozen, it can be submitted to Alberta Fish and Wildlife for testing. Within the City of Edmonton, representatives from the City Pound (496-8860) will pick up dead birds and deliver them to Alberta Fish and Wildlife Division of Alberta Sustainable Resource Development (ASRD). Outside the City of Edmonton, the public can contact Fish and Wildlife offices (Edmonton: 427-3574; Stony Plain: 963-6131). The general public can use gloves or a shovel to pick up the dead bird and place it in a plastic bag. Place the bird inside one additional plastic bag, tightly closed and refrigerate. If it cannot be delivered to a laboratory for testing within 36 hours, the bagged dead birds should be frozen and delivered in a frozen state (without thawing). Sparrows, starlings, pigeons, finches, robins and blackbirds are not currently tested. There is no evidence at this point that a person can be infected from handling infected birds

2) Mammal surveillance:

Most non-human cases occurred in horses (99.9%), but WNV has also been found in 230 other species, including black bear, squirrels, chipmunks, raccoons, skunks, rabbits, cats, sheep, cattle, pigs, monkeys, reindeer and alligators. 8-11% of dogs had antibody titers to WNV, but they do not become ill. In 2001, 33% of infected horses died or were euthanatized. Horses develop viremias of low magnitude and short duration so infected horses are unlikely to serve as important amplifying hosts for the WNV in nature. A vaccine is available for horses through veterinarians (for a price).

3) Mosquito surveillance:

Since 1999, 36 WNV-infected mosquito species have been identified. Culex (pipiens, restuans, salinarius, quinquefasciatus and tarsalis) accounted for 55% of WNV-positive pools. Culex breeds in standing water, especially in water polluted with organic matter. Though they prefer to bite birds, if breeding sites are available near people’s homes and domestic animals, Cx tarsalis may bite people and domestic animals. Culex mosquitoes are most active at dawn and dusk.

Mosquitoes become infected when they feed on infected birds, which may circulate the virus in their blood for a few days. Infected mosquitoes can then transmit WNV to humans and animals while taking a blood meal. The virus is passed to the host from infected salivary glands which supply anticoagulent saliva into the host during the blood-feeding process. It should be noted that most mosquitoes are not infected with WNV, and most mosquito bites will not lead to a WNV infection.

It is not known if other blood sucking insects and ticks play a role in disease transmission.

The aim of the mosquito surveillance program is to continue monitoring standing water bodies for the development of mosquito larvae as is the current strategy in the City of Edmonton’s nuisance control program. The purpose is to identify areas likely to serve as breeding grounds for Culex and other mosquito vectors of WNV. In addition, the City of Edmonton Community Services Department will continue to use New Jersey Light traps to monitor for increases in adult mosquito populations and determine the presence and incidence of mosquito species believed to be WNV vectors. Once WNV has been confirmed within the control program area, the City Community Services Department will also use light CO2 baited-CDC traps to catch live mosquitoes to test for the presence of WNV in different mosquito species. In the City of Edmonton, Culex tarsalis may be the major vector for WNV. During normal years, the Cx. tarsalis population is very small when compared to numbers of other mosquito species in the Edmonton area.

Human Disease Surveillance:

Disease surveillance includes the identification of virus in humans and animals. Human surveillance involves the reporting of suspected cases by physicians and laboratories to regional MOHs and on to Alberta Health & Wellness and Health Canada.

Most WNV infections in people do not cause any illness. Those with mild WNV encephalitis can run a fever and have head and body aches. They can also develop skin rashes, experience extreme tiredness and have swollen lymph nodes. Individuals with more serious infections can develop a stiff neck, stupor, become disoriented, develop tremors, high fever, become paralyzed, convulse and go into a coma. The incubation period ranges from 5 to 15 days.

About 30% of those infected in 1999 reported minor ‘flu-like’ symptoms, and 20% of individuals infected with WNV will develop clinical signs of illness or experience West Nile Fever. Fewer than 1% (1-in-150) became seriously ill, with CNS infection (encephalitis and/or meningitis)

Older people and those that are immuno-compromised are at greater risk of developing severe disease complications. Children are not in a higher risk group. At the present time, there is no human vaccine or medication specific to treat WNV symptoms.

Testing for WNV is a complex process that takes a long time. While the results are important to scientists and medical doctors studying the disease, they would not be very useful to an individual. There is no particular cure for WNV, so a sick person does not become better off by being tested for WNV infection.

Human Disease Control Program

The aim of a vector and disease control program is to reduce mosquito population through source reduction, disrupt the avian-mosquito amplification cycle, and thereby minimize human exposure. This can all be achieved through the following activities:

1) Mosquito control:

The City of Edmonton Community Services Department will use a selection of different larvicides and source reduction techniques to reduce nuisance mosquito and some vector populations. This would be the most environmentally acceptable and effective means of reducing numbers of those adult mosquitoes that are most capable of infecting people with the virus. It should be noted, however, that the City of Edmonton mosquito control program only extends a few kilometers into neighbouring counties. Helicopter and ditch spraying will target mainly nuisance mosquitoes that may not be major vectors for WNV.