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RECOMMENDATIONS
FOR
WEST NILE VIRUS SURVEILLANCE IN THE CARIBBEAN
December,
2004
Introduction
In late summer 1999 an outbreak of West Nile (WN) encephalitis was documented for the first time in New York and since then West Nile virus (WNV) has been spreading in the United States (US), Canada, Central America and the Caribbean basin. Today WNV infection is recognized as the largest arboviral meningoencephalitis epidemic ever recorded in the US and Canada.
The first human WN encephalitis case in the Caribbean was reported at the end of 2001 in Cayman Islands. Subsequently, in January 2002, WNV activity was observed in migratory and resident birds in Jamaica, Dominican Republic and Puerto Rico. These reports marked the earliest evidence of WNV introduction into the Caribbean. WNV activity has also been documented from a serosurvey in which 360 serum samples were collected in healthy horses in Guadeloupe between June 2002 and January 2003. The overall prevalence of IgG antibodies to WNV increased from 2.8 % in June 2002 to 50% in January 2003, which represents a clear seroconversion in horses within a 6 month period. In October 2003, WNV was identified in horses in Belize. The second human WN encephalitis case was reported in the Bahamas July 2003. The most recent identification of WNV in the Caribbean was in Trinidad, where in serosurvey of 60 horses and 40 birds conducted in October, 2004, WNV antibodies were identified in 2 horses (3%) and 2 birds (5%).
WNV is a member of the Flaviviriae family (genus Flavivirus). Serologically, it is a member of the Japanese Encephalitis serocomplex, which also includes St. Louis, Japanese, Kunjin, and Murray Valley Encephalitis viruses. Human and equine outbreaks of WN have been recorded in Africa, Southern Europe, Asia and North America and Canada.
WNV is typically transmitted between birds and mosquitoes. Mammals can become infected if bitten by an infected mosquito, especially the Culex species, but individuals in most species of mammals do not become ill from the virus infection. Mammals are considered to be "dead-end hosts" because the virus does not generally multiply in their blood to levels high enough to be infective. Thus mosquitoes that bite an infected person or horse cannot pick up the virus from them and spread it further. Four novel routes of WNV transmission from humans to humans are well documented: blood transfusion, organ transplantation, transplacental and breast-feeding.
West Nile Virus (WNV) Infection in humans
Clinical Features
Mild Infection
Most WNV infections are mild and often clinically unapparent.
Approximately 1 in 5 (20%) of infections develop into mild illness (West Nile fever).
The incubation period is thought to range from 3 to 14 days.
Symptoms generally last 3 to 6 days.
The mild form of WNV infection presents as a febrile illness of sudden onset often accompanied by malaise, anorexia, nausea, vomiting, eye pain, headache, myalgia, rash and lymphadenopathy.
Severe Infection
Approximately 1 in 150 (0.7%) infections will result in severe neurological disease.
The most significant risk factor for developing severe neurological disease is advanced age.
Encephalitis is more commonly reported than meningitis.
Symptoms occurring among patients with severe disease include fever, weakness, gastrointestinal symptoms and a change in mental status.
A minority of patients with severe disease develop a maculopapular or morbilliform rash involving the neck, trunk, arms, or legs.
Patients may experience severe muscle weakness and flaccid paralysis.
Neurological presentations include
ataxia and extrapyramidal signs
cranial nerve myelitis abnormalities
optic neuritis
polyradiculitis
seizures
Although not observed in recent outbreaks, myocarditis, pancreatitis, and fulminant hepatitis have been described.
Clinical Suspicion
Diagnosis of WNV infection is based on a high index of clinical suspicion and obtaining specific laboratory tests.
WNV (and other arboviral diseases such as St. Louis encephalitis) should be strongly considered in adults >50 years who develop unexplained encephalitis or meningitis.
The local presence of WNV enzootic activity or other human cases should further raise suspicion.
Obtaining a recent travel history is also important.
WNV should be considered in all persons with unexplained encephalitis and meningitis.
West Nile Virus Infection in Horses
Horses may become infected with or without showing any clinical signs. Clinical symptoms which may be present include:
• Fever (not a common sign)
• Ataxia or stumbling and
lack of coordination
• Depression or apprehension to stand
•
Weakness of limbs, partial paralysis, or the inability, muscle
twitching
• Death
West Nile Virus Infection in Birds
In some bird species WNV causes disease (often fatal) in a large percentage of infected birds, particularly in Corvids (crows, blue jays, ravens). Many other bird species can carry the virus and develop immunity without becoming sick (e.g. chickens). In some infected birds viremia lasts 1-4 days. Sick birds may show the following manifestations:
Hemorrhagic manifestations, such as blood in urine and feces
Myocardial degeneration or pancreatitis.
Neurological symptoms such as anorexia and weight loss paralysis, depression, weakness, tremors, disorientation and encephalitis (possibly leading to death).
West Nile Virus Infection in Other animals:
WNV infection has been reported in a variety of animal species. WNV has been reported to cause serious or fatal illness in mammal species, including reindeer, squirrels, wolves and dogs. In some serosurveys, black bears and deer were also found to be seropositive with neutralizing antibodies. Implications of these findings, in terms of WNV transmission and disease ecology are unclear, since the bears and deer were not apparently sickened by the virus and it is believed that mammals are dead end hosts, not able to transmit the disease. WNV is highly pathogenic to alligators and has been implicated in two epizootics among captive animals
Recommended WNV Surveillance Activities in the Caribbean
The aim of surveillance activities is to detect WN virus activity in host and vector populations in order to take appropriate measures in terms of prevention and control of infection. The Caribbean Epidemiology Centre (CAREC) recommends the use of the following guidelines for WNV surveillance in the Caribbean.
Human WNV Surveillance.
The objective of human surveillance is to detect severe cases of WN virus infection.
Active: An epidemiological investigation of all cases of viral neurological diseases within the last 2-3 years should be undertaken.
Passive:
Hospital services should notify their local health authorities of all suspected cases of WN infection.
Public and private clinics should be alerted for collaboration in reporting of WN cases and in the collection blood samples for laboratory testing.
There should be an increase in surveillance for neurological syndromes and dengue-like illnesses. Appropriate specimens should be collected and laboratory investigations conducted. Blood samples must be taken indicating date of onset of illness and date that the sample was taken and sent to CAREC for identification.
Case Definitions
A suspected case is any person admitted to hospital presenting with fever and severe neurological manifestations (varying from aseptic meningitis to encephalitis) of unknown aetiology.
A confirmed case is a suspected case with one of the following criteria:
Isolation of WN virus or detection of WN viral antigen or viral genome in serum or CSF;
A greater than fourfold serial change in plaque reduction neutralizing (PRNT) antibody titer to WN virus in paired serum or CSF samples.
Specimens
Cerebral spinal fluid (CSF) and paired acute-phase (collected 0-8 days after onset of symptoms) and convalescent (collected 8-21 days after the acute specimen) serum samples are to be submitted to CAREC to ensure the etiological diagnosis. At least 0.5 ml of serum and 1.0 ml of CSF is required for serology testing.
If an autopsy is performed, brain tissue should be collected as both fresh-frozen and formalin-fixed specimens.
Label each specimen container with patient name or ID, patient date of birth, type of specimen and date of collection.
Complete the accompanying laboratory request form supplying all clinical and epidemiological information available.
Standard biosafety procedures should be implemented for handling any specimen in clinical and microbiological laboratories.
Universal precautions for necropsy must be used such as: personal protection (protective clothing, gloves, face shields or eye protection), disposal of contaminated carcasses or specimens and disinfection of all items after specimen processing.
All collection, processing, preservation and shipping of specimens must be according to the WHO Biosafety Guidelines.
http://www.who.int/emc-documents/biosafety/whoemc973c.html http://www.iata.org/dangerousgoods/index and http://www.hazmat.dot.gov/rules.htm
Diagnostic Testing
The most efficient diagnostic method is detection of IgM antibody to WNV in serum collected within 8-21 days of illness onset or cerebral spinal fluid (CSF) collected within 8 days of onset of illness using the IgM antibody capture enzyme-linked immunosorbent assay (MAC-ELISA).
Since IgM antibody does not cross the blood-brain barrier, IgM antibody in CSF strongly suggests central nervous system infection.
Patients who have been recently vaccinated against or recently infected with related flaviviruses (e.g., yellow fever, Japanese encephalitis, dengue) may have positive WNV MAC-ELISA results.
NB: Detection of WN virus-specific IgM and/or IgG (by EIA) antibody in a single serum or CSF specimen must be confirmed by any of the above techniques.
Veterinary Surveillance
2.1 Horses
Active: Conduct sero-surveillance in local horse populations prior to vaccination* against West Nile Virus.
Passive
Instruct horse owners to contact local veterinarians at the first sign of neurological manifestations in their horses.
Instruct local veterinarians to report cases of horses with neurological symptoms and to collect serum samples and refer them to appropriate authorities for testing.
*Note: Horse owners should be advised to vaccinate their animals
Specimens
Veterinary practitioners must notify cases of horses with neurological manifestations and collect pairs of serum samples and CSF if possible as recommended for human surveillance.
Birds
The experience in the United States and Canada with WNV has indicated that virus activity can be first detected by morbidity and mortality in wild bird populations followed by sentinel chicken and mosquito populations. However bird mortality it is not an ideal indicator in Central America and the Caribbean because the members of the Corvidae family susceptible to WNV are less common in tropical areas.
The following surveillance activities should be undertaken through close collaboration by the Ministries of Health, Environment and Agriculture.
Active: Periodic sero-surveillance of local sentinel chicken populations focusing in areas where native bird species are abundant.
Passive:
Establish a system for reporting dead birds. E.g. a hotline telephone reporting system.
Instruct the public how to collect dead birds and transport them to key personnel designated by the Ministries of Health, Environment and Agriculture i.e. Veterinarians, Ministry of Agriculture, Health Centers etc.
Collaborate with bird watching organizations, nature clubs, zoos etc. to collect and report dead birds to the appropriate authorities.
Specimens
If any bird mortality is observed in a country, veterinary practitioners, sanitary and wild life agencies are requested to collect fresh carcasses (<48 hrs old) or moribund wild birds for submission for viral diagnosis.
Bird carcasses or their tissues should be collected according to standard biosafety precautions for veterinary necropsy. Collect bird carcasses wearing gloves or protect your hands with the collecting plastic bags. Place each carcass in individual plastic bags.
Label the bag with the animal species, locality collected, and date of collection. Send immediately to the veterinary laboratory.
If necropsy is performed, collect brain, spleen and heart tissues in individual containers. Use personal protection wearing protective clothes, gloves, face shields or goggles during the animal necropsy.
Label each specimens container with animal species, type of specimen, date of collection.
Guarantee the sanitary disposal of contaminated carcasses or specimens.
Disinfect all items after specimen processing. Commercially available household bleach solution containing 5.25% hypochlorite diluted 1:10 is effective in routine decontamination of surfaces and instruments.
Entomological Surveillance.
In the Northern US and Canada, WNV has been isolated from 43 species of mosquitoes. The majority of isolates came from Culex (Culex)spp. Laboratory studies indicate that most Culex(Culex) spp. were competent, though only moderately efficient, laboratory vectors of WNV. Ae. albopictus, Oc. japonicus, and Cx. tarsalis were the most efficient laboratory vectors tested. With very few exceptions, the transmission rate for individuals with a disseminated infection was high (>75%). Cx pipiens, Cx quinquefasciatus, Cx salinarius, and Cx nigripalpus are potential local vectors in the Caribbean however other local species that feed both on birds and mammals may also play an important role in transmission.
Active surveillance: Collection of adult mosquitoes using CDC light traps or Reiter Gravid Ovitraps in areas where suspected human or animal cases of WNV have occurred. Determine species of mosquitoes that are active near urban human populations and map their sources (breeding sites) for control or elimination. Mosquitoes may be collected, sorted by species and persevered for viral isolation in order to incriminate the mosquito species responsible for transmission.
Biosafety: Universal precautions for animal necropsy must be used such as: personal protection (protective clothing, gloves, face shields or eye protection); disposal of contaminated carcasses or specimens; and disinfection of all items after specimen processing.
All collection, processing, preservation and shipping of specimens must be according to the WHO Biosafety Guidelines.
http://www.who.int/emc-documents/biosafety/whoemc973c.html http://www.iata.org/dangerousgoods/index and http://www.hazmat.dot.gov/rules.htm
For complete packaging instructions see IATA guidelines:
http://www.iata.org/dangerousgoods/index
IMPORTANT: Before sending samples, please contact CAREC Customer Service (Telephone: 868-622-4261 extensions 221, 248,251)
For questions concerning Epidemiological Surveillance, please contact Epidemiology Division, telephone 868-622-2152, CAREC-EPIDEMIOLOGY@carec.paho.org; Dr. Christian Frederickson, Entomologist, telephone 868-622-2324, frederch@carec.paho.org or Dr. Rosa Alba Salas, Virologist, telephone 868-622-2324, salasros@carec.paho.org
