West Nile Virus
West Nile Virus is a flavivirus commonly found in Africa, West Asia, and the Middle East and was first discovered in the U.S. in 1999. It is closely related to St. Louis encephalitis virus found in the United States. The virus can infect humans, birds, mosquitoes, horses, and some other mammals.
It is a cause of mild disease in people, characterized by flu-like symptoms. West Nile fever typically lasts only a few days and does not appear to cause any long-term health effects. West Nile Virus is transmitted through the bite of an infected mosquito.
More severe disease due to a person being infected with this virus can be West Nile encephalitis, West Nile meningitis or West Nile meningoencephalitis. Encephalitis refers to an inflammation of the brain, meningitis is an inflammation of the membrane around the brain and the spinal cord, and meningoencephalitis refers to inflammation of the brain and the membrane surrounding it.
West Nile virus has been commonly found in humans and birds and other vertebrates in Africa, Eastern Europe, West Asia, and the Middle East, but until 1999 had not previously been documented in the Western Hemisphere. The origin of the U.S. virus is unknown, but it is most closely related genetically to strains found in the Middle East
ADDITIONAL INFORMATION ON WEST NILE VIRUS
US Centers for Disease Control and Prevention’s West Nile Virus Section
OREGON’S WEST NILE VIRUS HOTLINE
Oregon West Nile Virus
Information Line
Toll-free 866-703-4636
(866-703-INFO)
St. Louis Encephalitis
In the United States, the leading cause of epidemic flaviviral encephalitis is St. Louis encephalitis (SLE) virus.
SLE is the most common mosquito-transmitted human pathogen in the U.S. While periodic SLE epidemics have occurred only in the Midwest and southeast, SLE virus is distributed throughout the lower 48 states.
Since 1964, there have been 4,437 confirmed cases of SLE with an average of 193 cases per year (range 4-1,967). However, less than 1% of SLE viral infections are clinically apparent and the vast majority of infections remain undiagnosed.
Illness ranges in severity from a simple febrile headache to meningoencephalitis, with an overall case-fatality ratio of 5-15 %. The disease is generally milder in children than in adults, but in those children who do have disease, there is a high rate of encephalitis. The elderly are at highest risk for severe disease and death.
During the summer season, SLE virus is maintained in a mosquito-bird-mosquito cycle, with periodic amplification by peridomestic birds and Culex mosquitoes. In Florida, the principal vector is Cx. nigripalpus, in the Midwest, Cx. pipiens pipiens and Cx. p. quinquefasciatus and in the western United States, Cx. tarsalis and members of the Cx. pipiens complex.
Western Equine Encephalitis
The alphavirus western equine encephalitis (WEE) was first isolated in California in 1930 from the brain of a horse with encephalitis and remains an important cause of encephalitis in horses and humans in North America, mainly in western parts of the U.S. and Canada. In the western United States, the enzootic cycle of WEE involves passerine birds, in which the infection is inapparent, and culicine mosquitoes, principally Cx. tarsalis, a species that is associated with irrigated agriculture and stream drainages. The virus has also been isolated from a variety of mammal species. Other important mosquito vector species include Aedes melanimon in California, Ae. dorsalis in Utah and New Mexico and Ae. campestris in New Mexico. WEE virus was isolated from field collected larvae of Ae. dorsalis, providing evidence that vertical transmission may play an important role in the maintenance cycle of an alphavirus.
Expansion of irrigated agriculture in the North Platte River Valley during the past several decades has created habitats and conditions favorable for increases in populations of granivorous birds such as the house sparrow, Passer domesticus, and mosquitoes such as Cx. tarsalis, Aedes dorsalis and Aedes melanimon. All of these species may play a role in WEE virus transmission in irrigated areas. In addition to Cx. tarsalis, Ae. dorsalis and Ae. melanimon, WEE virus also has been isolated occasionally from some other mosquito species present in the area. Two confirmed and several suspect cases of WEE were reported from Wyoming in 1994. In 1995, two strains of WEE virus were isolated from Culex tarsalis and neutralizing antibody to WEE virus was demonstrated in sera from pheasants and house sparrows. During 1997, 35 strains of WEE virus were isolated from mosquitoes collected in Scotts Bluff County, Nebraska.
Human WEE cases are usually first seen in June or July. Most WEE infections are asymptomatic or present as mild, nonspecific illness. Patients with clinically apparent illness usually have a sudden onset with fever, headache, nausea, vomiting, anorexia and malaise, followed by altered mental status, weakness and signs of meningeal irritation. Children, especially those under 1 year old, are affected more severely than adults and may be left with permanent sequelae, which is seen in 5 to 30% of young patients. The mortality rate is about 3%.
Canine Heartworm
The first published description of heartworm in dogs appeared more than 100 years ago in an issue of “The Western Journal of Medicine and Surgery.” Heartworm in cats was first described in the early 1920s. Since then, naturally acquired heartworm infection in cats and dogs is identified as a worldwide clinical problem. Despite improved diagnostic methods, effective preventives and increasing awareness among veterinary professionals and pet owners, cases of heartworm infection continue to appear in pet dogs around the world. The diagnosis of the disease is still complex and elusive in cats.
What do we know about it? Heartworm disease is a serious and potentially fatal condition caused by parasitic worms living in the arteries of the lungs and in the right side of the heart of dogs, cats and other species of mammals, including wolves, foxes, ferrets, sea lions and (in rare instances) humans. Heartworms are classified as nematodes (roundworms) and are but one of many species of roundworms. The specific roundworm causing heartworm in dogs and cats is known as Dirofilaria immitis. Until recently canine heartworm disease was considered to be a problem only in warm climates, but in the past few years it has been found in almost all areas of the United States and Canada. Since dogs travel widely with their owners, and infected dogs can carry heartworms for several years, heartworm disease may be a problem anywhere in the nation. Heartworm infection is transmitted by mosquitoes. When a mosquito bites an infected dog, it takes up blood which may contain microfilarae. These incubate in the mosquito for about two weeks, during which they become infective larva. Then, when the mosquito bites another dog, the infective larvae are passed into the second dog, infecting it. The infective larvae migrate through the tissues of the body for 2-3 months. They develop into several stages called L1, L2, and L3 stages. The L1 stage only lasts for 1-2 days. The L2 and L3 stages last for approximately two months. They then enter the heart where they reach adult size approximately 3 months after infecting your pet.
The mosquito is the only natural vector of transmission for canine heartworms, and about 70 species are capable of carrying the disease. As you might expect, heartworm infection is more common in areas where mosquitoes are numerous, and outdoor dogs constantly exposed to mosquitoes are the most frequent victims.
How can I find out if my dog has heart disease? Your veterinarian is your dog’s healthcare expert. Regular veterinary visits are important for early detection of health problems.
Your veterinarian may ask you for specific information about your dog before performing a thorough physical examination. If indicated, blood and urine tests, X-rays, an EKG or other tests may be ordered. Regular testing is important for early detection of heart disease in dogs.
“Too often, dog owners do not take their dogs to visit the veterinarian until they are displaying severe signs of heart failure, and by then it may be too late,” says Dr. Bicknese. “When heart disease is detected in your dog, your veterinarian can recommend a schedule of regular visits and discuss a treatment plan that can help.”
Can dogs with heart disease be treated? Although there is no cure for most heart disease in dogs, new treatments are available. Success of treatment depends on various factors, but early detection is always best. By following your veterinarian’s recommendations, you can help your dog live a longer, more comfortable life.
