Prevalence and Incidence of West Nile fever
West Nile fever: Rare Disease
West Nile fever is listed as a "rare disease" by the Office of
Rare Diseases (ORD) of the National Institutes of Health
(NIH). This means that West Nile fever, or a subtype of West Nile fever,
affects less than 200,000 people in the US population.
West Nile fever Prevalence: Book Excerpts
Prevelance of West Nile fever discussion:
In 1999, 62 cases of severe disease, including 7 deaths, occurred
in the New York area. In 2000, 21 cases were reported, including 2 deaths
in the New York City area. In 2001, there were 66 human cases of
severe disease and 9 deaths. No reliable estimates are available for the
number of cases of West Nile encephalitis that occur worldwide. (Source: excerpt from West Nile Virus Questions and Answers: DVBID)
Prevalence/Incidence of West Nile fever: Online Medical Books
16 MEDICAL BOOKS ONLINE!
Review excerpts from medical books online, free, without registration,
for more information about the prevalence and/or incidence of West Nile fever.
West Nile encephalitis:
Causes and incidence
(Professional Guide to Diseases (Eighth Edition))
WNV is transmitted to humans by the bite of a mosquito (primarily the Culex species) infected with the virus. It's considered the primary vector for WNV and the source of the August 1999 outbreak in New York, New Jersey and Connecticut. Mosquitoes become infected by feeding on birds contaminated with the West Nile virus and then transmitting it to humans and animals during a blood meal or “bite.” (See Transmission routes of West Nile virus, page 256.)
Ticks have been found infected with WNV in Africa and Asia only. The role of ticks in the transmission and maintenance of the virus remains uncertain, and to date they aren't considered vectors for WNV in the United States.
The Centers for Disease Control and Prevention has reported that there is no evidence that a person can contract the virus from handling live or dead infected birds. However, avoid barehanded contact when handling dead animals, including birds, and use gloves or double plastic bags to dispose of a carcass. Report the finding to the local health department.
» READ BOOK EXCERPT ONLINE »
Source: Professional Guide to Diseases (Eighth Edition), 2005
Colorado tick fever:
Causes and incidence
(Professional Guide to Diseases (Eighth Edition))
Colorado tick fever is transmitted to humans by a hard-shelled wood tick called Dermacentor andersoni. The adult tick acquires the virus when it bites infected rodents and remains permanently infective.
Incidence is high in Colorado, where up to 15% of people who regularly camp show past exposure. It's much less common in the rest of the United States.
» READ BOOK EXCERPT ONLINE »
Source: Professional Guide to Diseases (Eighth Edition), 2005
Lassa fever:
Causes and incidence
(Professional Guide to Diseases (Eighth Edition))
A chronic infection in rodents, Lassa virus is transmitted to humans by contact with infected rodent urine, feces, and saliva. The virus enters the bloodstream, lymph vessels, and respiratory and digestive tracts. It then multiplies in the cells of the reticuloendothelial system. In the early stages of this illness, when the virus is in the throat, human transmission may occur through inhalation of infected droplets.
As many as 100 cases of Lassa fever occur annually in western Africa; the disease is rare in the United States.
» READ BOOK EXCERPT ONLINE »
Source: Professional Guide to Diseases (Eighth Edition), 2005
Relapsing fever:
Causes and incidence
(Professional Guide to Diseases (Eighth Edition))
The body louse (Pediculus humanus corporis) carries louse-borne relapsing fever (B. recurrentis), which typically occurs in epidemics during wars, famines, and mass migrations. Cold weather and crowded living conditions also favor the spread of body lice.
Inoculation takes place when the victim crushes the louse, causing its infected blood or body fluid to soak into the victim's bitten or abraded skin or mucous membranes.
Louse-borne relapsing fever is most common in North and Central Africa, Europe, Asia, and South America. No cases of louse-borne relapsing fever have been reported in the United States since 1900.
Tick-borne relapsing fever, however, is found in the United States and is caused by at least 15 Borrelia species; the three species most commonly identified with tick carriers are B. hermsii (associated with Ornithodoros hermsi), B. turicatae (associated with O. turicata), and B. parkeri (associated with O. parkeri). This form of the disease is most prevalent in Texas and other western states, usually during the summer when ticks and their hosts (chipmunks, goats, squirrels, rabbits, mice, rats, owls, lizards, and prairie dogs) are most active. In the colder weather, outbreaks sometimes afflict people such as campers who sleep in tick-infested cabins.
Because tick bites are virtually painless and most Ornithodoros ticks feed at night but don’t imbed themselves in the victim’s skin, many people are bitten unknowingly.
» READ BOOK EXCERPT ONLINE »
Source: Professional Guide to Diseases (Eighth Edition), 2005
Rheumatic fever and rheumatic heart disease:
Causes and incidence
(Professional Guide to Diseases (Eighth Edition))
Rheumatic fever appears to be a hypersensitivity reaction to a group A beta-hemolytic streptococcal infection, in which antibodies manufactured to combat streptococci react and produce characteristic lesions at specific tissue sites, especially in the heart and joints. Because very few persons (3%) with streptococcal infections ever contract rheumatic fever, altered host resistance must be involved in its development or recurrence. Although rheumatic fever tends to be familial, this may merely reflect contributing environmental factors. For example, in lower socioeconomic groups, incidence is highest in children between ages 5 and 15, probably as a result of malnutrition and crowded living conditions. This disease strikes generally during cool, damp weather in the winter and early spring. In the United States, it’s most common in the northern states.
» READ BOOK EXCERPT ONLINE »
Source: Professional Guide to Diseases (Eighth Edition), 2005
Rocky Mountain spotted fever:
Causes and incidence
(Professional Guide to Diseases (Eighth Edition))
R. rickettsii is transmitted to a human or small animal by the prolonged bite (4 to 6 hours) of an adult tick — the wood tick (Dermacentor andersoni) in the west and by the dog tick (Dermacentor variabilis) in the east. Occasionally, it's acquired through inhalation (it can occur in laboratory settings where aerosolization of blood and specimens may occur) or through the contact of abraded skin with tick excreta or tissue juices. (This explains why people should'nt crush ticks between their fingers when removing them from other people and animals.) In most tick-infested areas, 1% to 5% of the ticks harbor R. rickettsii.
Endemic throughout the continental United States, RMSF is particularly prevalent in the southeast and southwest. Because RMSF is associated with outdoor activities, such as camping and backpacking, the incidence of this illness is usually higher in the spring and summer. Epidemiologic surveillance reports for RMSF indicate that the incidence is also higher in children ages 5 to 9, men and boys, and whites.
» READ BOOK EXCERPT ONLINE »
Source: Professional Guide to Diseases (Eighth Edition), 2005
West Nile Virus (And Other Arbovirus Encephalitis):
West Nile Virus - epidemiology
(The 5-Minute Pediatric Consult)
- Arboviruses are spread by mosquitoes, ticks, and sand flies. The major vector for WNV in the United States is the Culex mosquito. WNV has been spread through blood transfusions and transplanted organs.
- Arboviruses are maintained in nature through cycles of transmission among birds, horses, and small animals. Humans and domestic animals are infected incidentally as “dead-end” hosts.
- Disease among birds has been a hallmark of WNV in the US and has served as a sensitive surveillance indicator of WNV activity.
- Each North American arbovirus has specific geographic distributions and is associated with a different ratio of asymptomatic-to-clinical infections. These agents cause disease of variable severity and have distinct age-dependent effects. WNV has now been identified throughout the US and is also found in Europe, Africa, and Asia.
West Nile Virus - incidence
- The peak incidence of arboviral encephalitis occurs during the late summer and early fall. Seasonality depends on the breeding and feeding seasons of the arthropod host.
- WNV is the leading cause of arboviral CNS disease. Encephalitis is most commonly seen in older adults, generally aged >50 years. Cases of WNV in children are unusual.
- A median of 3–5 cases of Western equine encephalitis and Eastern equine encephalitis are reported nationally each year. Eastern equine encephalitis tends to produce a more fulminant illness than LaCrosse or Western equine encephalitis.
» READ BOOK EXCERPT ONLINE »
Source: The 5-Minute Pediatric Consult, 2008
About prevalence and incidence statistics:
The term 'prevalence' of West Nile fever usually refers to the estimated population
of people who are managing West Nile fever at any given time.
The term 'incidence' of West Nile fever refers to the annual diagnosis rate,
or the number of new cases of West Nile fever diagnosed each year.
Hence, these two statistics types can differ:
a short-lived disease like flu can have high annual incidence but low prevalence,
but a life-long disease like diabetes has a low annual incidence but high prevalence.
For more information see about prevalence and incidence statistics.
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