LaCrosse Encephalitis:

We would like to acknowledge and thank the Centers for Disease Control for allowing
the use of the following information and links concerning mosquito-borne illness.

LaCrosse Encephalitis Facts & Information:

CLINICAL FEATURES:

• Frank encephalitis progressing to seizures, coma; majority of infections are subclinical or result in mild illness

ETIOLOGIC AGENT :

• La Crosse virus - California serogroup virus in the family Bunyaviridae

INCIDENCE:

• Approximately 70 cases reported per year

SEQUELAE:

• Case-fatality ratio <1%
• Hospitalization for CNS infection
• Neurological sequelae that resolve within several years

COSTS:

• Short-term hospitalization to long-term care exceeding $450,000
• Social costs from adverse effects on IQ and school performance

TRANSMISSION:

• Virus cycles in woodland habitats between the treehole mosquito (Aedes triseriatus) and vertebrate hosts (chipmunks, squirrels)
• Virus survives winter in mosquito
• Vector uses artificial containers (tires, buckets, etc.) in addition to treeholes

RISK GROUPS:

• Children <16 years old: biological risk factor
• Residence in woodland habitats environmental risk factor
• Containers at residence environmental risk factor
• Outdoor activities: behavioral risk factor

SURVEILLANCE:

• Active case surveillance in collaboration with state and local health departments, and mosquito control districts

TRENDS:

• Traditional endemic foci in the great-Lakes states
• Increased case incidence in mid-Atlantic states
• Rural poor most affected

CHALLENGES:

• Multiple environmental, biological and social factors contributing to disease occurrence
• Disease is considerably under-reported
• No vaccine available

Rift Valley Fever:

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the use of the following information and links concerning mosquito-borne illness.

Rift Valley Fever Questions & Answers:

Q. What is Rift Valley fever?

A. Rift Valley fever (RVF) is an acute, fever-causing viral disease that affects domestic animals (such as cattle, buffalo, sheep, goats, and camels) and humans. RVF is most commonly associated with mosquito-borne epidemics during years of unusually heavy rainfall.

The disease is caused by the RVF virus, a member of the genus Phlebovirus in the family Bunyaviridae. The disease was first reported among livestock by veterinary officers in Kenya in the early 1900s.

Q. Where is Rift Valley Fever found?

A. RVF is generally found in regions of eastern and southern Africa where sheep and cattle are raised, but the virus also exists in most countries of sub-Saharan Africa and in Madagascar. In September 2000, a RVF outbreak was reported in Saudi Arabia and subsequently Yemen. These cases represent the first Rift Valley fever cases identified outside Africa.

RVF virus primarily affects livestock and can cause disease in a large number of domestic animals (this situation is referred to as an "epizootic"). The presence of an RVF epizootic can lead to an epidemic among humans who are exposed to diseased animals. The most notable epizootic of RVF, which occurred in Kenya in 1950-1951, resulted in the death of an estimated 100,000 sheep. In 1977, the virus was detected in Egypt (probably exported there in infected domestic animals from Sudan) and caused a large outbreak of RVF among animals and humans. The first epidemic of RVF in West Africa was reported in 1987 and was linked to construction of the Senegal River Project. The project caused flooding in the lower Senegal River area and altered interactions between animals and humans resulting in transmission of the RVF virus to humans.

Q. How is RVF virus spread among animals?

A. An epizootic of RVF is generally observed during years in which unusually heavy rainfall and localized flooding occur. The excessive rainfall allows mosquito eggs, usually of the genus Aedes, to hatch. The mosquito eggs are naturally infected with the RVF virus, and the resulting mosquitoes transfer the virus to the livestock on which they feed. Once the livestock is infected, other species of mosquitoes can become infected from the animals and can spread the disease. In addition, it is possible that the virus can be transmitted by other biting insects.

Q. How do humans get RVF?

A. Humans can get RVF as a result of bites from mosquitoes and possibly other bloodsucking insects that serve as vectors. Humans can also get the disease if they are exposed to either the blood or other body fluids of infected animals. This exposure can result from the slaughtering or handling of infected animals or by touching contaminated meat during the preparation of food. Infection through aerosol transmission of RVF virus has resulted from contact with laboratory specimens containing the virus.

Q. What are the symptoms of RVF?

A. RVF virus can cause several different disease syndromes. People with RVF typically have either no symptoms or a mild illness associated with fever and liver abnormalities. However, in some patients the illness can progress to hemorrhagic fever (which can lead to shock or hemorrhage), encephalitis (inflammation of the brain, which can lead to headaches, coma, or seizures), or ocular disease (diseases affecting the eye). Patients who become ill usually experience fever, generalized weakness, back pain, dizziness, and extreme weight loss at the onset of the illness. Typically, patients recover within two days to one week after onset of illness.

Q. Are there complications after recovery?

A. The most common complication associated with RVF is inflammation of the retina (a structure connecting the nerves of the eye to the brain). As a result, approximately 1% - 10% of affected patients may have some permanent vision loss.

Q. Is the disease ever fatal?

A. Approximately 1% of humans that become infected with RVF die of the disease. Case-fatality proportions are significantly higher for infected animals. The most severe impact is observed in pregnant livestock infected with RVF, which results in abortion of virtually 100% of fetuses.

Q. How is RVF treated?

A. There is no established course of treatment for patients infected with RVF virus. However, studies in monkeys and other animals have shown promise for ribavirin, an antiviral drug, for future use in humans. Additional studies suggest that interferon, immune modulators, and convalescent-phase plasma may also help in the treatment of patients with RVF.

Q. Who is at risk for the illness?

A. Studies have shown that sleeping outdoors at night in geographical regions where outbreaks occur could be a risk factor for exposure to mosquito and other insect vectors. Animal herdsmen, abattoir workers, and other individuals who work with animals in RVF-endemic areas (areas where the virus is present) have an increased risk for infection. Persons in high-risk professions, such as veterinarians and slaughterhouse workers, have an increased chance of contracting the virus from an infected animal. International travelers increase their chances of getting the disease when they visit RVF-endemic locations during periods when sporadic cases or epidemics are occurring.

Q. How is RVF prevented?

A. A person's chances of becoming infected can be reduced by taking measures to decrease contact with mosquitoes and other bloodsucking insects through the use of mosquito repellents and bednets. Avoiding exposure to blood or tissues of animals that may potentially be infected is an important protective measure for persons working with animals in RVF-endemic areas.

Q. What needs to be done to address the threat of RVF?

A. A number of challenges remain for the control and prevention of RVF. Knowledge regarding how the virus is transmitted among mosquitoes and the role of vertebrates in propagating the virus must be answered to predict and control future outbreaks of RVF. Vaccines for veterinary use are available, but they can cause birth defects and abortions in sheep and induce only low-level protection in cattle. The human live attenuated vaccine, MP-12, has demonstrated promising results in laboratory trials in domestic animals, but more research will be needed before the vaccine can be used in the field. In addition, surveillance (close monitoring for RVF infection in animal and human populations) is essential to learning more about how RVF virus infection is transmitted and to formulate effective measures for reducing the number of infections.

Yellow Fever:

We would like to acknowledge and thank the Centers for Disease Control for allowing
the use of the following information and links concerning mosquito-borne illness.

Yellow Fever Facts:

Though Yellow Fever is currently only found in Africa and South America, it still greatly impacts those areas and is an issue of consideration for anyone traveling to regions that have a history of Yellow Fever. Fever is a flavivirus and is transmitted by the Yellow Fever mosquito, Aedes aegypti. For over 60 years there has been an effective vaccine available, but even so, the cases of Yellow Fever have been increasing.

Infection with the Yellow Fever virus will not have any symptoms for three to six days. Some people infected will continue to show no, or minimal symptoms to the infection. Most cases however will experience the “acute phase” of the disease, which is characterized by fever, muscle pain, headache, shivers, loss of appetite, nausea and/or vomiting. This phase typically last three to four days and most cases will then make recovery.

Fifteen percent of infections will continue from the 'acute phase' into the 'toxic phase'. This occurs within 24 hours as the disease is affecting the body quickly and severely. Rapid development of jaundice (yellowing of the skin and whites of the eyes) occurs along with fever, abdominal pain and vomiting. Bleeding from the mouth, nose, eyes and/or stomach can accompany this phase and will lead to blood appearing in the vomit and feces. This characteristic of Yellow Fever is attributed with one of its common names, Black Vomit. Deterioration of kidney function follows, though this can be minor to complete kidney failure. 50% of the patients that enter the 'toxic phase' will die within 10-14 days. For those whom survive, it is without significant organ damage.

Yellow Fever is hard to identify and diagnose, so underreporting undoubtedly occurs. It is estimated that there are about 200,000 cases, with 30,000 deaths occurring, annually from Yellow Fever.

Though there is not any specific treatment of this disease there is a safe and effective vaccine. The vaccine provides immunity in about one week for 95% of people vaccinated and is effective for 10 years (and possibly provides lifelong protection).

Continuing Risk:

In some areas of Africa and South America the virus is constantly present at an endemic stage (low level of infection) and the virus can regularly amplify into epidemic levels. Since the 1900s, outbreaks of Yellow Fever have not occurred in Europe, the Caribbean Islands, or Central and North America. But history has shown that these regions have seen outbreaks before and experience indicates that the potential for future outbreaks still do exist.