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Colorado tick fever

In medicine Colorado Tick Fever is an illness caused by a virus of the Reovirus family carried by small mammals, such as ground squirrels, porcupines, and chipmunks, and by ticks. more...

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Anyone who lives or travels in areas of the western United States and Canada at elevations above 5000 feet and who comes in contact with infected ticks, especially Dermacentor andersoni, also known as the wood tick, can get Colorado Tick Fever.

Transmission

Colorado Tick Fever is acquired by tick bite. There is no evidence of natural person-to-person transmission. However, rare cases of transmission from blood transfusions have been reported. The virus which causes Colorado Tick Fever may stay in the blood for as long as four months after onset of the illness.

Symptoms

The disease causes fever of about 103 degrees Fahrenheit, chills, nausea, and severe headache. These symptoms usually last a few days, go away, and then return for a few days. Sometimes the symptoms include a red, raised rash as well as the desire to avoid sun light.

The symptoms generally begin 4 to 5 days after being bitten by an infected tick.

Removing ticks

Ticks should be removed promptly and carefully with tweezers and by applying gentle steady traction. the tick's body should not be crushed when it is removed and and the tweezers should be placed as close to the skin as possible to avoid leaving tick mouth parts in the skin. Ticks should not be removed with bare hands. Hands should be protected by gloves and/or tissues and thoroughly washed with soap and water after the removal process.

Prevention

To avoid tick bites and infection, experts advise:

  • Avoid tick infested areas, especially during the warmer months.
  • Wear light colored clothing so ticks can be easily seen. Wear a long sleeved shirt, hat, long pants, and tuck pant legs into socks.
  • Walk in the center of trails to avoid overhanging grass and brush.
  • Check your body every few hours for ticks when you spend a lot of time outdoors in tick infested areas. Ticks are most often found on the thigh, arms, underarms and legs. Ticks can be very small (no bigger than a pinhead). Look carefully for new "freckles".
  • Use insect repellents containing DEET on your skin or permethrin on clothing. Be sure to follow the directions on the container and wash off repellents when going indoors.
  • Remove attached ticks immediately.

Read more at Wikipedia.org


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Encephalitis
From Gale Encyclopedia of Medicine, 4/6/01 by Richard Robinson

Definition

Encephalitis is an inflammation of the brain, usually caused by a direct viral infection or a hypersensitivity reaction to a virus or foreign protein. Brain inflammation caused by a bacterial infection is sometimes called cerebritis. When both the brain and spinal cord are involved, the disorder is called encephalomyelitis. An inflammation of the brain's covering, or meninges, is called meningitis.

Description

Encephalitis is an inflammation of the brain. The inflammation is a reaction of the body's immune system to infection or invasion. During the inflammation, the brain's tissues become swollen. The combination of the infection and the immune reaction to it can cause headache and a fever, as well as more severe symptoms in some cases.

Approximately 2000 cases of encephalitis are reported to the Centers for Disease Control in Atlanta, GA each year. The viruses causing primary encephalitis can be epidemic or sporadic. The polio virus is an epidemic cause. Arthropod-borne viral encephalitis is responsible for most epidemic viral encephalitis. The viruses live in animal hosts and mosquitos that transmit the disease. The most common form of non-epidemic or sporadic encephalitis is caused by the herpes simplex virus, type 1 (HSV-1) and has a high rate of death. Mumps is another example of a sporadic cause.

Causes & symptoms

Causes

There are more than a dozen viruses that can cause encephalitis, spread by either human-to human contact or by animal bites. Encephalitis may occur with several common viral infections of childhood. Viruses and viral diseases that may cause encephalitis include:

  • Chickenpox
  • Measles
  • Mumps
  • Epstein-Barr virus (EBV)
  • Cytomegalovirus infection
  • HIV
  • Herpes simplex
  • Herpes zoster (shingles)
  • Herpes B
  • Polio
  • Rabies
  • Mosquito-borne viruses (arboviruses).

Primary encephalitis is caused by direct infection by the virus, while secondary encephalitis is due to a post-infectious immune reaction to viral infection elsewhere in the body. Secondary encephalitis may occur with measles, chickenpox, mumps, rubella, and EBV. In secondary encephalitis, symptoms usually begin 5-10 days after the onset of the disease itself and are related to the breakdown of the myelin sheath that covers nerve fibers.

In rare cases, encephalitis may follow vaccination against some of the viral diseases listed above. Creutzfeldt-Jakob disease, a very rare brain disorder caused by an infectious particle called a prion, may also cause encephalitis.

Mosquitoes spread viruses responsible for equine encephalitis (eastern and western types), St. Louis encephalitis, California encephalitis, and Japanese encephalitis. Lyme disease, spread by ticks, can cause encephalitis, as can Colorado tick fever. Rabies is most often spread by animal bites from dogs, cats, mice, raccoons, squirrels, and bats and may cause encephalitis.

Equine encephalitis is carried by mosquitoes that do not normally bite humans but do bite horses and birds. It is occasionally picked up from these animals by mosquitoes that do bite humans. Japanese encephalitis and St. Louis encephalitis are also carried by mosquitoes. The risk of contracting a mosquito-borne virus is greatest in mid- to late summer, when mosquitoes are most active, in those rural areas where these viruses are known to exist. Eastern equine encephalitis occurs in eastern and southeastern United States; western equine and California encephalitis occur throughout the West; and St. Louis encephalitis occurs throughout the country. Japanese encephalitis does not occur in the United States, but is found throughout much of Asia. The viruses responsible for these diseases are classified as arbovirus and these diseases are collectively called arbovirus encephalitis.

Herpes simplex encephalitis, the most common form of sporadic encephalitis in western countries, is a disease with significantly high mortality. It occurs in children and adults and both sides of the brain are effected. It is theorized that brain infection is caused by the virus moving from a peripheral location to the brain via two nerves, the olfactory and the trigeminal (largest nerves in the skull).

Herpes simplex encephalitis is responsible for 10% of all encephalitis cases and is the main cause of sporadic, fatal encephalitis. In untreated patients, the rate of death is 70% while the mortality is 15-20% in patients who have been treated with acyclovir. The symptoms of herpes simplex encephalitis are fever, rapidly disintegrating mental state, headache, and behavioral changes.

Symptoms

The symptoms of encephalitis range from very mild to very severe and may include:

  • Headache
  • Fever
  • Lethargy (sleepiness, decreased alertness, and fatigue)
  • Malaise
  • Nausea and vomiting
  • Visual disturbances
  • Tremor
  • Decreased consciousness (drowsiness, confusion, delirium, unconsciousness)
  • Stiff neck
  • Seizures.

Symptoms may progress rapidly, changing from mild to severe within several days or even several hours.

Diagnosis

Diagnosis of encephalitis includes careful questioning to determine possible exposure to viral sources. Tests which can help confirm the diagnosis and rule out other disorders include:

  • Blood tests. These are to detect antibodies to viral antigens, and foreign proteins.
  • Cerebrospinal fluid analysis (spinal tap). This detects viral antigens, and provides culture specimens for the virus or bacteria that may be present in the cerebrospinal fluid.
  • Electroencephalogram (EEG)
  • CT and MRI scans.

A brain biopsy (surgical gathering of a small tissue sample) may be recommended in some cases where treatment to date has been ineffective and the cause of the encephalitis is unclear. Definite diagnosis by biopsy may allow specific treatment that would otherwise be too risky.

Treatment

Choice of treatment for encephalitis will depend on the cause. Bacterial encephalitis is treated with antibiotics. Viral encephalitis is usually treated with antiviral drugs including acyclovir, ganciclovir, foscarnet, ribovarin, and AZT. Viruses that respond to acyclovir include herpes simplex, the most common cause of sporadic (non-epidemic) encephalitis in the United States.

The symptoms of encephalitis may be treated with a number of different drugs. Corticosteroids, including prednisone and dexamethasone, are sometimes prescribed to reduce inflammation and brain swelling. Anticonvulsant drugs, including dilantin and phenytoin, are used to control seizures. Fever may be reduced with acetaminophen or other fever-reducing drugs.

A person with encephalitis must be monitored carefully, since symptoms may change rapidly. Blood tests may be required regularly to track levels of fluids and salts in the blood.

Prognosis

Encephalitis symptoms may last several weeks. Most cases of encephalitis are mild, and recovery is usually quick. Mild encephalitis usually leaves no residual neurological problems. Overall, approximately 10% of those with encephalitis die from their infections or complications such as secondary infection. Some forms of encephalitis have more severe courses, including herpes encephalitis, in which mortality is 15-20% with treatment, and 70-80% without. Antiviral treatment is ineffective for eastern equine encephalitis, and mortality is approximately 30%.

Permanent neurological consequences may follow recovery in some cases. Consequences may include personality changes, memory loss, language difficulties, seizures, and partial paralysis.

Prevention

Because encephalitis is due to infection, it may be prevented by avoiding the infection. Minimizing contact with others who have any of the viral illness listed above may reduce the chances of becoming infected. Most infections are spread by hand-to-hand or hand-to-mouth contact; frequent hand washing may reduce the likelihood of infection if contact cannot be avoided.

Mosquito-borne viruses may be avoided by preventing mosquito bites. Mosquitoes are most active at dawn and dusk, and are most common in moist areas with standing water. Minimizing exposed skin and use of mosquito repellents on other areas can reduce the chances of being bitten.

Vaccines are available against some viruses, including polio, herpes B, Japanese encephalitis, and equine encephalitis. Rabies vaccine is available for animals; it is also given to people after exposure. Japanese encephalitis vaccine is recommended for those traveling to Asia and staying in affected rural areas during transmission season.

Key Terms

Cerebrospinal fluid analysis
A analysis that is important in diagnosing diseases of the central nervous system. The fluid within the spine will indicate the presence of viruses, bacteria, and blood. Infections such as encephalitis will be indicated by an increase of cell count and total protein in the fluid.

Computerized tomography (CT)
A test to examine organs within the body and detect evidence of tumors, blood clots, and accumulation of fluids.
Electroencephalagram (EEG)
A chart of the brain waves picked up by the electrodes placed on the scalp. Changes in brain wave activity can be an indication of nervous system disorders.
Inflammation
A response from the immune system to an injury. The signs are redness, heat, swelling and pain.
Magnetic Resonance Imaging (MRI)
MRI is diagnostic radiography using electromagnetic energy to create an image of the central nervous system (CNS), blood system, and musculoskeletal system.
Vaccine
A prepartation containing killed or Henvated (weakened) microorganisms used to build immunity against infection from that microorganism.
Virus
A very small organism that can only live within a cell. They are unable to reproduce outside that cell.

Further Reading

For Your Information

    Books

  • Harrison's Principles of Internal Medicine, 14th ed., edited by Anthony S. Fauci. McGraw-Hill, 1997.
  • Hurst, J. Willis. Medicine for the Practicing Physician. Stamford, CT: Appleton and Lange.
  • Samuels, Martin, and Steven Feske. Office Practice of Neurology. New York: Churchill Livingstone, 1996.
  • The Merck Manual. Whitehouse Station, NJ: Merck and Co. Inc., 1996-1997.

    Organizations

  • Centers for Disease Control and Prevention. 1600 Clifton Rd., NE, Atlanta, GA 30333. 404-639-3311. http://www.cdc.gov.

Gale Encyclopedia of Medicine. Gale Research, 1999.

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