Colorado tick fever

Colorado Tick Fever (CTF) (also called Mountain tick fever, Mountain fever, and American mountain fever) is an acute viral infection transmitted from the bite of an infected wood tick (Dermacentor andersoni). It should not be confused with the bacterial tick-borne infection, Rocky Mountain Spotted Fever. The type species of the genus Coltivirus, Colorado tick fever virus (CTFV) infects haemopoietic cells, particularly erythrocytes, which explains how the virus is trasmitted by bloodsucking ticks and also accounts for the incidence of transmission via blood transfusion. The disease develops from March to September, with the highest infections occurring in May and June. The disease is found almost exclusively in the western United States and Canada, mostly in high mountain areas such as Colorado and Idaho. The CTFV was first isolated from human blood in 1944.

The virus particle, like other Coltiviruses, is ~80 nm in diameter and is generally non-enveloped. The double stranded RNA viral genome is ~20,000bp long and is divided into 12 segments, which are termed Seg-1 to Seg-12. Viral replication in infected cells is associated with characteristic cytoplasmic granular matrices. Evidence suggests that viral presence in mature erythrocytes is a result of replication of the virus in hematopoitic erythrocyte precursor cells and simultaneous maturation of the infected immature cells rather than off direct entry and replication of CTFV in mature erythrocytes.

The wood tick is usually found attached to a host, but when it is without a host it hides in cracks and crevices as well as soil. If for some reason the tick is not able to find a host before the winter months, it will stay under groundcover until spring when it can resume its search. The wood tick typically does not seek out available hosts in the hottest summer months as well. Adult ticks, for the most part, tend to climb to the top of grass and low shrubs to attach themselves to a host that is wandering by. These ticks are able to attach to their hosts by secreting a cement-like substance from their mouths and inserting it into the host.

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.

First signs of symptoms can occur about 3-6 days after the initial tick bite, although it can have incubation periods of up to 20 days. Patients usually experience a two-staged fever and illness which can continue for three days, diminish, and then return for another episode of 1-3 days. The virus has the ability to live in the blood stream for up to 120 days; therefore coming in contact without proper precautions and the donation of blood are prohibited.

Initial symptoms include: fever, chills, headaches, pain behind the eyes, light sensitivity, muscle pain, generalized malaise abdominal pain, nausea, vomiting as well as a flat or pimply rash. During the second phase of the virus a high fever can return with an increase in symptoms. CTF can be very severe in cases involving children and have even required hospitalization. Complications with this disease have included aseptic meningitis, encephalitis, and hemorrhagic fever, but these are rare.

CTF is seasonal, mostly occurring in the Rocky Mountain region of the United States and usually in altitudes from 4,000 to 10,000 feet. Patients with CTF are mostly campers and young males, who most likely have been bitten because of their occupational activities.

Diagnosis

A combination of clinical signs, symptoms and laboratory tests can confirm the likelihood of having CTF. Some tests include complement fixation to Colorado tick virus, Immunofluoresence for Colorado tick fever, and some other common laboratory findings suggestive of CTF including leucopenia, thrombocytopenia, and mildly elevated liver enzyme levels.

At this time there is no specific treatment for CTF. The first thing to do is make sure the tick is fully removed from the skin, then Acetaminophen and analgesics can be used to help relieve the fever and pain. Aspirin is not recommended for children it has been linked to Reye’s syndrome in some viral illnesses. Salicylates should not be used because of thrombocytopenia, and the rare occurrence of bleeding disorders. Someone who suspects that they have been bitten by a tick or is starting to show signs of CTF should contact their physician immediately.

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 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. This should be performed with great care.

A match or flame should NOT be used to remove a tick. This method, once thought safe, can cause the tick to regurgitate expelling any disease it may be carrying into the bite wound.

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.

Contracting the CTF virus is thought to provide long lasting immunity against reinfection. However it is always wise to be on the safe side and try to prevent tick bites.

References

• Attoui, H; Billoir F; Biagini P; Cantaloube JF; de Chesse R; de Micco P; de Lamballerie X "Sequence determination and analysis of the full-length genome of Colorado tick fever virus, the type species of genus Coltivirus (Family Reoviridae)". Biochem Biophys Res Commun 273 (3): 1121–5.
• Attoui, H; Jaafar, FM; de Micco, P; de Lamballerie, X. (2005). "Coltiviruses and seadornaviruses in North America, Europe, and Asia". Emerg Infect Dis. 11 (11): 1673–9.
• Edlow, A; Jonathan, MD (2005). Tick-Borne Diseases. Colorado:
• Leiby, DA; Gill, JE. (2004). "Transfusion-transmitted tick-borne infections: a cornucopia of threats". Transfus Med Rev. 18 (4): 293–306.
• Phillip, Claire S.; et al. (1993). "Replication of Colorado tick fever virus within human hematopoietic progenitor cells.". Journal of Virology 67 (4): 2389–2395.
• Smith, Scott D., M.D.,MSc,DTM&H. (2006). Medical Encyclopedia: Colorado tick fever.
• Acute and Communicable Disease Prevention. .
• Rocky Mountain wood tick. .