Colorado tick fever virus
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[edit] Background
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) a member of the Coltivirus genera. CTF infects haemopoietic cells especially erythrocytes, which explains how the virus is trasmitted by bloodsicking 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. [1] The disease is found almost exclusively in the western United States and Canada, mostly in high mountain areas such as Colorado and Idaho. The CTF virus was first isolated from human blood in 1944. [2]
The virus particle, like other Coltiviruses, is ~80 nm in diameter and is generally non-envolped. 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 maturationof the infected immature cells rather than off direct entry and replication of CTF virus in mature erythrocytes.[3]
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.[4]
[edit] Behavior/Reproductive
Adult ticks tend to feed for less than an hour at a time. Their primary food source is terrestrial birds, reptiles, and mammals. The wood tick goes through three stages (larvae, nymph, and adult), each stage can survive without food for more than a year, except for the beginning 30 days of the larvae cycle. They do require a meal of blood before developing into the next stage. Larvae feed throughout the summer, and the nymphs continue into late summer. Male ticks feed for about five days without engorging, they become sexually mature, begin to mate, and then continue feeding. Females on the other hand feed up to seven days and become engorged, they then begin to mate. The female’s body weight could go from 0.000176 oz to more than 0.0247 oz during the engorging time. The wood tick reproduces once in a lifetime, after which it dies. Mating takes place on the host with the fully engorged female on top of the male. After feeding for 4-17 days the female climbs down from the host and seeks a secure area to lay her eggs. In the spring the female lays a single cluster of anywhere from 2,500-7,400 yellowish brown ellipsoidal eggs over a period of 10-33 days. The female then dies within 1-14 days. During the next 7-38 days the eggs could hatch, as long as the temperature ranges from 72-90 degrees Farenhight.[5]
[edit] Symptoms
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. [6] 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.[7] Patients with CTF are mostly campers and young males, who most likely have been bitten because of their occupational activities.
[edit] Diagnosis
A combination of clinical signs, symptoms and laboratory tests can confirm the likely hood 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.[8]
[edit] Tick Removal
- Use fine-tipped tweezers. When at all possible people should avoid using their hands to remove the tick.
- Grab the tick as close as possible to the exposed skin and pull upward with steady, even pressure. Jerking the tick can cause the mouthparts to break off and remain in the skin.
- Do not squeeze, crush, or puncture the body of the tick because its fluids can contain infectious materials.
- Thoroughly disinfect the bitten area, and wash your hands.
- It is important to save the tick or any remains that you can acquire in case you become ill. Put the tick in a plastic bag with the date of the bite and place it in the freezer.
In all actuality it is not recommended to remove the tick by yourself, because the likelyhood of breaking off parts of the tick are extremlly high.
Here are a few additional tips:
- Light a match and blow it out. Put the hot match head on the tick, this should refrain the tick from burrowing further into the skin and start backing out. Ticks do not like heat applied to them.
- Emmerse the tick and skin in vegetable or cooking oil, this will stop the tick in its tracks. Ticks breath with their back legs, and therfore will have a hard time when they are taking in oil. This should incline the tick to back out immediately.
[edit] Prevention
• Try to wear light colored clothing when walking or hiking. This will allow you to see ticks that are crawling on your clothes.
• Wear long sleeve shirts and tuck your pant legs into your socks.
• Repellants such as permethrin can be sprayed on boots and clothing and will last for days. Repellants containing DEET will only last for a few hours.
• After returning from a tick-infested area, conduct a body search using a mirror.
• Children and pets should be checked for ticks in hidden areas such as hair.
Contacting 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.
[edit] References/Links
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. 2000 Jul 14;273(3):1121-5.
Attoui H, Jaafar FM, de Micco P, de Lamballerie X. Coltiviruses and seadornaviruses in North America, Europe, and Asia. Emerg Infect Dis. 2005 Nov;11(11):1673-9.
Edlow A, Jonathan MD. Tick-Borne Diseases, Colorado. 2005. 8 Oct. 2006 <http://www.emedicine.com/EMERG/topic586.htm>.
Leiby DA, Gill JE. Transfusion-transmitted tick-borne infections: a cornucopia of threats. Transfus Med Rev. 2004 Oct;18(4):293-306.
Phillip, Claire S., et al. "Replication of Colorado tick fever virus within human hematopoietic progenitor cells." Journal of Virology 67.4 (1993): 2389-2395. <http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=240408.
Smith, Scott D., M.D.,MSc,DTM&H. Medical Encyclopedia: Colorado tick fever. 2006. 8 Oct. 2006 <http://www.nlm.nih.gov/medlineplus/print/ency/article/ooo675.htm>.
Acute and Communicable Disease Prevention <http://www.oregon.gov/DHS/ph/acd/diseases/ctf/facts.shtml>.
Rocky Mountain wood tick <http://www.answers.com/topic/rocky-mountain-wood-tick>.
