Crimean-Congo hemorrhagic fever

# Overview
Crimean-Congo hemorrhagic fever (CCHF) is a widespread tick-borne viral disease, a zoonosis of domestic animals and wild animals, that may affect humans. The pathogenic virus, especially common in East and West Africa, is a member of the Bunyaviridae family of RNA viruses. Clinical disease is rare in the majority of infected mammals, but commonly severe in infected humans, with a 30% mortality rate. Outbreaks of illness are usually attributed to handling the bodily fluids of infected animals or people.

# Differentiating Crimean-Congo Hemorrhagic Fever from other Diseases
Crimean-Congo hemorrhagic fever should be differentiated from the following diseases:

# Epidemiology
- Sporadic infection of people is usually caused by Hyalomma tick bite.
- Clusters of illness typically appear after people treat, butcher, or eat infected livestock. Particularly ruminants and ostriches.
- Outbreaks have occurred in clinical facilities where health workers have been exposed to infected blood and fomites.
- On July 28, 2005 authorities reported 41 cases of CCHF in Turkey's Yozgat Province, with one death.

## Endemic Regions
- Endemic areas include Asia, Eastern Europe, the Middle East, a belt across central Africa and South Africa and Madagascar.
- Main environmental reservoir for the virus are small mammals (particularly European hare, Middle-African hedgehogs and multimammate rats).

## Notable outbreaks
- During the summers of 1944 and  over 200 cases of an acute, hemorrhagic, febrile illness occurred in Soviet troops rescuing the harvest following the ethnic cleansing of the Crimean Tatars.
- Virus was discovered in blood samples of patients and in the tick Hyalomma marginatum marginatum.
- Researchers soon recognized that a similar disease had been occurring in the Central Asian Republics.

# Causes

## Life Cycle and Spread of Disease
General Tick Life Cycle 
- A tick's life cycle is composed of four stages: hatching (egg), nymph (six legged), nymph (eight legged), and an adult.
- Ticks require blood meal to survive through their life cycle.
- Hosts for tick blood meals include mammals, birds, reptiles, and amphibians. Ticks will most likely transfer between different hosts during the different stages of their life cycle.
- Humans are most often targeted during the nymph and adult stages of the life cycle.
- Life cycle is also dependent on seasonal variation.
- Ticks will go from eggs to larva during the summer months, infecting bird or rodent host during the larval stage.
- Larva will infect the host from the summer until the following spring, at which point they will progress into the nymph stage.
- During the nymph stage, a tick will most likely seek a mammal host (including humans).
- A nymph will remain with the selected host until the following fall at which point it will progress into an adult.
- As an adult, a tick will feed on a mammalian host. However unlike previous stages, ticks will prefer larger mammals over rodents.
- The average tick life cycle requires three years for completion.
Different species will undergo certain variations within their individual life cycles.
- Different species will undergo certain variations within their individual life cycles.

## Spread of Tick-borne Disease
- Ticks require blood meals in order to progress through their life cycles.
- The average tick requires 10 minutes to 2 hours when preparing a blood meal.
- Once feeding, releases anesthetic properties into its host, via its saliva.
- A feeding tube enters the host followed by an adhesive-like substance, attaching the tick to the host during the blood meal.
- A tick will feed for several days, feeding on the host blood and ingesting the host's pathogens.
- Once feeding is completed, the tick will seek a new host and transfer any pathogens during the next feeding process. 

## Virology
- Nairovirus in the family of Bunyaviridae.

## Transmission
- Ixodid ticks, of the Hyalomma genus, are the primary vector and reservoir of infection.
- Human transmission occurs through human contact with infected animal or human blood and body fluids.

# History and Symptoms
- Typically, after a 13 day incubation period following a tick bite (56 days after exposure to infected blood or tissues), flu-like symptoms appear, which may resolve after one week.
- In up to 75% of cases, however, signs of hemorrhage appear within 35 days of the onset of illness: first mood instability, agitation, mental confusion and throat petechiae, then soon nosebleeds, bloody urine and vomiting, and black stools.
- The liver becomes swollen and painful.
- Disseminated intravascular coagulation may occur as well as acute kidney failure and shock, and sometimes acute respiratory distress syndrome.
- Patients usually begin to recover after 910 days from symptom onset, but 30% die in the second week of illness.

# Laboratory diagnostics
- ELISA, RT-PCR, antibody titers, immunohistochemical staining, and virus isolation attempts are all laboratory tests to assist in the diagnosis of a potential Crimean-Congo hemorrhagic fever.
- An ELISA may be used for diagnosis during the acute phase of infection.
- Polymerase Chain Reaction may be used to identify viral RNA sequences in the blood or tissues collected.

# Treatment
- Treatment is primarily symptomatic and supportive, as there is no established specific treatment.
- Ribavirin is effective in vitro and has been used during outbreaks, but there is no trial evidence to support its use.

# Risk Factors

## Endemic Areas
- Travelling through endemic areas increase the risk of infection.
- Endemic areas include Asia, Eastern Europe, the Middle East, a belt across central Africa and South Africa and Madagascar.

## Livestock
- Sheep, goats and cattle develop high titers of virus in blood, but tend not to fall ill.
- Transmission may occur through unprotected contact with blood and other body fluids of an infected animal.

## Occupational
- The following individuals are at a higher risk of infection in endemic areas:
- Livestock workers
- Animal herders
- Slaughterhouse workers

# Prevention

## Limiting tick exposure
It is unreasonable to assume that a person can completely eliminate activities that may result in tick exposure. Therefore, prevention measures should emphasize personal protection when exposed to natural areas where ticks are present:
- Wear light-colored clothing which allows you to see ticks that are crawling on your clothing.
- Tuck your pants legs into your socks so that ticks cannot crawl up the inside of your pants legs.
- Apply repellents to discourage tick attachment. Repellents containing permethrin can be sprayed on boots and clothing, and will last for several days. Repellents containing DEET (n, n-diethyl-m-toluamide) can be applied to the skin, but will last only a few hours before reapplication is necessary. Use DEET with caution on children.  Application of large amounts of DEET on children has been associated with adverse reactions.
- Conduct a body check upon return from potentially tick-infested areas by searching your entire body for ticks. Use a hand-held or full-length mirror to view all parts of your body. Remove any tick you find on your body.
- Parents should check their children for ticks, especially in the hair, when returning from potentially tick-infested areas.
- Ticks may also be carried into the household on clothing and pets and only attach later, so both should be examined carefully to exclude ticks.

## Public health measures
- Where mammal and tick infection is common agricultural regulations require de-ticking farm animals before transportation or delivery for slaughter.
- Personal tick avoidance measures are recommended, such as use of insect repellents, adequate clothing and body inspection for adherent ticks.
- When feverish patients with evidence of bleeding require resuscitation or intensive care, body substance isolation precautions should be taken.
- The United States armed forces maintain special stocks of ribavirin to protect personnel deployed to Afghanistan and Iraq from CCHF.