Chikungunya

What is the Chikungunya

Chikungunya is a disease of viral origin, a zoonosis transmitted to humans through the bite of infected mosquitoes, characterized by acute fever and severe pain in the joints. The infection is caused by a virus belonging to the Togaviridae family, isolated for the first time from the blood of a febrile patient in Tanzania in 1952.

Since then, this pathogen has been reported as the agent responsible for numerous human epidemics, in many areas of Africa and Asia. Recently, in August 2007, the first autochthonous cases in Europe were notified.

"Chikungunya" derives from a word makonde which means "that which bends" or "contorsce", to indicate the curved aspect which assumes who suffers from the serious arthralgia related to it. Chikungunya fever is diagnosed on the basis of symptoms and physical signs, laboratory tests and the possibility that exposure to infected mosquitoes has occurred. Symptoms include muscle pain, headache, nausea, fatigue and rash. Chikungunya fever shares some clinical signs with dengue and can be misdiagnosed in endemic areas where the two viral agents are simultaneously present. There is no specific drug to treat the disease. Treatment is aimed at controlling symptoms.

Infectious agent and vectors

Chikungunya and Aedes mosquitoes viruses

The infection is caused by the Chikungunya virus ( CHIKV ), a single-stranded RNA infectious agent, sensitive to drying, disinfectants and soap.

The virus is transmitted by mosquitoes of the genus Aedes : both the Aedes aegypti, and the Aedes albopictus are implicated in the great epidemics of chikungunya. Both can be identified by the striking white stripes located on their black bodies and legs. Aedes mosquitoes are also involved in the transmission of other diseases, including dengue and yellow fever. The Aedes aegypti mosquito is the primary vector and is confined mainly to tropical and sub-tropical areas. Aedes albopictus, commonly called "tiger mosquito", is also present in temperate regions and is considered responsible for the spread of the virus in Asia, Africa and Europe. The tiger mosquito is also present in the urban areas of our country. Aedes albopictus thrives in a wider range of sites than Aedes aegypti, including coconut husks, cocoa pods, bamboo stumps, tree cavities and natural or artificial water surfaces, such as vehicle tires and saucer dishes some plants. These bloodsucking insects can sting both during the day and at night, with activity peaks in the early morning and late afternoon, indoors or outdoors. In Africa, several other mosquitoes have been indicated as potential vectors for the viral agent.

Contagion

Transmission occurs through the bite of an infected mosquito. The epidemics are supported by the man-mosquito-man transmission. The main reservoirs of the virus are monkeys, but other animals can also be affected, including humans. Mosquitoes come into contact with the virus by pricking infected humans or animals and remain carriers of chikungunya throughout their life cycle. After the bite of an infected mosquito, the onset of the disease occurs after 4-8 days, but the incubation period can vary from 2 to 12 days. The risk that an infected person can transmit the virus to a mosquito is higher when the patient is viremic, ie during the first 2-6 days of the acute phase. Chikungunya fever is not transmissible from human to human, except through direct contact with infected blood. The viremia in humans is not well defined, but it is thought to correspond to the period preceding the immediate onset of symptoms. Maternal-fetal vertical transmission has also been documented and is more likely if the woman is viremic at the time of delivery. CHIKV does not appear to be transmitted via breast milk.

Epidemiology

The endemic basin of the disease is located in different areas of Africa, Asia and India. In recent decades, chikungunya-bearing mosquitoes have also spread to Europe and the Americas.

Since 2004, an onset of an outbreak has been recorded on the coast of Kenya, which has gradually spread to various islands in the Indian Ocean and Asia, causing millions of cases of illness.

The tiger mosquito is responsible for the first chikungunya epidemic in Europe. In the summer of 2007, after the introduction of a viremic traveler returning from India, the native spread (from man to mosquito-man) took place in the north of Italy, during which more than 200 people were infected. Given the great epidemics caused by the virus, the high level of viremia in humans and the worldwide distribution of Aedes aegypti and Aedes albopictus, there is a risk that this disease can spread again. Furthermore, it is evident that the mutations of the Chikungunya virus are transmitted directly and with extreme ease.

The risk to travelers is higher if the destination is an endemic area. Epidemics occur mainly during the tropical rainy season and tend to decrease during the dry season. However, some outbreaks in Africa occurred after periods of drought, in which containers for collecting water also constituted sites of proliferation for carriers.

Symptoms

To learn more: Symptoms Chikungunya

Chikungunya fever is characterized by the sudden appearance of high fever (temperature generally above 39 ° C), often accompanied by joint pain or stiffness. Other common signs and symptoms include muscle pain, headache, nausea, vomiting, muscle pain (muscle pain), fatigue and rash. Acute disease usually lasts from a few days to a week.

Often, the pain is very debilitating. After the onset of fever, in some cases it may develop an itchy rash, typically maculo-papular, which involves the trunk and extremities, but may also include the palms of the hands, soles of the feet and face. Abnormal laboratory findings may include thrombocytopenia, leukopenia and impaired liver function. Furthermore, an important increase in erythrocyte sedimentation rate (ESR) and C-reactive protein is often reported. Approximately 3% -28% of people infected with CHIKV are, instead, asymptomatic. Most patients recover spontaneously within 7-10 days after initial infection, however some patients have reported prolonged fatigue lasting several weeks. In other cases, debilitating joint pain, stiffness or tenosynovitis may persist for several months. Complications are rare, but more common in newborns (65 years) and in people suffering from other chronic diseases, such as diabetes, hypertension, etc. The atypical manifestations of chikungunya include: myocarditis, ocular diseases (uveitis and retinitis), hepatitis, acute renal failure, gastrointestinal disorders, rash (blisters and ulcers) and neurological complications (meningoencephalitis, Guillain-Barré syndrome, paresis or paralysis). Complications can be caused by direct effects of the virus, by the immunological response to the pathogen or by the toxicity of drug therapy.

Chikungunya is not a fatal disease. Deaths related to CHIKV infections are rare: advanced age, immunodepression conditions and the presence of concomitant diseases are likely risk factors for negative outcomes. Pregnant women can be infected during all stages of pregnancy and the onset of chikungunya does not involve transmission of the virus to the fetus. The highest risk of vertical transmission occurs when the woman has viremia at the time of delivery. In these cases, complications may arise for the child, including neurological diseases, bleeding symptoms and heart disease. There are also rare cases of spontaneous abortion that occur after maternal CHIKV infection.

Diagnosis

Preliminary diagnosis of the disease is based on clinical characteristics. In case of fever, especially if associated with joint pain, it is recommended that travelers returning from an endemic area should report to their doctor or hospital the countries they have visited. Different methods are available for clinical diagnosis, with variable sensitivity. The virus can be isolated from the blood during the first days of infection. During the first week after the onset of symptoms, chikungunya fever can be diagnosed by viral culture or amplification of nucleic acids on serum.

Three main types of laboratory tests for the diagnosis of chikungunya we recall:

• Virus isolation : within the first 3 days of illness (during the acute phase). The technique consists in exposing blood samples to specific cell lines to identify virus-specific responses.
• RT-PCR to analyze viral nucleic acid : 1-8 days after the onset of the disease, it allows to amplify different genes of the chikungunya virus (polymerase chain reaction with retro-transcription). The products of clinical samples obtained by RT-PCR can also be used for genotyping the virus and can make it possible to make a comparison with virus samples from various geographical sources.
• Serological tests for IgM / IgG : serological tests, such as the ELISA immunoassay method, can be performed starting from 4 days after infection. These analyzes can confirm the presence of IgM antibodies (produced in the earliest stages of infection) and IgG (late products) aimed at the Chikungunya virus. Virus-specific IgM antibody levels are elevated 3-5 weeks after the onset of the disease and persist for approximately two months.

Treatment

There are no specific antiviral drugs available for chikungunya fever. The goal of therapy consists primarily of controlling and alleviating symptoms , including joint pain. Symptomatic treatment is recommended after the diagnostic exclusion of more serious conditions, such as dengue or other bacterial infections. Therapy may include rest, generous intake of fluids, use of analgesics and antipyretics to lower fever. Symptomatic treatment of pain may include taking ibuprofen, naproxen, acetaminophen or paracetamol, while aspirin is generally avoided. Infected people should be protected indoors, staying in areas protected by a mosquito net, to avoid further exposure to the carrier during the first days of the disease and to avoid the spread of infection.

Acute phase therapy Treatment is symptomatic and supportive: Rest and fluids; NSAIDs (to relieve joint pain). For patients with severe joint pain who do not respond to NSAIDs: Narcotics (for example, morphine); Short-term corticosteroids. These can be used after assessing the risk-benefit ratio of the treatment .

Subacute and chronic disease The convalescence can be prolonged, sometimes more than a year. Persistent pain may require long-term anti-inflammatory therapy. To treat refractory arthritis with other agents: intra-articular corticosteroids or topical NSAIDs.

To learn more: Chikungunya treatment drugs »

Outbreaks of chikungunya fever

Chikungunya fever mainly affects the tropical regions of Africa, India and South-East Asia. The spread of the disease is increasing. Before traveling, it is recommended to inquire about the current disease situation in the destination country.

Prevention

Currently there is no commercial vaccine or a specific drug to prevent chikungunya. The best way to prevent infection is to avoid mosquito bites.

The control of the infectious agent is based on the reduction of sites that support the reproduction of vectors, such as containers filled with natural and artificial water. This measure requires the mobilization of the entire communities affected. Direct contact with mosquitoes is a significant risk factor for chikungunya, as well as for other diseases transmitted by these insects.

Anyone taking a trip to an area endemic for chikungunya fever runs the potential risk of becoming infected. From this point of view, the categories most at risk, such as pregnant women and those with chronic and immunocompromised diseases, should use the utmost caution. In general, travelers can protect themselves by preventing mosquito bites. Prevention advice is similar to that for other viral diseases transmitted by mosquitoes, such as dengue or West Nile virus. Adopting the following general precautions can therefore reduce any contact with the carrier:

• Use insect repellents on exposed skin. These products should contain DEET (N, N-diethyl-3-methylbenzamide), IR3535 or picaridin. Always follow the instructions on the repellent label and consider that sweat reduces the effect. Pregnant women and children should consult their doctors before using these products, while special attention should be paid to children under the age of 3 months, for which use is not recommended.
• Wear long-sleeved shirts and long trousers, which do not leave uncovered parts of the body, and in any case light-colored, because dark clothes attract mosquitoes. It is important to remember that some mosquitoes carrying the disease are not only active in the evening hours, but also during the day.
• Apply mosquito nets on windows and doors to prevent mosquitoes from entering the rooms where they stay (better if impregnated with repellent substances). Even for those who sleep during the day, especially children, the sick or the elderly, mosquito nets treated with an insecticide offer good protection.
• Aedes mosquitoes live in a wide range of habitats and can reproduce in small stagnant water that is collected, for example, in tires, flower pots, cans, children's pools, exhaust pipes and all other open containers. Preventing the formation of stagnant water is a measure to prevent mosquitoes from proliferating.
• When necessary, it is possible to use chemical products or to fight against the carrier (larvae and adult mosquitoes);
• Finally, it is very important that viremic patients avoid being stung by Aedes mosquitoes , so as not to facilitate the further spread of the Chikungunya virus.