Abstract

The main issue discussed in the paper is Chikungunya arbovirus, which is an acute infectious disease belonging to the group of tropical mosquito fevers. The main research questions include the history of condition; the level of epidemiological conditions since the first outbreaks in Africa till current state in the whole world and ways of prevention. The aim of the current paper is to point out the peculiarities of the Chikungunya fever transmission and means of treatment, analyze the process of epidemiological conditions development and identify the preventive measures to avoid developing the disease. The main methods are data collection and analysis. The papers results identified the vulnerability of people to the diseases transmitted by insects, displayed clinical symptoms of the disease, showed the dynamics of the epidemic proliferation, and indicated the main means of disease prevention. Conclusion summarized the disease condition and epidemiological situation. It also identified the peculiarities of treatment and means of disease prevention.

Chikungunya

Recently, the most widely spread health threats are Zika, Dengue and Chikungunya viruses. These viruses belong to the category of arboviruses - a large group of viruses, classified on the basis of their ability to multiply in the body of bloodsucking arthropods and infect vertebrate hosts. The geographical spread of arboviruses is limited by environmental parameters governing their transmissible cycle. Africa, Asia and South America are the areas of maximum spread of these viruses. One of the typical examples of the so-called newly returned arbovirus is Chikungunya fever caused by a virus with the same name. Chikungunya is a threatening virus the treatment of which is complicated because of the lack of appropriate and effective medicines and vaccines.

History of Condition

Chikungunya virus (CHIKV) is a disease caused by alphavirus with the similar name. Aedes aegypti and Aedes albopictus mosquitoes transmit the virus to people by the blood drawn while stinging. Contamination of a healthy man is carried via saliva of mosquitoes that were infected a few days or weeks earlier.

Chikungunya fever is an alphavirus of the Togaviridae family. The name "Chikungunya" comes from the verb in the kimakonde language meaning "to become contorted", which corresponds to the appearance of hunched people suffering from joint pain.

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A person can get infected with Chikungunya virus through the bite of a female mosquito. The virus is also transmitted from person to person. There is evidence that animals including primates can also become virus carriers. Like the yellow fever it circulates between monkeys and mosquitoes, and in urban areas is transferred from one person to another. The same cycle is established in Asia where Chikungunya has spread rather widely. In rural areas of Africa, the incidence has been sporadic, and in the cities of Africa and Asia the epidemic occurs periodically.

Only females are hematophagous (that is to say, the insect must feed on blood to ensure the development of its ovaries and eggs) and therefore able to transmit Chikungunya. This capability "vector" of the female Aedes reflects an ability to duplicate the virus (not by the amount of fully absorbed blood). Contrary to a popular belief, it is not absorbing the blood, but just before injecting a bit of anesthetic and anticoagulant saliva into a blood vessel of its victim, the mosquito infects the host. Males being herbaceous sap-sucking or fruit nectars are deprived of mouthparts that can pierce skin of vertebrates. A female mosquito becomes infected by biting a human or a contaminated animal. The blood then passes through the stomach in the animal body. The female Aedes is infected after several days of development of the virus in the body until it reaches the salivary glands. It becomes infected for the rest of its life, about one month. However, it stings and ponds every four days. Seven to eight transmissions of the virus by the mosquito are a possible rate of contamination with as many people. An Aedes female lays about 300 eggs in its lifetime.

It is believed that the Chikungunya virus is of African origin. It has two genetic types, one located in West Africa and the other in eastern and southern Africa. It is possible that the mutation of a gene encoding a protein of the viral envelope can change the nature infecting the mosquito vector and partially explain the large spread of virus in the year 2003. The genome of the virus isolated in Reunion was sequenced; it contains 14,500 nucleotides and drifts of the African strain.

Aggressive peak of mosquitos activity is early in the morning and the end of the afternoon. (WHO, 2014) After the amplification of mosquito cells which multiply very quickly in the several tens of millions of viral particles per milliliter of culture supernatant, the virus was analyzed by electron microscopy with the help of a negative staining technique. Its size is 70 nanometers; it is round and one can distinguish its capsid surrounded by an envelope.

There is a vertical transmission, which means that the eggs laid by infected female are contaminated in a very small proportion (1-2%), and therefore there is no real effect on the transmission of the disease. There can also be an in utero transmission of the virus from mother to child (forty cases have been reported in 2005-2006 in Reunion).

Chikungunya virus has certain symptoms, allowing identifying it in time. The disease can usually be diagnosed is 4-8 days after the bite of an infected mosquito. After an incubation period, such symptoms as fever, severe arthralgia, chills, headache, photophobia, conjunctival hyperemia, loss of appetite, nausea and abdominal pain suddenly appear. A migratory polyarthritis mainly affects the small joints of the hands and feet, as well as wrists and ankles. The rash appears from the outset or after 2-3 days while the fever is recessing. The most intense rash is observed in the trunk and extremities. Sometimes there are petechiae and epistaxis, but overall bleeding is uncommon, even for children. Some patients reveal leucopenia (WHO, 2014). The clinical picture is characterized by the increase of Aspartate transaminase activity and concentration of C-reactive protein in blood, as well as slightly reduced platelet count. Recovery can take several weeks. The elderly (especially - in carriers of HLA-B27 antigen) develop stored joint stiffness and arthralgia, which are permanent symptoms, while effusion appears occasionally. Individual cases with disorders of the gastrointestinal tract and neurological, ocular, cardiac complications have also been registered. The serious complications of the disease are rare, but among older people the disease can be fatal. Chikungunya can then lead to serious neurological damage to the fetus, which can cause death in utero during the second quarter (3 cases in Reunion). But the main risk consists in childbirth viremic period, that is to say, the period when the mother is sick with Chikungunya. In half of the cases, the child is infected with the virus and encephalitis, which account for10% of cases. By biting an infected person, the mosquito gets infected with the virus and can transmit it.

Chikungunya fever typically lasts from five to seven days and often causes severe pain in the joints, which sometimes lasts for a long time (WHO, 2014). The detailed clinical picture of infection is more common in adults. Chikungunya fever rarely takes a life-threatening form. However, there is no special treatment of Chikungunya fever at present, but to relieve pain and swelling one can use painkillers and non-steroidal anti-inflammatory drugs. One should not take aspirin. The treatment of people infected by the virus Chikungunya fever is carried out exclusively in hospitals.

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One can become infected with Chikungunya only once. After injecting antibodies that are responsible for protecting the sick, the patient is supposed to develop immunity for life according to the available evidence.

Epidemiological Conditions

Chikungunya viral disease transmitted by mosquitoes was first described during an outbreak of the disease in Southern Tanzania in 1952 (WHO, 2014). Chikungunya is prevalent in Asia, Africa, and the Indian subcontinent. Over the years, the level of infection in Africa remained relatively low. In 1999, there was a Chikungunya epidemic in the DRC with 50,000 infected. In the years 2001-2003, the Indonesian island of Java was hit by an epidemic.

In February 2005, a major outbreak of the disease occurred on the islands of the Indian Ocean (WHO, 2015). In 2006, the epidemic on the islands of the Indian Ocean has reached its peak and caused a large number of imported cases in Europe. More than 1.25 million people in India and South Asia have been infected from February to October 2006. Other large-scale outbreaks of the disease occurred in the Eastern and Central Africa and the Indian Ocean islands, including Comoros, Gabon, Maldives, Mauritius, Madagascar, Mayotte, Reunion Island (France), Seychelles and South-East Asian countries (CDC, 2015a).

Until 2006, Chikungunya viral disease infected American tourists rarely. From 2006 to 2013, the annual average rate in the United States with a positive test for the recent Chikungunya virus was 28 people. The rate reached 5-65 people within a year. They were all travelers who visited infected areas in Asia, Africa or the Indian Ocean and returned to the United States (CDC, 2015a).

In 2007, the first European outbreak was recorded in north-eastern Italy. In September 2007, as a result of imported cases, Chikungunya outbreak was registered in the northern part of Italy. The extension of Chikungunya through the boundaries in recent years represents people vulnerability to infectious diseases transmitted by insects. It emphasizes the importance of implementing sustainable programs to address them as an integral component of security in the field of healthcare.

Before 2013, Chikungunya virus was identified in Africa, Asia, Europe and the Indian and Pacific Oceans (WHO, 2015). At the end of 2013, in the Caribbean area, there was identified the first local transmission of Chikungunya virus in the United States. Local transmission means that people are infected by bites of mosquitoes locally.

Since then, more than 1.7 million suspected cases were identified in 45 states and territories across the US due to the local transmissions (CDC, 2015a). Starting from 2014, the cases of Chikungunya virus have been identified among US travelers who came back from the affected areas in North and South America, while Florida, Puerto Rico, and US Virgin Islands became places where and the local transmission has been identified.

In 2015, a viral disease became a nationally notifiable condition (CDC, 2016). As of January 12, 2016, 679 Americans have been infected with Chikungunya in total with the outbreak of the disease in 2015. All of the cases have occurred to the travelers who have come back to their homeland from the infected areas. There were no locally transmitted cases in the US (CDC, 2016).

There were registered 202 Chikungunya virus cases in 2015 on the US territory. All of them were locally transmitted from the Virgin Islands and Puerto Rico (CDC, 2016).

In February 2016, there were continuing outbreaks of the disease, especially in Southern countries of the American continent. In February, 12 there were registered 232 confirmed and 14,5 thousand suspected autochthonous transmission cases, mainly in Mexico, Nicaragua and in Andean Area (CDC, 2016).

Preventive Measures

There were developed special recommendations for Chikungunya prevention, which correspond to Healthy People 2020 goals in terms of preventing diseases, disabilities, injuries, and premature death.

Avoiding mosquito bites which can happen mainly during the daytime and eliminating mosquito breeding sites are the main ways to avoid Chikungunya fever. One should wear clothing that covers as much skin as possible, and to use repellent on skin and clothes according to the instructions. CDC argues that it is important not to spray repellent on the skin under clothing. Repellents containing DEET, IR3535, picaridin, para-menthane-diol products, and oil of lemon eucalyptus provide long lasting protection (CDC, 2015b).

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One on the main goals of Healthy People 2020 is to promote enhanced quality of life, healthy development, and healthy behaviors across people of all age groups (CDC, 2011). WHO is developing outbreaks management plans on the basis of the given evidence. It also provides technical support and guidance for effective outbreaks management and control, including reporting systems improvement. WHO also provides specific trainings in clinical management, diagnosis and vector control at the regional level. It encourages the creation and maintenance of the ability to identify and confirm cases of the disease, patient management, and implementation of social policy information to reduce the presence of mosquitoes (WHO, 2015).

To minimize the risk of Chikungunya development, CDC recommends to empty standing water from flowerpots or buckets, drinking bowls for pets, as well as the abandoned car tires and food containers or other containers near residential homes and workplaces, such as water storage (CDC, 2015b). The use of air conditioning or window/door screens and mosquito bed nets also minimize a risk of mosquito bites among children, the elderly and sick people, as well as those who prefer resting in the daytime.

American scientists have developed a vaccine against the Chikungunya fever but it has not yet passed the testing. The study was conducted by a group of experts of the National Institute of Allergy and Infectious Diseases of the USA. The staff of the Vaccine Research Center at NIAID discovered several Chikungunya virus structural proteins, on which base virus-like particles was created in the laboratory. These particles are structurally similar to the causative agent of fever, but can not cause infection. Virus-like particles were given as an injection to rhesus monkeys and 15 days later the scientists infected animals with Chikungunya virus. It was found that injection of these particles helped produce antibodies. They provided animals with complete protection against the infection (NIH, 2014). In the next phase of the study, immunosuppressed mice were injected with antibodies serum obtained from monkeys. After that rodents have been given a lethal dose of Chikungunya virus. However, the introduction of serum prevented the development of fever. The director of the Vaccine Research Center Gary Nebel said that his colleagues intended to obtain permission for clinical trials to develop a vaccine. In addition, the researchers believe that the method of virus-like particles will be applied for the development of vaccines against diseases caused by other alphaviruses, such as Western and Eastern equine encephalitis and fever o'nyong'nyong virus.

Conclusion

Chikungunya is a tropical viral disease that occurs mostly in South Asia and East Africa and is transmitted by mosquitoes. Analysis of modern epidemiological conditions show that focus of infection of the American continent is mainly located is southern countries. Nowadays, there is no specific treatment, but there are some medications which can help to reduce the symptoms. There is no antiviral vaccine against Chikungunya virus, i.e., there is still no cure for it. The best prevention is the general mosquito control and also avoidance of the possibility of being bitten by infected mosquitoes.

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