Abstract
After having dominated Africa, Chikungunya fever is making headlines in many Asian countries, posing a prominent health problem to an already overstretched health system. The disease is endemic in rural Africa and intermittent epidemics take place in towns and cities of Africa and Asia. India is witnessing surge of this disease which has a significant morbidity.
This paper discusses in brief this disease so as to highlight its important features.
Chikungunya is one more reason, in addition to Dengue and Yellow fever, that A. aegypti must be controlled.

The Chikungunya fever is one of special importance especially in the monsoon season since the atmospheric conditions are favourable for the onset and the propagation of an epidemic. This is of prime concern especially in a metropolis since the crowded conditions may blow up an epidemic to gargantuan proportions. This paper aims to highlight the epidemiology, clinical features and the management of Chikungunya fever especially from the point of view of a medical practitioner who has not specialized in infectious diseases.

Epidemiology

In urban settings, outbreaks of Chikungunya may be explosive. In endemic areas, Sero-prevalence rate may be as high as 90% suggesting that time required for loss of herd immunity is the reason for prolonged absence of cases in a region after an outbreak.¹

Chikungunya virus (CHIKV) is a mosquito-transmitted alphavirus belonging to family Togaviridae.^2,3 It was isolated for the first time from the blood of a febrile patient during the Tanzanian outbreak in 1952.⁴

CHIKV is an enveloped, positive-strand RNA virus. To date, two CHIKV complete nucleotide sequences have been determined, for the strains Ross and S27,⁵ isolated from patients during the 1952 Tanzania outbreak. Another complete nucleotide sequence has been determined for a strain isolated in A. furcifer during the Senegal 1983 outbreak (accession no AY726732). Khan et al5 showed that the S27 genome was similar in its structure to that of other alphaviruses and that O’nyong-nyong virus (ONN) was the closest relative to CHIKV.

CHIKV is geographically distributed in Africa, India and South-East Asia.

In Africa, the virus is maintained through a sylvatic transmission cycle between wild primates and mosquitoes such as Aedes luteocephalus, A. furcifer, or A. taylori.⁶

During outbreaks humans are major reservoirs.

In Asia, CHIKV is transmitted from human to human by Aedes species and other mosquitoes, mainly by A. aegypti and, to a lesser extent, by A. albopictus through an lesser extent, by A. albopictus through an urban transmission cycle.⁶

A. aegypti is a domiciliary mosquito that breeds on abandoned tyres, jars, cans, water storage containers, roof attachments and drains in and around houses. A. aegypti can be easily identified. It has white thoracic scales and black legs with white bands.⁸

Although there have been historic epidemics of chikungunya, particularly in Africa, it is the recent epidemics in Asia that certainly are cause for alarm. Since late 2004 there has been an enormous outbreak in the countries bordering the Indian Ocean. The numbers of cases have been staggering.

There have been reports of large scale outbreak of this virus in Southern India.⁷

An outbreak of Chikungunya fever was reported from Malegaon town in Nasik district, Maharashtra state. In Orissa state, cases of fever with muscle aches and headache were reported recently.⁸ So also in the neighbouring state of Andhra Pradesh.

Pathology

Intensive viraemia occurs within 48 hours of the mosquito bite and wanes 2-3 days later. Onset of haemagglutination inhibition and neutralizing antibodies clear the viraemia. Virus adheres to the platelets causing aggregation. Synovitis probably results from direct viral infection of the synovium.¹

Clinical features of Chikungunya fever

The word Chikungunya is taken from a Swahili word which means “that which bends up” probably referring to the contortions due to joint pains in a patient of Chikungunya fever. The full blown disease is most common among adults. The incubation period is 2-3 days. The cardinal features are fever and severe arthralgia which are accompanied by chills and constitutional symptoms such as headache, myalgia, photophobia, conjunctival injection, anorexia, nausea and abdominal pain.⁹

Facial flushing is common in initial stages.¹
Fever rises abruptly often reaching 39-40 degrees C and accompanied by intermittent shaking chills. This acute phase lasts for 2-3 days. The fever may remit for 1-2 days resulting in a “Saddle-Back” curve.¹⁰

The arthritis is of the migratory polyarthritic type which mainly involves the small joints of the hands, wrists, ankles and feet with lesser involvement of the larger joints. Rash may occur at the onset or at several days into the illness and its appearance may often coincide with defervescence which takes place around day 2 or day 3 of the illness. The rash is most intense on the trunk and the limbs and may frequently desquamate.⁹

Previously injured joints are more severely affected. Large effusions are uncommon. Approximately 10% of the patients have joint symptoms 1 year after infection.
Destructive arthropathy is rare and may be associated with low titer RA factors, suggesting unrelated, underlying inflammatory arthritis.¹

Isolated petechiae and mucosal bleeding may occur but significant haemorrhage is rare.1 Dermatological manifestations (data on file) observed in a recent outbreak of Chikungunya fever in Southern India are as follows.¹¹

Maculopapular rash, Nasal blotchy erythema, Freckle-like pigmentation over centro-facial area, Flagellate pigmentation on face and extremities, Lichenoid eruption and hyperpigmentation in photodistributed areas, Multiple aphthous-like ulcers over scrotum, crural areas and axilla, Lympoedema in acral distribution (bilateral/unilateral), Multiple ecchymotic spots (Children), Vesiculobullous lesions (infants), Subungual haemorrhage. Recovery may necessitate weeks.

Some older patients continue to suffer from stiffness, joint pains and recurrent effusions for several years; which is especially common in HLA-B27 patients.⁹

Diagnosis
Chikungunya should be suspected on the basis of the characteristic triad of fever, rash and rheumatic manifestations.¹⁰

Laboratory investigations

A few patients may develop leucopenia.⁹ Elevated levels of Aspartate aminotransferase (AST) and mildly decreased platelet counts have been described.⁹ A serological test for Chikungunya is available from the University of Malaya in Kuala Lumpur Malaysia. This test involves the detection of virus specific antibodies by capture ELISA in patients recovering from CHIK infection and they persist in excess of 6 months. Haemagglutination Inhibition antibodies appear with cessation of viraemia. All patients will be positive by day 5-7 of illness. Neutralisation antibodies parallel HI antibodies.¹⁰

It must be differentiated from Dengue fever. Virus can be isolated from blood during initial 2-4 days of illness. Complement fixation antibodies are present by third week and reduce slowly over subsequent year. RT-PCR offers an approach to diagnosis more rapidly than viral culture and antibody testing.¹

In case of arthritis synovial fluid shows reduced viscosity and poor mucin clot and 2000-5000 WBCs per cubic millimeter.¹

Management

Supportive care with rest is indicated during the acute joint symptoms.

No specific drug treatment against chikungunya virus is available; thus, treatment of chikungunya fever is supportive: bed rest, fluids, and mild pain medications such as ibuprofen, naproxen, acetaminophen, or paracetamol may relieve symptoms of fever and aching, provided that the person has no contra-indications to these medications.

Movement and mild exercise tend to improve stiffness and morning arthralgia, Because aspirin can increase the risk of bleeding and possibly Reye Syndrome, it should be avoided during the acute stages of the illness. Few cases are severe enough to warrant hospitalization. All persons with chikungunya fever should be protected against additional mosquito bites to reduce the risk of further transmission of the virus.¹²

In unresolved arthritis refractory to aspirin and nonsteroidal antiinflammatory drugs, chloroquine phosphate (250 mg/day) has given promising results in some cases in Kuala Lampur, Malaysia.¹⁰

But use of chloroquine is not FDA approved.

Preventive measures¹²
There are no preventive medications or FDA-approved vaccines for chikungunya fever, but there are steps travellers can take to reduce their risk of being bitten by infected mosquitoes.

• Use insect repellent on exposed skin surfaces when outdoors, particularly during the day.
  1. Repellents containing 30% to 50% DEET (N, N-diethyl-m-toluamide) are recommended. Lower concentrations of DEET offer shorter-term protection requiring more frequent application.
  2. Clothing may also be sprayed with repellent containing permethrin or another EPA-registered repellent for greater protection.
• Wear long-sleeved shirts and long pants when outdoors.
• Stay in hotels or resorts that are well screened or air-conditioned and that take measures to reduce the mosquito population, where possible.
• Reduce Aedes breeding sites by emptying standing water that may have collected in containers (e.g., uncovered barrels, flower vases, or cisterns) and either overturning the vessels or covering the opening.
• If illness develops, stay under a mosquito net or indoors to limit mosquito bites and to avoid further spread of infection.

*Intern, Topiwala National Medical College and Bai Yamunabai Laxman Nair Hospital, Mumbai - 400 008; **Consultant Physician, Asian Heart Hospital, BK Complex, Mumbai.