Chikungunya Virus: Etiology & Clinical Features

We kick Off our Back to College series Article on Chikungunya with our first article on Chikungunya Virus: Etiology & Clinical Features

Introduction

Chikungunya fever (CF) is a viral illness caused by an arbovirus transmitted by the Aedes mosquitoes. The disease was documented first time in the form of an outbreak in Tanzania. The name is derived from the ‘makonde’ dialect which means ‘that which bends up’, indicating the physical appearance of a patient with severe clinical features.

Causative Agent

Chikungunya fever is caused by virus of same name (CHIK virus in short) which is an RNA virus that belongs to the Alphavirus genus of the Togaviridae, the family that comprises a number of viruses that are mostly transmitted by arthropods. The virus was first isolated in 1952-1953 from both man and mosquitoes during an epidemic of fever that was considered clinically indistinguishable from dengue fever in Tanzania.

It is a single stranded RNA virus, heat labile and sensitive to temperatures above 580 Celsius. Three lineages with distinct genotypic and antigenic characteristics have been identified: two phyllogenetic-groups from Africa and one from Asia. Chikungunya virus strains isolated in India during the 2006 outbreak are closely related to strains isolated that year from Réunion islands.

Vector

Aedes aegypti is the common vector responsible for transmission in urban areas whereas Aedes albopictus has been implicated in rural areas. Recent studies indicate that the virus has mutated enabling it to be transmitted by Aedes albopictus.

The Aedes mosquito breeds in domestic settings such as flower vases, water-storage containers, air coolers, etc. and peri-domestic areas such as construction sites, coconut shells, discarded household junk items (tyres, plastic and metal cans, etc.). The adult female mosquito rests in cool and shady place.

Epidemiology

In the South-East Asia Region, Chikungunya virus is maintained in the human population by a human-mosquito-human transmission cycle that differs from the sylvatic transmission cycle described on the African continent. A high vector density as seen in the post monsoon season accentuates the transmission.

Chikungunya fever epidemics display cyclical and seasonal trends. There is an inter-epidemic period of 4-8 years (sometimes as long as 20 years). Outbreaks are most likely to occur in post-monsoon period when the vector density is very high. Human beings serve as the Chikungunya virus reservoir during epidemic periods. During inter-epidemic periods, a number of vertebrates have been implicated as reservoirs. These include monkeys, rodents, birds, and other vertebrates.

However, the exact nature of the reservoir status in South-East Asia Region has not been documented. After an extensive outbreak during the beginning of current millennium in the French territory of Reunion Islands in the Indian Ocean, the disease has been reported from almost 40 countries from various WHO regions including South-East Asia.

Moreover, the spread of the disease in South India from 2004 has affected millions of people and left many with crippling disabilities. The disease continues to cause epidemics in many countries.

Clinical  Features

CHIK virus causes a febrile illness in the majority of people with an incubation period of 2-4 days from the mosquito bite. Viremia persists for upto 5 days from the clinical onset. Incubation period can be 2- 12 days.

Fever and Arthralgia are the hallmark of Chikungunya Fever.

Commonest presenting features  are:

  • Fever (92%) usually associated with
  • Arthralgia (87%),
  • Backache (67%) and
  • Headache (62%).

The fever varies from low grade to high grade, lasting for 24 to 48 hours. Additionally, fever rises abruptly in some, reaching 39 to 40 Degrees Celcius, with shaking chills and rigors and usually subsides with use of antipyretics.

No diurnal variation was observed for the fever.

Recent Outbreaks

In the recent outbreaks many patients presented with arthralgia without fever. The joint pain tends to be worse in the morning, relieved by mild exercise and exacerbated by aggressive movements. Moreover, the pain may remit for 2-3 days and then reappear in a saddle back pattern. Additionally, Migratory polyarthritis with effusions may be seen in around 70% cases, but resolves in the majority. Ankles, wrists and small joints of the hand were the worst affected.

Larger joints like knee  and shoulder and spine were also involved. There is a tendency for early and more significant involvement of joints with some trauma or degeneration. Furthermore, Occupations with predominant overuse of smaller joints predisposed those areas to be affected more. (ex: Interphalangeal joints in rubber tappers, ankle joints in those standing and walking for a long time eg. policemen).

The classical bending phenomenon was probably due to the lower limb and back involvement which forced the patient to stoop down and bend forward. Additionally, Clinical presentation of Chikungunya is divided in to three phases.

In Chikungunya mostly symptoms have an abrupt onset with high grade fever, single or multiple joint pains, skin rashes, headache and myalgia.

Clinical presentation of Chikungunya usually follows 3 phases which are as follows:

  1. Acute phase : Less than 3 weeks
  2. Sub-acute phase : > 3 weeks to 3 months
  3. Chronic phase : > 3 months

Clinical presentation may be mild, moderate or severe and most of the symptoms subside within 3 weeks from the onset of symptoms. Moreover, A few of the symptoms may persist for 3 months and even more. Usually 10 – 15 % of the patient those who present with severe Chikungunya progress to Sub-acute or chronic phase.

Other Clinical Features

Mucocutaneous Manifestation

Transient maculopapular rash is seen in up to 50 % patients. The maculopapular eruption persisted for more than 2 days in approx. 10% cases. Moreover, Intertriginous aphthous-like ulcers and vesiculbullous eruptions were noticed in some.

A few persons had angiomatous lesions and fewer had purpuras. Stomatitis was observed in 25% and oral ulcers in 15% of patients. Moreover, the Nasal blotchy erythema followed by photosensitive,hyperpigmentation (20%) was observed more commonly in the recent epidemic.

Exfoliative dermatitis (Hyperpigmentation in Chikungunya Fever) affecting limbs and face was seen in around 5% cases. Additionally, Epidermolysis bullosa was an observation in children. Most skin lesions recovered completely except in cases where the photosensitive hyperpigmentation persisted.

Ocular Manifestation

Photophobia and retro-orbital pain have been observed. Moreover, Neuroretinitis and uveitis in one or both eyes have also been observed.

The main ocular manifestation associated with the recent epidemic outbreak of chikungunya virus infection in South India included granulomatous and nongranulomatous anterior uveitis, optic neuritis, retrobulbar neuritis, and dendritic lesions. Furthermore, the visual prognosis generally was good, with most patients recovering good vision.

(Chikungunya virus uveitis during fever)

Neurologic Manifestations

Reports about encephalitis, febrile seizures, meningeal syndrome and acute encephalopathy were seen.

Moreover, although rare in adults, children, particularly neonates have developed vomiting and/or diarrhoea and meninge-encephalitis.

Gullain – barre syndrome, cerebellar syndrome, neuropathy have also been reported.

Sequelae

Persistent arthralgic forms had been described in 1980 in South Africa. Furthermore, a retrospective study in South Africa had shown complete resolution in 87.9% of the cases. Moreover, among these 3.7% had episodic stiffness and pain, 2.8% had persistent stiffness without pain and 5.6% had persistent painful restriction of joint movements.

Enthesopathy and tendinitis of tendoachilles were observed in upto 53% of those who had musculoskeletal involvement. Additionally, Neurological, emotional and dermatologic sequelae were described.

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Reference:

World Health Organization: Chikungunya in South-East Asia-Update, New Delhi: Regional Office for South-East Asia, 2008. Outbreak and spread of Chikungunya. Weekly Epidemiological Record. 2007 Nov 23; 82(47): 409-415.