Kyasanur forest disease (KFD) is a tick-borne viral haemorrhagic fever endemic (constant presence of disease) in Karnataka State, India. It is also referred as monkey fever by local people. The virus causing the disease: KFD virus (KFDV) is a member of the genus Flavivirus and family Flaviviridae.
KFDV was first identified in 1957, when an illness occurred in monkeys (the black faced langur and the red faced bonnet monkey) in Kyasanur Forest area of Shimoga district, Karnataka State along with febrile illness and few deaths in humans in neighborhood area (Sagar taluk of Shimoga district).
Initially the disease was limited to three taluks (Sagar, Shikaripur and Sorab) of the Shimoga district of Karnataka. In subsequent years disease spread to Uttar Kannada, Udupi, Mangalore (Dakshina Kannada) and Chikmagalure districts of Karnataka.
During 2012-2013, disease was reported from new districts and new states in India: Chamarajanagar district, Karnataka State; Waynad and Malappuram districts, Kerala State and Nilgiri district, Tamilnadu State.
In 2013, an outbreak of KFD occurred in Bandipur Tiger Reserve Forest, Karnataka. In 2014, Thirthahalli taluk of Shimoga district, Karnataka reported an outbreak. Outbreaks occurred in Pali village of Sattari taluka, and three villages (Mauxi, Zarme and Kopardem) under Community Health Centre (CHC) Valpoi, Northeast Goa in 2015.
Evidences of KFD virus or related viruses were found in different parts of India (parts of the Saurashtra region in Gujarat State, forested regions west of Kolkata, West Bengal State, and the Andaman Islands) during serological studies.
The increase in number of new foci and cases indicates that ecobiological changes due to deforestation and use of new land for farming and cattle grazing could lead to spread of KFD virus to newer geographical areas.
Viruses related to KFDV have been identified in China and Saudi Arabia.
The incubation period of KFD is about 2 to 7 days after tick bites or exposure.
The onset of symptoms is sudden, with chills, frontal headache, severe myalgia followed by fever. The increase in temperature is continuous and lasts for 5-12 days or even longer.
Muscle pains occur at the nape of the neck, lumbar region and calf muscles. Gastrointestinal symptoms as diarrhoea and vomiting may occur at third to fourth day of illness. Patient may feel photophobia (discomfort in the eyes due to light exposure).
In the majority of cases there are no haemorrhagic manifestations but in few cases bleeding from the nose, gums, gastrointestinal haemorrhage (blood in vomit or fresh blood in the stools) and cough with blood tinged sputum/haemoptasis(coughing up blood) may occur.
Physical examination reveals enlargement of cervical lymph nodes and papulovesicular lesions on the soft palate.
Most of the patients recover without any complications after one to two weeks of symptoms. In few patients the disease runs a biphasic course; the second phase starts in the third week of illness after a febrile period of one to two weeks. It is characterized by return of fever and neurological symptoms as headache, neck stiffness, mental disturbance, coarse tremors, giddiness, and abnormality of reflexes.
Case fatality rate is 2% to 10% (% of KFD cases die due to the disease).
KFD is caused by a virus of flavivirus group called KFDV. It is antigenically related to other tick-borne flaviviruses and resembling Russian spring–summer (RSS) complex of viruses.
Mode of transmission of KFD virus:
The virus is transmitted to humans by bite of infected unfed nymphs*(immature stage of tick). Human to human transmission is not known.
Natural hosts and reservoirs- Small mammals particularly rats and squirrels are main reservoir of the virus. Monkeys act as amplifying hosts for the virus and disseminate the infection, but most of them die from KFD infection. Cattle maintain tick population by providing them blood meal but play no part in virus maintenance. Man is incidental or dead end host, and plays no role in viral transmission.
Vectors- Hard Ticks of genus Haemaphysalis transmit the disease. Spinigera species of Haemaphysalis is the main vector of KFD and is commonly found in Karnataka State, India. Humans become infected through the bite of infected unfed nymphs when they pass through the forests. Adult ticks feed on large animals like cattle. These large animals are good hosts for proliferation of ticks but are not significant for virus dissemination due to insignificant viremia (presence of virus in blood) in them. Ticks also transmit this virus transstadially (from one life stage to next) thus also acts as reservoir for the virus.
(*Life cycle of hard ticks- Hard ticks have four developmental forms; egg, larva, nymph and adult (female and male). Adult fed female tick lays eggs on the ground, which hatch to larvae under the vegetations. The larvae further infest and feed on small mammals and monkeys, drop on the ground and change into nymphs. Nymphs feed on small mammals, birds, (as well as accidentally infesting humans), drop on the ground and mature in to adults. Adult ticks usually feed and mate on large animals such as cattle, monkeys. Such type of ticks, feeding on three different hosts is called three-host ticks, one each for the larval, nymphal, and adult life stages).
The disease should be differentiated from other diseases such as influenza, typhoid, dengue, malaria, leptospirosis, rickettsial group of fevers. The following tests should be performed on blood samples:
Diagnosis of KFDV-
There is no specific treatment for KFD.
Management of disease is mainly supportive in the form of maintenance of the hydration and measures to prevent and control bleeding disorders and neurological complications.
Hemorrhagic manifestations, including intermittent epistaxis, haematemesis, melena, and frank blood in the stools.
Neurological complications may occur due to meningoencephalitis. Symptoms include headache, neck stiffness, mental disturbance, coarse tremors, giddiness, and abnormality of reflexes.
Prevention of KFD includes vaccination, personal protection and control of ticks in KFD endemic areas.