Kyasanur Forest Disease virus
المؤلف:
Baijayantimala Mishra
المصدر:
Textbook of Medical Virology
الجزء والصفحة:
2nd Edition , p247-249
2025-12-02
19
Kyasanur Forest Disease (KFD) is a tick-borne viral disease first identified in 1957 when an outbreak occurred in monkeys in Kyasanur forest of Shimoga district in Karnataka, India which was followed by outbreak of hemorrhagic fever in humans of that locality. The causative agent was found to be a virus that was named Kyasanur forest disease virus (KFDV). Virus was first isolated during 1957 outbreak. The disease was mostly restricted to five districts of Karnataka for a long time, and has started showing evidence of spread to other areas affecting more number of cases.
VIRUS
The agent KFD virus is a member of Flaviviridae family, genus Flavivirus and tick born virus group which was previously known as tick-borne encephalitis (TBE) serocomplex and Russian spring summer encephalitis complex. The members of TBE group are associated with neurological manifestations, whereas KFDV is mostly associated with hemorrhagic fever more than neurological symptoms.
TRANSMISSION CYCLE
Kyasanur forest disease virus is maintained in tick-mammal and bird cycle. The virus has been isolated from several species of ticks of which Haemaphysalis spinigera is considered to be the main vector. KFDV is maintained in ticks by transstadial transmission (virus passes through different developmental stages of the tick), and transovarial transmission.
In enzootic state, KFD virus is transmitted between small mammals and ticks. Rodents, shrews and ground birds act as the reservoir of the virus. These animals when infected develop low but sufficient level of viremia to infect the vector, without becoming ill due to infection. Rodents are ideal reservoir due to their short generation time.
Monkeys acquire the infection by bite of infected ticks. Infected monkeys develop high viremia level and thus facilitate the spread of infection. Black-faced langur and red-faced bonnet monkeys are the common species suffered from KFD. Infection in these monkeys can lead to serious illness and deaths commonly known as monkey fever or monkey fall, the two indicators of KFD activity.
The disease in monkeys occurs during dry months of December to May that coincides with increase in nymph population which are highly anthropophilic. Humans, who go to forest for collecting woods or grass or for any other reasons, are at high-risk of acquiring the infection by bite of nymphs. Humans are the dead end host (Fig. 1).
Fig1. Transmission cycle of Kyasanur forest disease
Geographic distribution: KFD is mostly restricted to five districts (Shimoga, Chikmagalore, Uttar Kannada, Dakshin Kannada and Udupi) of Karnataka state in India. Serological evidences have been found in Gujarat, West Bengal and Andaman Island. Since 2011, human cases have been reported from Chamrajnagara and Tirthahalli districts in Karnataka, Nilgiri district in Tamil Nadu, Wayanad and Malappuram districts in Kerala and Palli in Goa. Variants of KFDV have been found from Saudi Arabia and China which were found to have the common ancestor with the Indian isolates.
The number of KFD cases each year varies from 40 to 1000 with an average of 400–500 cases. The mortality rate ranges from 4 to 15% in humans. The disease pattern has showed rising pattern in number of cases during 2003 2004 and again during 2012–2013 with a decline in between.
CLINICAL FEATURES
Incubation period generally ranges from 2 to 8 days. Symptoms start with sudden onset of fever, headache, myalgia and hypotension. The prodromal stage is followed by the stage of complication that is characterized by hemorrhagic manifestations such as petechial hemorrhage on the mucous membrane, bleeding from nose and gum, conjunctival suffusion, hematemesis. In majority of the cases, the symptoms last for 7–14 days, however, in some of the cases a second phase of illness is observed with neurological manifestations like headache, tremor, photophobia and weakness.
LAB DIAGNOSIS
In an outbreak situation, detection of KFD virus can be done from human sample, dead monkey’s tissue and from the tick pools. To confirm the disease in humans, blood samples are collected. Detection of viral RNA by RT-PCR and specific IgM antibody by MAC ELISA are commonly used for confirmation.
Isolation of KFD virus can be done by intracerebral inoculation in suckling mice or in Vero E6 cell line. IgM ELISA and RT-PCR have been developed by National Institute of Virology, Pune, India for diagnosis of KFD. In the past, the outbreaks were confirmed by virus isolation in mice system and demonstration of fourfold rise or fall antibody titer by conventional viral serological tests such as complement fixation test (CFT), hemagglutination inhibition (HAI) test or neutralization.
VACCINE
The first KFD vaccine was prepared in early 1960s which was a mice brain derived formalin inactivated vaccine using RSSE virus which belongs to the same antigenic group as that of KFD. However, it was found not to be protective against KFD, hence not in use.
Presently a formalin inactivated chick embryo fibroblast vaccine has been licensed in India. The vaccine was found to be seroconverted in 70% individuals. In a field trial in 61,000 people who received two doses, it was found to be safe and protective. Amongst the vaccinated individuals, 24 contracted KFD as compared to 325 in unvaccinated population.
The current vaccination strategy is to give two doses of vaccine, subcutaneously, at 4 weeks interval and a booster after 6–9 months of the primary vaccination. Considering the occurrence of cases during the months of December to March, it is recommended to give the first two doses and one booster dose by November month of the year.
الاكثر قراءة في الفايروسات
اخر الاخبار
اخبار العتبة العباسية المقدسة
