Synonym
Type of zoonosis
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Metazoonosis type IV
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Vector-borne zoonosis
Definition
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Kyasanur forest disease (KFD) is a tick-borne viral haemorrhagic fever, caused by Kyasanur forest disease virus, transmitted by bite of an infected tick nymphs (Haemaphysalis spinigera). KFD is named after its location, Kyasanur forest area in Soraba and Sagar talukas of Shimoga district of Karnataka in India. KFD is clinically characterized by sudden onset with fever, cephalalgia, myalgia, anorexia, insomnia and prostration, bradycardia and hypotension, and less frequently coughing and abdominal pain.
Brief history
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In 1957, several dead monkeys were noticed in the Kyasanur forest in Soraba and Sagar taluks of Shimoga district in Karnataka along with a severe prostrating illness in some of the villagers in the area. A similar illness has been observed in the locality a year earlier also. A new antigenically related to the Russian spring-summer encephalitis complex of viruses was isolated by investigators from patients and dead monkeys. It was named as the KFD virus after the name of the place from where the first isolations were made.
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The infected area in the Kyasanur forest has increased since 1957 from 800 sq.km to 4000 sq.km.
Etiology
Reservoir and incidence
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KFD is limited to Karnataka state, India. Though human infection is usually found in certain areas in Karnataka, the virus appears to be more widespread in distribution as evidenced by KFD antibody in man and animals in the Kutch and Saurashtra Peninsula and sporadically from other parts of India. Recently, a virus very similar to KFD virus known as Alkhurma. Haemorrhagic Fever virus (AHFV) was discovered in Saudi Arabia. KFDV and AHFV share 89% sequence homology.
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People with recreational or occupational exposure to rural or outdoor settings (eg: Hunters, campers, forest workers, farmers) are potentially at risk for infection.
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Outbreaks of KFD in human beings residing by the side of the forest occur generally in dry months (summer season - January to June) when field workers go to forests more frequently. This period is also coinciding with increased tick activity. Human being visiting natural nidus of infection may be bitten by infected ticks. Alternatively, cattle grazing in the forest bring on to the human inhabitants, then the infected ticks crawl down to reach human beings to bite.
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Deforestation changed the uniform conditions of the environment and results in evergreen forest vegetation changed to deciduous vegetation. This change has favoured the proliferation of the tick H.spinigera.
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Porcupines, rat, mice, forest birds and small mammals act as reservoir hosts. KFDV.
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Haemaphysalis ticks acts as reservoir to some extent, in which transovarian transmission of the virus has been demonstrated.
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Monkeys act as amplifier host.
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Man and cattle are accidental hosts.
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There is no evidence of the disease being transmitted via unpasteurized milk of these animals.
Transmission
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By contact with an infected animal, such as sick/recently dead monkey.
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By bite of an infected tick nymphs (Haemaphysalis spinigera).
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The adult Heamaphysalis spinigera ticks feed on large wild or domestic animals, and then fell down on the ground. The larvae and nymph attach themselves to humans, various small mammals of the forest, as well as birds and monkeys and transmit the virus.
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The virus has also been isolated from H.turturis, in the nymphs of which the agent can survive throughout the year, and from six other species of Haemaphysalis, several species of lxodes, and the tick family Argasidae.
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The introduction of cattle in the jungle has facilitated the spread and increased density of H.spinigera, along with higher circulation of the virus.
Disease in monkeys
Disease in man
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The incubation period ranges from 3 to 8 days.
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KFD has sudden onset with fever, cephalalgia, myalgia, anorexia and insomnia. On the third or fourth day, the patient tends to experience diarrhoea and vomiting.
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Severe prostration, papulovesicular lesions on the palate are a consistent finding.
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Bradycardia and hypotension are prominent signs.
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Less frequently symptoms of coughing and abdominal pain.
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The fever lasts for 6 to 11 days. After a febrile period of 9 to 21 days, a significant proportion of the patients undergo a second phase of pyrexia that lasts for 2 to 12 days, usually with neurologic symptoms such as stiffness of the neck, mental confusion, tremors and abnormal reflexes.
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Palpable cervical and axiliary lymph nodes.
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Haemorrhagic manifestations in agricultural workers who are poor and malnourished.
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Leukopenia is common.
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Convalescence is prolonged. A small proportion of patients develop coma or bronchopneumonia prior to death.
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The case fatality rate is approximately 5% to 10%.
Diagnosis
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Blood and paired sera should be collected.
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Serologic diagnosis by complement fixation, haemagglutination inhibition, neutralization tests and ELISA using paired sera.
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Serologic diagnosis is more difficult if the patient has been previously exposed to another Flavivirus.
Treatment
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Supportive therapy and clinical management are important, include maintenance of hydration and prevention of bleeding disorders.
Prevention and control
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Individual human protection against ticks is very much important, such as protective clothing and the use of repellents.
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A formalin-inactivated chick embryo fibroblast tissue culture vaccine produced, but, demonstrated only 59% seroconversion in a field trial in the endemic area. The presence of antibodies to other Flaviviruses, especially the West Nile virus, seems to interfere with the vaccine’s efficacy.
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In mice, it is reported that 70 to 100% protection against large doses of KFD virus for at least 18 months with single inoculation of a live vaccine based on an attenuated strain of Langat virus.
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Tick control measures to be followed in KFD prevalent areas.
Tick control
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To remove attached ticks, use the following procedure
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Use fine-tipped tweezers or shield your fingers with a tissue, paper towel or rubber gloves.
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When possible, persons should avoid removing ticks with bare hands.
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Grasp the tick as close to the skin surface as possible and pull upward with steady, even pressure. Do not twist or jerk the tick; this may cause the mouth-parts to break off and remain in the skin (If this happens, remove mouth-parts with tweezers. Consult your health care provider if infection occurs).
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Do not squeeze, crush or puncture the body of the tick because its fluids (saliva, body fluids, gut contents) may contain infectious organisms.
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After removing the tick, thoroughly disinfect the bite site and wash your hands with soap and water.
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Save the tick for identification in case you become ill. This may help your doctor make an accurate diagnosis.
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Note the date of the bite and place the tick in a plastic bag and put it in your freezer.
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Avoid use of petroleum jelly or hot matches for tick removal. They may make matters worse by irritating the tick and stimulating it to release additional saliva or regurgitate gut contents, increasing the chances of transmitting the pathogen.
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To avoid tick bites and infection, follow these tips
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Avoid tick infested areas, especially during the warmer months.
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Wear light coloured clothing so ticks can be easily seen.
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Wear a long sleeved shirt, hat, long pants and tuck pant legs into socks.
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Walk in the centre of trails to avoid overhanging grass and brush.
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Check your body every few hours for ticks when you spend a lot of time outdoors in tick infested areas. Ticks are most often found on the thigh, arms, underarms and legs. Ticks can be very small (no bigger than a pinhead).
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Use insect repellents containing DEET (n,n diethyl m.toluamide), DDT (Dichloro Diphenyl Trichloro Ethane), HCH on your skin or permethrin on cloting. Be sure to follow the directions on the container and wash off repellents when going indoors.
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Remove attached ticks immediately.
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