WikiJournal Preprints/An overview of Kyasanur Forest Disease
Introduction[edit | edit source]
Kyasanur Forest Disease (KFD) is an emerging, tick-borne, zoonotic disease caused by the pathogenic KFD virus of the family Flaviviridae . Endemic to India, especially the southern districts, it manifests as an acute, febrile, hemorrhagic illness in both humans and monkeys with seasonal outbreaks occurring from January to June each year . The KFD virus (KFDV) is classified as a Biosafety Risk – Group 4 organism as it causes deadly disease in humans with no specific cure or treatment existing for public use . For over sixty years, KFD incidence was only reported in some forest districts in the state of Karnataka until cases began appearing in adjacent states along the Western Ghats region of the country . The spread of KFD out of Karnataka as well as the long-standing seropositivity against KFDV-like viruses in non-adjacent states emphasizes the growing relevance of this tropical disease and the need to address the rising infection rates in humans (?). This review aims to inform both academic and public communities about the epidemiology, virology, pathophysiology and clinical nature of Kyasanur Forest Disease as well as consolidate the most recent data on regions of India at increased risk for KFD infection.
History[edit | edit source]
Human cases of KFD were first reported in the Shimoga district of Karnataka during an outbreak of febrile illness in 1957 . Indications toward an unknown epizootic disease came from numerous reports of local, non-human primate deaths and subsequent reports of severe febrile illness in villagers living in and near the forests where the monkey remains had been found . Veterinary scientists who had been investigating the monkey deaths were bitten by KFD-infected ticks and developed a hemorrhagic illness which helped to identify the origin of the infection . Serological investigations conducted at the Virus Research Center in Pune likened the KFDV to the Russian spring-summer encephalitis (RSSE) group of arboviruses which are typically associated with neurological syndromes. While there was some evidence for neurological disease, further analyses found no definitive sign of encephalitis or meningitis so the following clinical descriptions of KFD emphasized the hemorrhagic features of KFD rather than any neurological abnormalities . After these initial reports, however, the majority of clinical and lab cases did not exhibit such severe hemorrhagic complications . Subsequent studies then focused on the neurological aspects of KFDV infection and suggested similarities to both hemorrhagic and encephalopathic viral illnesses in Europe, Saudi Arabia, Russia, Japan and China based on viral genomic sequences . The general consensus is that KFD has a biphasic presentation, which is sometimes further divided to create four phases overall . According to the biphasic description, the initial phase includes some hemorrhagic symptoms and the latter phase is dominated by neurological manifestations.
Epidemiology[edit | edit source]
Prevalence[edit | edit source]
Since its identification in 1957, the estimated incidence of KFD in India has been 400-500 cases per year with reported infection mortality rates from 2-10% . The number of incident cases was relatively steady until large numbers of human infections were reported in 2003 with marked declines in 2007 and 2010 . In 2012, 69 of 314 reported KFD cases were confirmed with a case fatality rate of 1.4%. Overall, from 2003 to 2012, there were 3 263 reported human cases in India of which 823 were laboratory confirmed with a confirmed case fatality rate of 3.4% .
- Need additional data on more recent prevalence and incidence*
Distribution[edit | edit source]
From 1957-2012, KFD was localized primarily in Shimoga district, Karnataka with disease cases constantly present in that region; although Uttar Kannada, Dakshin Kannada, Chikmagalur and Mangalore districts began reporting KFD cases in that time period as well . The first reported cases of KFD out of those five endemic districts came in 2012-2013 out of the Bandipur Tiger Reserve, Karnataka . Over the next few years, reported and confirmed KFD cases out of Karnataka state rose; Tamil Nadu in 2012, Kerala from 2013-2015, Goa from 2015-2017 and Maharashtra from 2016-2017 . While the cases in Karnataka continued to be reported regularly, incidence in Goa and Maharashtra increased in 2017 and spread to more districts within the two states in those three years – see Figure 1 .
Although not as conclusive as having reported KFD cases, a handful of regions and states outside of those aforementioned have been found to have populations with antibodies against KFDV or a KFDV-like virus . Evidence from surveillance surveys conducted in the 1950s showed that populations in the Kutch district and Saurashtra region in Gujarat and the forested regions west of Kolkata in West Bengal were seropositive for KFDV, or another closely related virus . More recently, seropositivity for KFDV-like viruses had also been found in the human populations of the Andaman and Nicobar islands, although no corroborating data from KFD case reports were available .
Ecology[edit | edit source]
While seropositivity for KFDV and KFDV-like viruses is scattered around the country, the confirmed cases of KFD have been localized to the Western Ghats belt of India that shares common ecological characteristics, making it a high-to-moderate risk region for KFD infection . Most of the belt area consists of thick rainforest populated by deciduous and semi-deciduous trees and shrubs covering hilly land that sees an average of 85 inches of rainfall per year . The humidity and fertility of the soil make it ideal not only for human farming purposes but also for the sustainability of wild monkeys and thereby the maintenance of ticks . The wildlife sanctuaries and forest reserves ensure the maintenance of adequate animal reservoirs for KFDV to circulate and sustain a high-risk environment for the susceptible people who work and live in these forest regions.
A review article by Boshell published in 1969 suggested that significant changes to the local ecosystem and encroachment of humans into the forest were the pretext for the 1956-1957 KFD outbreak. Animal sero-surveillance in the 1950s had shown that a KFDV-like virus had been circulating in this and other regions of India for a few years, only occasionally affecting humans . The lack of documented cases of KFD prior to 1957 suggested that the disease may not have been recognized as new and may have been ascribed to a different cause; as had been done before with KFD monkey deaths assumed to be caused by the plague or an influenza pandemic .
Boshell proposed that human exposure to this inconspicuous virus had increased with deforestation and timber-harvesting practices which necessitated prolonged presence in tick hosts’ habitats . He further supported his reasoning with the fact that, in the 1950s, the human population in that region of Shimoga district had more than doubled – providing more opportunities for transmission and infection. The KFD epidemic periods also correlated well with the periods of greatest human activity in forests; after September (end of monsoon season) from November to December (paddy harvest) and December to May (gathering firewood and other forest products) . People residing in an around these forests are exposed to ticks while farming or grazing/herding their livestock, collecting dried leaves or wood, hunting, hiking and disposing of dead animals .
Cause[edit | edit source]
The isolation and identification of KFDV in 1957 using serum and tissue samples from dying monkeys in Shimoga was the first piece of evidence for the presence of a tick-borne flavivirus with uncertain etiology in India . Following this finding, research shifted focus to identifying the primary vectors and reservoirs of the disease. Haemaphysalis spinigera ticks were the dominant species from which KFDV was isolated but later studies, from 1964-1978, found several other Haemaphysalis species were also competent reservoirs as were other genera of local ticks such as Rhipicephalus, Hyalomma and Ixodes . Small mammals (monkeys, rats, bats, mice and squirrels) and large animals (cattle, goats, buffaloes, wild bears and porcupines) are known to serve as good hosts and have been considered reservoirs for tick-borne flaviviruses, which means they become infected and develop anti-bodies against the virus without becoming ill .
- Virology and genetic information.
- KFDV is a spherical, enveloped virus with a diameter of 45nm. Single-stranded, positive-sense RNA (Pattnaik, 2006); which means it can function as messenger RNA (mRNA) and be translated into proteins by the hosts’ cells. Cytopathic – the virus causes morphological or physiological changes in the host cell leading to its lyses or the cell dies because it couldn’t reproduce.
- Use: Grard et al., 2006 and Dodd et al., 2011 papers*
Transmission[edit | edit source]
KFD is transmitted to humans through tick bites, especially those ticks in the nymphal stage of their life cycle since Jan-May, when human KFD infections occur, is when nymph activity is highest . Ticks feed by creating a feeding pool under their hosts’ skin and ingesting the blood and fluids that flow into it, simultaneously releasing pheromones that attract more ticks from other life-stages to the same pool . Growing evidence has shown that such co-feeding by various tick life-stages on mammalian hosts is the primary means of virus transmission among ticks . After mosquitoes, ticks are the second most competent and versatile vectors of pathogens as they can live for several years in unfavorable environmental conditions, have high reproductive potential and a tendency to feed on a variety of hosts throughout their life stages . Small animal species, like monkeys and rodents, act as ideal hosts because their migration and wandering disperse ticks who take advantage of the constant supply of naïve animals .
Other than ticks, direct transmission from rodents to humans is also possible but there is no evidence to show that KFD can be transmitted from humans to humans . In regards to monkeys, the black-faced langur (Presbytis entellus) and the red-faced bonnet macaques (Macaca adiate) act as sentinel species – animals that are useful to monitor since illness risks to humans can be detected early . KFD outbreaks in monkeys were recorded in two studies spanning 1957-1964 and 1964-1973. While the black-faced langur was more susceptible to KFD than the macaques, the burden of mortality in both species was high in both reported and confirmed KFD cases . Since ticks drop off the body as soon as an animal dies, these monkey carcasses are each hotbeds of KFD infection. The disease process in wild monkeys, especially their deaths during the dry season, correlates well an increase in the Hemaphysalis tick population and the incidence of human cases of KFD .
Pathophysiology[edit | edit source]
Pathogenesis[edit | edit source]
A pathological study in 1963 (n=26) recorded the biochemical and hematological features of KFD patients, finding low white blood cell and eosinophil counts during the first phase of KFD . Another clinical study of hospitalized KFD patients (n=28) found that leucopenia in the acute phase was commonly followed by mild leukocytosis in the second phase with significant drops in red blood cell and platelet counts over the course of illness . In a 1989 review of hemostatic studies, phagocytosis of erythrocytes, white blood cells and platelets were observed following the first phase, with noted evidence of damaged kidney and liver function in the presence of increased bilirubin and gamma globulin levels, reduced serum albumin levels and presence of granular cases, red blood cells and protein in patients’ urine . Findings from earlier post-mortem autopsies of fatal KFD cases were consistent with these studies; with evidence of liver necrosis and tubular damage and renal scarring in the kidneys . Livers, spleens and kidneys were flooded with macrophages and lymphocytes while some cases showed evidence of pulmonary complications like hemorrhagic pneumonia and neurological, aseptic meningitis-like lesions .
Signs and Symptoms[edit | edit source]
KFD, in humans, has a biphasic illness presentation that follows a 2-8 day incubation period after the infected tick bite. The acute febrile period lasts for about 2 weeks, characterized by the sudden onset of fever, chills, headache, diarrhea, vomiting, severe muscle pain and papulo-vesicular lesions on the soft palate in the mouth . Gastrointestinal bleeding, melena (bloody stool), hematemesis (vomiting blood), hemoptysis (coughing up blood), epistaxis (nose bleeds) as well as bleeding from the gums are some of the hemorrhagic features observed during this phase . Inflammations and hemorrhages in the conjunctiva, retina, iris and cornea constitute known ophthalmic symptoms . Other common symptoms include insomnia, hypotension and bradycardia which contribute to the prolonged convalescence of the first phase, taking up to 4 weeks of recovery time .
In 80-90% of cases, patients recover without complications. The remaining 10-20% of patients present with the recurrence of symptoms in the second phase of KFD illness following 1-2 weeks of recovery . This phase is characterized neurological symptoms in addition fever; mental disturbances, stiff neck, confusion, delirium, abnormality of reflexes, tremors, photophobia, and pleocytosis . Although there is a lack of clear evidence for meningitis and encephalitis in KFD patients, symptoms like drowsiness, disorientation convulsions, loss of consciousness and, more rarely, coma, other signs of neurological exacerbation and death have been observed . The case fatality rate for KFD infection is 2-10% whereas recovering patients continue to be lethargic and suffer tremors for several weeks before the symptoms eventually resolve .
Diagnosis[edit | edit source]
- Surveillance to monitor for symptoms, confirm diagnosis with rapid diagnostic methods (RT-PCR, real-time RT-PCR), viral isolation, IgM-capture ELISA, immunofluorescence, haemagglutination inhibition or neutralization tests – descriptions in Mourya et al., 2012, Pattnaik, 2006, Adhikari et al., 1993.
- Use: Chaubal et al., 2018 paper
Treatment and Prognosis[edit | edit source]
No specific cure or anti-viral drug exists to treat KFD, though early hospitalization for supportive treatment based on patients’ clinical symptoms was recommended for improved outcomes . Hydration and circulation can be maintained by transfusion of intravenous fluids for hypotension, the transfusion of colloids of plasma, platelet and other blood products for those with hemorrhagic symptoms, antibiotics for bronchopneumonia and corticosteroids and anti-convulsants for those with neurological symptoms . Analgesics and antipyretics may be used for the less severe manifestations of the disease .
- Prognosis specific data, case mortality data
Prevention[edit | edit source]
Minimizing exposure to ticks is the most effective means of preventing KFD infection. Using insect repellents and protective clothing while working or moving around in the forest areas where ticks are endemic or when handling or being in close proximity to wild rodents and monkeys.
- Describe the history of KFD vaccine development? Expand section using: Holbrook, 2012, and cited paper.
In 1990, the Karnataka state government initiated a vaccination campaign targeting the five districts of the state in which KFD was endemic . Two doses of the formalin-inactivated, tissue culture vaccine were to be taken at baseline and one month with a booster shot 6-9 months later . Due to the low efficacy of the vaccine, 62.4% with first two doses and 82.9% with all three, recommendations were given for booster doses to be administered annually for the next five years .
- Add more info.
Disease Control and Public Health[edit | edit source]
One Health Approach[edit | edit source]
- Required because KFD is a zoonotic disease. Previous literature has advocated for a holistic approach involving professionals and experts from the medical, veterinary and vector-biology fields to ______? .
Surveillance and Risk Mapping[edit | edit source]
The Western Ghats belt is already known to be a high-risk region for KFD infections so surveillance in the area to track monkey deaths and early human KFD cases will help to predict outbreaks and, hopefully, direct immunization efforts and proactive tick-control procedures to increase coverage and prevent infections .
- Insert Figure 3 from Peterson 2017 paper (under creative commons license)
Disease Control[edit | edit source]
- Current approach to put up a 100km border around outreak sites for vaccination of at-risk populations etc.
Additional information[edit | edit source]
Acknowledgements[edit | edit source]
Any people, organisations, or funding sources that you would like to thank.
Competing interests[edit | edit source]
Any conflicts of interest that you would like to declare. Otherwise, a statement that the authors have no competing interest.
Ethics statement[edit | edit source]
An ethics statement, if appropriate, on any animal or human research performed should be included here or in the methods section.
References[edit | edit source]
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