Promising Experimental Vaccine for Tick-borne Kyasanur Forest Disease Virus
With pathogen-carrying ticks expanding their territories in many parts of the world, a NIAID research group has likewise expanded its vaccine research to two typically rare pathogens with potential for public health importance. The results appear promising.
Few people have heard of Kyasanur Forest disease (KFD) or Alkhurma hemorrhagic fever (AHF), but the closely related viral diseases are, respectively, on the minds of people in India and Saudi Arabia. Both are flaviviruses, part of the same family as Yellow Fever and Dengue.
KFD is mainly spread by Hemaphysalis hard ticks. AHF virus, which is a variant of KFD virus, is spread by hard ticks (Hyalomma dromedary) and soft ticks (Ornithodoros savignyi). Both viruses are hemorrhagic fever viruses, meaning they can cause internal and external bleeding, organ failure, brain inflammation and death. A vaccine exists in India for KFD, but it requires multiple doses, elicits a short duration of protection, and its effectiveness is in question.
In a new study published Sept. 6 in Science Advances, researchers from NIAID’s Rocky Mountain Laboratories in Hamilton, Montana, describe how they used genetically engineered vesicular stomatitis virus (VSV) as the platform to develop a single-dose KFD vaccine that was safe and protective in mice and pigtail macaques, and is ready for clinical trials. They also showed that the same vaccine, known as VSV-KFDV, generated cross-neutralizing immune responses against AHF, results that need confirmation through efficacy testing in animal models.
VSV, an animal virus that primarily affects cattle, was used to create the world’s first approved vaccine (2019) against Ebola virus. VSV now has been successfully tested as an experimental vaccine that has generated protective immunity against more than a dozen different viral infectious diseases. Scientists use VSV to deliver targeted proteins from a viral pathogen of interest – such as KFD virus – to a host. The host then generates an immune response that provides protection should the host be infected with that viral pathogen.
According to the Centers for Disease Control and Prevention, KFD virus was first identified in 1957 from a sick monkey in the Kyasanur Forest in India. Since then, about 500 human cases have been reported each year, with fatality rates ranging from 3% to 5%. KFD has historically been limited to a specific part of India, but KFD virus has now expanded to new parts of India.
Alkhurma hemorrhagic fever virus was discovered in 1995 in a patient with bleeding and fever after slaughtering a sheep in Saudi Arabia, according to the World Health Organization. Little is known about the virus; a study published in 2022 states that 604 cases were reported in Saudi Arabia from 1995 to 2020.
B Bhatia et al. Single dose VSV-based vaccine protects against Kyasanur Forest Disease in nonhuman primates. Science Advances DOI: 10.1126/sciadv.adj1428 (2023).
B Bhatia et al. A live-attenuated viral vector vaccine protects mice against lethal challenge with Kyasanur Forest disease virus. NPJ Vaccines (2021).