Building a better Rift Valley fever vaccineJune 28, 2012
The African virus causes fever in humans, inflicting liver damage, blindness, encephalitis and even death on a small percentage of those it infects. It also attacks cattle, sheep and goats, producing high mortality rates in newborn animals and causing spontaneous abortions in nearly all infected pregnant sheep.
In 2000, outbreaks of Rift Valley fever in Yemen and Saudi Arabia showed that the virus could expand beyond its original range. With this and the rapid North American spread of West Nile virus in mind, infectious-disease experts have long feared that Rift Valley fever virus might come to the United States or Europe, causing major human suffering and devastating the livestock industry in affected areas.
"If Rift Valley fever virus were introduced to the U.S. or Europe, it would be a very scary situation," said UTMB assistant professor and Sealy Center for Vaccine Development member Tetsuro Ikegami, lead author of a paper on the vaccine work now online in the Journal of Virology. "To be ready to respond, we want a vaccine that can raise immune response very quickly in large animals and health workers. We also want a vaccine that will allow us to differentiate between infected and vaccinated animals."
Ikegami's first requirement - quick response - dictated the use of a so-called "live attenuated vaccine." A live attenuated vaccine is a strain of virus that has been weakened to harmlessness, but still has the ability to reproduce and provoke a robust immune response. Such vaccines often require only a single injection, increasing speed and convenience of administration.
A live attenuated vaccine for Rift Valley Fever virus already exists, a strain called MP-12. MP-12 produces a strong immune response in humans and livestock, but human safety trials of the vaccine have never been completed. Practical application of MP-12 faces other obstacles as well. For one thing, researchers worry that the vaccine retains a small amount of residual virulence. For another, they're concerned that the antibodies MP-12 evokes are identical to those produced in response to infection by full-strength Rift Valley fever virus. In an outbreak, public health officials would be unable to tell animals vaccinated with MP-12 from naturally infected ones, making it impossible for them to map the epidemic's spread and respond effectively.
To resolve these issues, Ikegami and his colleagues went to work on MP-12's genome, focusing on a segment designated NSs. When a Rift Valley fever virus enters a cell, NSs produces proteins that function like saboteurs. They attack two of the cell's key defense systems: the genetic mechanism that generates the antiviral protein interferon beta, and a protein called PKR, which suppresses viral protein production.
"We removed the NSs gene because we thought it would attenuate MP-12 further, and it would make it easy to differentiate infected from vaccinated animals - MP-12 without NSs wouldn't produce any anti-NSs antibody, thus giving a different antibody response from wild-type Rift Valley fever virus," Ikegami said.
Experiments with mice exposed to Rift Valley fever virus in UTMB's Robert E. Shope, MD Biosafety Level 4 Laboratory confirmed that the NSs-less strain remained a highly effective vaccine. But Ikegami was not satisfied.
"The neutralizing antibody response was slightly decreased, and I thought we could do better if we retained some of the function of the NSs," he said. To do this, the team introduced a gene for a "dominant negative PKR" - a molecule that would interfere with the cell-defending PKR protein, allowing the vaccine virus to multiply more freely. When they tested the new vaccine strain in mice, they found that it actually protected the animals better than MP-12.
"We got really good efficacy in mice, and we're hoping it will translate well to large animals," Ikegami said. "This has been a very successful project, with some great teamwork and major contributions from two postdocs, Olga Lihoradova and Birte Kalveram."
University of Texas Medical Branch at Galveston
Related Rift Valley Fever Current Events and Rift Valley Fever News Articles
Sierra Leone samples: Ebola evidence in West Africa in 2006
Analysis of clinical samples from suspected Lassa fever cases in Sierra Leone showed that about two-thirds of the patients had been exposed to other emerging diseases, and nearly nine percent tested positive for Ebola virus.
Newly identified natural protein blocks HIV, other deadly viruses
A team of UCLA-led researchers has identified a protein with broad virus-fighting properties that potentially could be used as a weapon against deadly human pathogenic viruses such as HIV, Ebola, Rift Valley Fever, Nipah and others designated "priority pathogens" for national biosecurity purposes by the National Institute of Allergy and Infectious Disease.
Turmeric Spices Up Virus Study
The popular spice turmeric packs more than just flavor - it shows promise in fighting devastating viruses, Mason researchers recently discovered.
Researchers find 'broad spectrum' antiviral that fights multitude of viruses
Viruses are insidious creatures. They differ from each other in many ways, and they can mutate - at times seemingly at will, as with HIV - to resist a host of weapons fired at them. Complicating matters further is that new viruses are constantly emerging.
Scientists uncover secrets of potential bioterror virus
Researchers at the University of Texas Medical Branch at Galveston have discovered a key tactic that the Rift Valley fever virus uses to disarm the defenses of infected cells.
Researchers examine role of climate change in disease spread
Ever since scientists first proposed that our planet might be experiencing widespread climate change, concerns have been raised about its implications for the spread of arboviruses - viruses carried by arthropods such as mosquitoes, midges and ticks.
'Deadly dozen' reports diseases worsened by climate change
Health experts from the Wildlife Conservation Society today released a report that lists 12 pathogens that could spread into new regions as a result of climate change, with potential impacts to both human and wildlife health and global economies.
NASA technology helps predict and prevent future pandemic outbreaks
With the help of 14 satellites currently in orbit and the National Aeronautics and Space Administration's (NASA) Applied Sciences Program, scientists have been able to observe the Earth's environment to help predict and prevent infectious disease outbreaks around the world.
Link between sunspots, rain helps predict disease in east Africa
The research, conducted by paleoclimatologist Curt Stager of Paul Smith's College in Paul Smiths, N.Y. and colleagues, can be used by public health officials to increase measures against insect-borne diseases long before epidemics begin.
Sunspot abundance linked to heavy rains in East Africa
A new study reveals correlations between plentiful sunspots and periods of heavy rain in East Africa. Intense rainfall in the region often leads to flooding and disease outbreaks.
More Rift Valley Fever Current Events and Rift Valley Fever News Articles