By Capt. Elizabeth Wanja, Walter Reed Army Institute of Research , Dr. Michael Turell, Virology Division at United States Army Medical Research Institute of Infectious Diseases , Lt. Col. Jason Richardson, Walter Reed Army Institute of Research
WASHINGTON, D.C. – The Army has paired with industry to develop a diagnostic device to detect the presence of the Rift Valley fever virus in mosquitoes.
The Military Infectious Diseases Research Program — one of the U.S. Army Medical Research and Materiel Command’s programs — and VecTOR Test Systems of Thousand Oaks, Cal., developed the device. The test will alert deploying troops to the presence of RFV, and will enable public health officials to prevent or mitigate the spread of the disease.
Rift Valley fever is a mosquito-borne viral disease that poses a significant health risk, primarily to livestock, but also to humans. Epidemiologists have been aware of Rift Valley fever, or RVF, since first isolating the virus in Kenya in 1931.
The new test kit — developed by VecTOR, with funding from the Small Business Innovative Research program and field testing funded by the Military Infectious Diseases Research Program — is a handheld dipstick assay that determines if field-collected mosquitoes are infected with the RVF virus.
The test provides results in less than 20 minutes, is easy to use, and doesn’t require the use of a laboratory with containment facilities. Additionally, the test does not require refrigeration, a particular concern in the tropics. As long as the dipsticks are kept within their original containers, they remain stable for two or more years.
The test kits allow early detection of infected mosquitoes, which enables military planners and public health officials to initiate preventive action, including mosquito control operations, administering animal vaccines, restricting the movement of livestock and warning against contact with infected animals. Officials can also distribute mosquito nets and repellents to the public and forewarn local hospitals.
On the military side, relevant agencies can issue such proven preventive measures as repellent and insecticide-treated uniforms and netting. Forces at increased risk include personnel operating in the Horn of Africa as part of Operation Enduring Freedom.
The human populations most vulnerable to RVF include farmers and herders who live near canals, rice fields and other wet zones where mosquitoes proliferate.
Mild cases of human RVF present with flu-like symptoms. In some cases, the patient can develop retinal degeneration, which may lead to blindness. In severe cases, the patient can develop encephalitis or even hemorrhagic complications, which kill up to half of those who contract it.
In 1997, 300 Kenyans died from what researchers suspect was a hemorrhagic form of RVF. Determining actual infection rates on the African continent can be challenging, as populations often live far from medical care. No treatments or licensed vaccines exist for human RVF, only palliative care; thus, accurate and reliable diagnostic methods are critical.
In animals, RVF causes acute hepatitis and spontaneous abortion in infected livestock, leading to steep mortality rates and substantial economic losses.
Once authorities declare an epidemic, they immediately prohibit all animal exports. Such bans cause further economic hardship, particularly for developing countries dependent on livestock for their livelihood. For Somalia, where livestock accounts for more than 80 percent of export earnings, extended bans can be devastating. Losses totaled $109 million during a ban there from February 1998 to May 1999 and another $326 million from September 2000 to December 2002.
Sick livestock infect other mosquito species, which then transmit the virus to humans. People can also contract RVF by coming into contact with the meat or blood of infected animals.
The validation process for VecTOR’s RVF virus assay was a joint effort among researchers from the Entomology Branch, Walter Reed Army Institute of Research; Virology Division, the U.S. Army Medical Research Institute of Infectious Diseases; the Kenyan Medical Research Institute and the U.S. Army Medical Research Unit, Kenya.