According to the World Health Organization, there are around 50 million cases of dengue fever around the world every year. About two and a half billion people, two fifths of the world's population, are at risk. The disease is now spreading, along with the mosquitoes that carry it, into areas like Texas, in the United States -- far from the virus's tropical breeding grounds. Scientists at an independent research foundation in San Antonio, Texas have developed a new line of study they say shows promise in fighting the often deadly disease.
This mouse has a lot in common with its handler because it carries some human cells that allow it to be infected with dengue fever, just like people.
These so-called humanized mice were injected with human stem cells from umbilical cords discarded after women gave birth at local hospitals.
They are a crucial part of the dengue study being carried out by Rebecca Rico-Hesse and her colleagues here at the Southwest Foundation for Biomedical Research. "We have basically reconstituted the human immune system in these mice and it is only because they have these immune system cells that they can get infected and show symptoms of dengue fever," she says.
By infecting the mice with strains of the dengue virus, investigators can study how the disease takes hold and what factors might cause the more serious and often deadly dengue hemorrhagic fever.
In people, the disease found in tropical and subtropical climates causes an uncomfortable rash, fever, headaches. The more serious cases will include bleeding under the skin, shock and death. There is no treatment or cure.
Rico-Hesse and her colleague, Javier Mota, just published a report showing how their study method can help lead to better treatments by identifying the specific viral strains that are most dangerous. "In this report we present results of eight different virus strains and we show that the ones that have been associated with the more severe epidemics and the ones that cause hemorrhagic fever in patients are actually of a specific genetic variant," she says.
Mosquitoes normally spread dengue. When they bite, they inject certain proteins into the skin which does not happen when mice are artifically injected in the lab. So, the scientists are breeding mosquitoes that will bite the mice and transmit the disease. "If you are just, you know, injecting it in with a syringe, you are missing out on all those salivary gland factors and all the things that happen during a natural infection that might either speed up the infection rate or decrease the infection rate," she says.
Rebecca Rico-Hesse has worked extensively among those stricken by dengue fever in Latin America. "I have had the opportunity to go to many of the countries and see the patients, even children dying in the hospitals…. So it has given me a sense of urgency to work more," she says.
Although effective vaccines or antiviral drugs for dengue may still be a long way off, researchers here say they are taking important steps that they hope will one day minimize the suffering caused by this illness.