“If we want to stop the HIV epidemic, then we must know the mechanisms by which HIV uses human sex to spread,” said principal investigator Davey Smith, MD, MAS, associate professor of medicine in UCSD’s Division of Infectious Diseases and in the Veterans Affairs San Diego Healthcare System, and director of the CFAR Viral Pathogenesis Core.

It is known that most HIV infections worldwide result from exposure to the HIV virus in semen, made up of seminal cells and the fluid around these calls, called seminal plasma. HIV virus particles contain RNA and exist in the plasma, while infected seminal cells contain HIV DNA.

Using a method of comparing genetic characteristics, called phylogenetic analysis, the researchers studied a group of men who had sexually transmitted their HIV virus to other men. Phylogenetic models allow researchers to estimate the dates of origin of various groups of viruses; in this way the team was able to determine the source of rapidly mutating HIV viruses by analyzing the viral sequences extracted from the blood and semen of HIV transmitting partners. The team found that recipients shared a more recent common ancestor with virus from the seminal plasma than with virus found in the seminal cells of their source partner.

“Until now, it had not been established whether HIV RNA or DNA is transmitted during sex,” said Smith. “By analyzing the genetic differences between these two forms and the virus that was ultimately transmitted to newly infected individuals we found that it was the HIV RNA form present in seminal plasma that was transmitted.”

“The findings from this study will help direct prevention strategies to address the virus in the seminal plasma,” Smith said. “By knowing the origin of the transmitted virus, scientists may be able to develop new vaccines, vaginal microbicides and drugs to prevent the spread of sexually transmitted HIV.”

Smith notes that because the study involved pairs of men who have sex with men, the findings do not comment directly on HIV transmission to women. “Since the vast majority of women are infected with HIV by exposure to the virus in semen, HIV RNA in the seminal plasma is the likely culprit, but this needs to be confirmed,” he said.

Global warming affects countries like Haiti disproportionately

This important series of articles emerged from a conference on climate justice held earlier this year in New York City, co-hosted by West Harlem Environmental Action (WE ACT) and the Environmental Justice Leadership Forum on Climate Change. WE ACT, an active participant in the climate debate and the environmental justice movement, compiled the special issue under the leadership of Guest Editor Peggy Shepard.

The articles explore a range of topics, including “The Environmental Injustice of ‘Clean Coal’,” by Stephanie Tyree and Maron Greenleaf and “Climate Change, Heat Waves, and Environmental Justice,” by Jalonne White-Newsome and colleagues. The issue offers both a global perspective in “The International Dimension of Climate Justice and the Need for International Adaptation Funding,” by J. Timmons Roberts, and a focus on more local concerns, including “Minding the Climate Gap: Environmental Health and Equity Implications of Climate Change Mitigation Policies in California,” by Seth Shonkoff and coauthors, and “Best in Show? Climate and Environmental Justice Policy in California,” by Julie Sze et al.

“Facilitating Climate Justice Through Community-Based Adaptation in the Health Sector,” by Kristie Ebi and “U.S. Childhood Obesity and Climate Change,” by Perry Sheffield and Maida Galvez discuss the implications of global warming on human health and on healthcare utilization.

“During the last days of December 2009 the global community has waited with anticipation for the decisions among government leaders during the World Climate Change Meeting in Copenhagen,” said Sylvia Hood Washington, PhD MSE, ND, Editor-in-Chief of Environmental Justice, and Research Associate Professor at the University of Illinois at Chicago School of Public Health. “This rapt world attention about what is going to be done about the climate change problem exists because many understand that the problems that we face now and will face in the future from rising temperatures on our planet are inexorably tied to the equity of global health and not just global political/economics in a rapidly increasing industrialized world community. Readers will be immersed in the complexities of the imbalanced economy of human health in the context of recognized climate change in this first special issue of the Journal.”

Once infected with Wolbachia, Aedes aegypti mosquitoes also become less suitable as hosts for a form of malaria parasite that infects birds, said Scott O’Neill of The University of Queensland. (The mosquitoes under study aren’t natural carriers of human malaria.)

“This might be very powerful in reducing pathogen transmission by Aedes aegypti to humans, particularly for dengue and Chikungunya,” O’Neill said. “Together with the previously described life-shortening effects, the results suggest we might be able to have a major impact on disease.” That’s if it can be shown that the Wolbachia infection can invade natural mosquito populations, he added, a question his team is working on right now.

There is no vaccine or cure for dengue fever, which is a painful and debilitating disease suffered by some 50 million people worldwide every year. Dengue haemorrhagic fever, the more severe form of the disease, kills more than 40,000 people annually. Chikungunya usually isn’t fatal, but can cause symptoms similar to dengue. Human epidemics of Chikungunya have been cited in Africa, Asia and more recently in Europe, according to the CDC.

Wolbachia is already rampant in nature; the bacterium is estimated to infect up to 60 percent of all insect species. They are passed from mother insect to daughter or son through the insect egg and readily spread to high frequency in many species of mosquito. The species that are the major carriers of human disease don’t normally carry them, but that’s something O’Neill aims to change.

“We are currently conducting a series of experiments in contained outdoor greenhouse settings that are examining the ability of the Wolbachia infection to spread into natural mosquito populations,” he said. “If these prove successful, we hope to move to open field testing within the next one to two years.”

The idea would be to seed the natural mosquito population with Wolbachia by releasing mosquitoes that had been purposefully infected in the laboratory. Wolbachia bacteria have a good ‘trick’ to help ensure their spread, O’Neill explained. They are responsible for a developmental defect that makes the would-be offspring of pairings between infected male mosquitoes and uninfected females inviable. Since the bacteria is passed from mothers to their offspring, that means that infected females can actually have a reproductive advantage over uninfected ones, encouraging Wolbachia’s spread from one generation to the next.

O’Neill said his team is working on computational models to determine just how many infected mosquitoes would need to be released for the infection to take hold in the wild.

The researchers don’t yet know exactly how Wolbachia protects the insects from human disease-causing viruses. They have some evidence to suggest that the bacterial symbiont primes the insects’ immune system. Wolbachia may also outcompete the virus by limiting resources such as fatty acids inside the mosquitoes.

Even if the strategy works in a natural setting, there’s a chance the mosquitoes or the viruses could become resistant to Wolbachia’s influence over time.

” We can predict from evolutionary theory that selection will push the system in the direction of resistance, but we do not know the speed with which this might occur,” O’Neill said. “Even if it was effective for a few decades it might have a major impact on human disease.”