Asymptomatic dengue-infected humans can transmit the virus to mosquitoes

A drawing of a female Aedes aegypti mosquito (Credit: E.A. Goeldi)

An estimated 3.9 billion people in 128 countries are at risk of dengue virus infection. Of the estimated 390 million dengue infections that occur each year, 96 million will manifest clinically with flu-like symptoms including fever, headache, nausea and muscle and joint pain. Unlike the flu virus, dengue virus cannot be transmitted directly from person to person. It instead relies on an insect vector, the mosquito Aedes aegypti. Female mosquitoes contract the virus when they bite and feed on an infected human. After a period of four to ten days, the virus disseminates to various tissues in the mosquito, where it remains for the rest of the mosquito’s life. At this point, the mosquito is infectious and can transmit the virus through its saliva and bite.

Earlier studies showed that the time during which dengue virus-infected humans can transmit the virus to mosquitoes coincides with the onset of clinical symptoms and an increase in viral load in their blood. These observations led to the assumption that infected, asymptomatic humans are so-called “dead-end hosts” for the virus because their viral levels are so low as to make them noninfectious to mosquitoes, essentially breaking the transmission chain.

In a new paper published last week in the Proceedings of the National Academy of Sciences, an international group of researchers challenged a long-held assumption that asymptomatic patients infected with the dengue virus are not infectious. The team sought to experimentally test the assumption that asymptomatic people are noninfectious and to determine how human-to-mosquito transmission varied with timing of symptom onset. Continue reading

Saving brains: malaria in pregnancy leads to cognitive deficits in offspring

The malaria clinic at Nalufenya Children’s Hospital in Jinja, Uganda (Credit: Chloe McDonald)

In the global effort to eradicate malaria, the focus has often been on the number of lives saved—through insecticide-treated bed nets, artemisinin-based therapies, vector control and other strategies. Equally important in this fight is the concept of saving brains, particularly in young children.

Malaria is caused by an infection with the parasite Plasmodium falciparum and can manifest as either an uncomplicated or severe disease. The most severe neurological complication is cerebral malaria, a disease that disproportionally affects young children because they have not yet developed immunity against Plasmodium parasites. More than 785,000 children under the age of nine living in sub-Saharan Africa are affected by cerebral malaria each year. The idea of saving brains becomes especially relevant in this population because cerebral malaria can have long-lasting effects on the cognitive function of these children. An early study found that children who developed cerebral malaria were roughly three and a half times more likely to have a cognitive deficit than children who did not have malaria. Importantly, researchers observed this difference two years after the initial episode of cerebral malaria and long after the disease itself had been treated.

If exposure to malaria at a young age could have long-lasting effects on the cognitive abilities of children, what happened when that exposure happened much earlier? Like during pregnancy? In a new study published in PLoS Pathogens, a team of researchers led by Dr. Chloë McDonald and Dr. Kevin Kain showed that malaria in pregnancy leads to cognitive impairments in the offspring that persist into adulthood. Continue reading

Integrating self-collecting HPV DNA testing with community health worker programs increases cervical screening coverage

This past weekend, I attended a conference on health and high politics examining the role of politics, global partnerships, and innovation in health equity and security. Two talks at the end of the day stood out for me. The first was by Dr. Leslie Davidson, a professor of epidemiology and pediatrics at Columbia University, and the second was by Dr. Ophira Ginsburg, a medical oncologist at Women’s College Research Institute in Toronto who specializes in women’s health equity and global cancer control.

A common thread in both talks was the increasingly important role of community health workers in meeting the challenges of delivering health services to underserved populations. During Dr. Davidson’s talk, she mentioned a recently published study from Argentina demonstrating the effectiveness of using community health workers as part of an integrative program to promote cervical cancer screening. Ever intrigued, I decided to read the original paper and share it here.

In the study published in Lancet Global Health, researchers found that when community health workers offered self-collecting HPV tests to women, participation rates increased four-fold. Human papillomavirus, or HPV, DNA testing is emerging as a viable alternative to Pap smears in low-resource settings. Earlier studies have shown that HPV DNA testing is as sensitive as conventional Pap smears in detecting cervical disease. An additional benefit of HPV DNA testing is the potential for self-sampling, which allows women to collect their own vaginal swabs in the comfort of their own homes. Continue reading