Dengue mosquito is a much smarter predator than thought, it uses a stealth mode to hunt humans even without smell, study finds

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When smell is gone, heat detection kicks in
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A new study shows that Aedes aegypti , the mosquito responsible for spreading dengue, yellow fever and Zika, can still find human targets even after losing its sense of smell. At the same time, Indian scientists have identified a specific group of immune cells that could reshape the understanding of how the body responds to dengue infection.Researchers at Rockefeller University experimented with Aedes aegypti by disabling its primary olfactory gene, Orco, which helps the mosquito detect human odours. They expected this would impair the mosquito's ability to hunt humans.Instead, the mosquito adapted. According to the study published in Science Advances, even without its sense of smell, the mosquito could still locate humans by sensing body heat. The researchers discovered that Orco mutants used their forelegs, not just their antennae, to detect skin temperature.This was linked to a heat-sensitive receptor called Ir140. When Orco was removed, the mosquito compensated by increasing the activity of Ir140, a process known as upregulation. This kind of sensory compensation is common in humans, such as improved hearing among people with visual impairments. The same pattern in mosquitoes points to how evolution has shaped them into efficient hunters.However, it was only when both Orco and Ir140 were knocked out that Aedes aegypti lost its ability to sense human heat.In a separate study, Indian scientists at the National Institute of Immunology (NII) and AIIMS Delhi, along with international collaborators, have identified a key group of immune cells that play a central role during dengue infection.These immune cells — a subset of CD4+ T cells — are known as PD-1+CXCR5–CD4+ T cells. They activate B cells, which are responsible for producing antibodies. This process is mediated by a signaling molecule called IL-21.Unlike conventional follicular helper T cells that work within germinal centres of lymph nodes, these newly identified peripheral helper cells operate outside them — in extrafollicular niches — and may even reach inflamed tissues.This discovery provides new insight into why antibodies behave unpredictably in dengue. Antibodies can protect the body, but in some cases, especially among individuals with past dengue infections, they can worsen the disease through a process known as antibody-dependent enhancement (ADE).The study also found that PD-1+ helper T cells are not uniform. They divide into IL-21-producing helper cells and cytotoxic cells. Some may remain in the body as memory cells, possibly contributing to long-term immune response.Researchers are still trying to determine whether these cells offer protection or increase risk during future dengue infections. If understood better, these cells could help develop targeted vaccines against dengue.Despite advancements in science, the mosquito remains one step ahead. Swarnadip Ghosh, a researcher from the National Centre for Biological Sciences (NCBS) in Bengaluru, described the mosquito's ability in verse:'When scent fades out,the mozzie's not beat,She hunts you down bythe stink of your feet.No nose? No problem —she's got legs that feel heat,And still thinks yourblood is a five-star treat.'(The article was orignially published in TOI)