“Traditional explanations for the seasonal increase in dengue are not consistent with my experience in Thailand, Peru, and Puerto Rico.”-Doctor Thomas Scott
A recent study shows that long hot seasonal temperatures help the spread of Dengue. The areas of the world, where Dengue is becoming more prevalent, are areas that are not cooling off as they used to, and are subject to radical swings in warmer temps.
The study, “Impact of Daily Temperature Fluctuations on Dengue Virus Transmission by Aedes aegypti”, shows that without the usual cold seasons the mosquitoes, that spread the disease, stay alive much longer increasing their chances of catching Dengue from humans, and spreading it.
The study also showed that mosquitoes are less likely to spread disease during cooler temperatures, and more likely during hot weather: “…whereas transmission probability is estimated to be 0.11 at a constant mean temperature of 14 °C, it shows a 2.7-fold increase with a DTR [diurnal temperature range] of 20 °C.”
While many parts of the World are experiencing warmer than normal weather, here in Idaho our weather is much cooler than normal. That is keeping cases of West Nile virus way down, so far.
The big concern in Idaho is protecting horses. Horses are more susceptible to dieing from West Nile, than humans.
Local mosquito eradication officials are reporting that, so far, there’s a drop in West Nile infected mosquitoes, possibly due to the cooler weather. However, they pointed out that mosquitoes with West Nile usually show up in the later half of Idaho summers.
Another factor in favor of mosquitoes is flooding. Parts of Idaho have been hit with increased seasonal flooding, and the cooler weather (resulting in less evaporation) means there are large areas of standing water, perfect for mosquitoes.
Officials are already taking action by spraying insecticides on ponds, and asking property owners to drain standing water.
The Center for Disease Control and Prevention reports that Idaho, Oregon and Washington state are free of any West Nile cases (as of 26 July 2011). It could be due to the cooler than normal weather.
The CDC reports human cases of West Nile in the following U.S. states: Arizona, California, Georgia, Mississippi, South Dakota, Texas, Virginia, and Wyoming.
According to the most recent CDC Dengue HealthMap, there are no cases of domestically acquired Dengue fever within the United States.