Health risks in the Sierra Nevada?

@HealthMed Every year millions of people visit beautiful Yosemite and Lake Tahoe in the Sierra Nevada of the Western USA. The individual risk of contracting a serious infection is low, however there are several rare but important public health risks. These range from minor nuisance from irritating bites by ‘no-see-ums’ to a range of serious infections.

Yosemite National Park

While visiting there in mid-August, there were reports in the US press of 2 deaths from hantavirus infection, attributed to contact in the Yosemite National Park area with deer-mice as the carrier. There are also notices posted at other beauty spots in the Sierra Nevada not to handle small animals; ground squirrels and other small mammals were reported to harbour plague; ‘no-see-ums’ to be vectors for West Nile virus infection (around half those affected developing an encephalitis syndrome); and ticks to carry risk of acquiring Lyme disease or the protozoal infection, babesiosis. The Centers for Disease Control in Atlanta report that these infections are rare, however urgent treatment for infected individuals may be needed, with public health measures important.

In practice, in mid-August, whether or not due to insect spray provided by a friendly bed and breakfast host, there was little insect activity evident - but that's the nature of 'no-see-ums'. There were plenty of small mammals keen to share visitors’ food – including grey squirrels to golden-manteled ground squirrels and marmots.

And why the lag in international media coverage until the end of August? The regional California press appear to have begun to cover the hantavirus story around 16^th August. The BBC and other UK media began reporting the news from 28^th August, in part perhaps because US public health authorities had begun to alert Yosemite visitors potentially at risk, typically those who had used tents and tent-cabins into which culprit rodents may have entered.

What is hantavirus? It is one of a family of viruses. Hantavirus infection can affect the skin, lungs, kidneys and other organs. Since the first recognized major outbreak, affecting several thousand US soldiers in the 1950s during the Korean War in the Hanta River region of South Korea, the virus has been detected in many parts of the world, from elsewhere in SE Asia to Scandinavia, mainland Europe and the USA. The type of small rodent carrier varies with geography. Clinical illness appears be rare, with however potentially severe illness in those who are affected, and a high mortality rate, treatment based on supportive measures.

Syndromes caused by hantaviruses differ across geographical regions. Typically old world hantaviruses affect predominantly the skin and kidneys, causing a ‘haemorrhagic renal syndrome’. New World viruses typified by the ‘Sin Nombre Virus’ first described in 1993 usually cause a serious pulmonary syndrome, with around 1-6 weeks incubation period.