With the avian flu hysteria spreading exponentially faster than the disease itself, investors have been stocking up on Gilead Sciences ( GILD), the maker of the influenza drug Tamiflu -- the product that appears to offer the best hope against the virus. Since the start of the year, Gilead's shares are up 49% compared with the 23% increase of the Amex Biotech Index and the almost 2% rise of the S&P 500. The company's market capitalization above $24 billion makes it one of the world's biggest biotechs. Recently the company has squabbled with marketing partner Roche over the rights for Tamiflu, but it remains at the forefront of any discussion about how best to prepare and protect against the bird flu. There's little doubt that Gilead has a leading position in this fight, but rather quietly, lesser-known and often very small companies like Biocryst Pharmaceuticals ( BCRX) and AVI BioPharma ( AVII) are stepping up their own attempts at easing spreading fears of a pandemic. The avian flu, primarily the H5N1 strain transferred from bird to bird, has been detected in more than 100 humans since the first reported bird-to-human case in Hong Kong in 1997. What's been garnering the most attention lately are worries that a mutant human-to-human version could be on the horizon. Now that the disease has leaked westward, with cases showing up in Romania and Turkey, biotech companies are scrambling to develop their own vaccines and treatments for the disease.