Reverse the order of your single / double quotes.
<asp:HyperLink runat="server" NavigateUrl='~/DiseaseInfo/Syndrome.aspx?
SyndromeID=<%# Eval("SYNDROME_ID")%>&SpeciesID=<%# Eval("SPECIES_ID")%>'
Text='<%# Eval("SYNDROME_NAME").ToString()%>'>
</asp:HyperLink>
This normally doesn't matter at a JavaScript / HTML level but the correct quote for C# / VB is a double quote which should be used within the Eval()
method.
A slightly better approach would be to invoke a method to return this somewhat complex url:
<asp:HyperLink runat="server" NavigateUrl='<%# GetUrl() %>' />
protected string GetUrl()
{
return string.format("Syndrome.aspx?SyndromeID={0}...", Eval("SYNDROME_ID");
}