For the purposes of section 1131 of this title, and subject to the provisions of subsections (b) and (c) of this section, any veteran who served for six months or more and contracts a tropical disease or a resultant disorder or disease originating because of therapy administered in connection with a tropical disease, or as a preventative thereof, shall be deemed to have incurred such disability in the active military, naval, air, or space service when it is shown to exist within one year after separation from active service, or at a time when standard and accepted treatises indicate that the incubation period thereof commenced during active service.

Service-connection shall not be granted pursuant to subsection (a), in any case where the disease or disorder is shown by clear and unmistakable evidence to have had its inception before or after active military, naval, air, or space service.

Nothing in this section shall be construed to prevent the granting of service-connection for any disease or disorder otherwise shown by sound judgment to have been incurred in or aggravated by active military, naval, air, or space service.