In the 1990's, major concern arose over techniques have been developed to insert genetic material from one species of plant, bacteria, virus, animal or fish into another species with which it could never naturally breed. Risks include the creation of new micro-organisms alien to human experience, and the possibility that one of these might escape the confines of the laboratory and cause human disease. There is also growing evidence of horizontal transfer of genes between microbes. Viruses are routinely used now as the tools of genetic engineers, and lack of secure precautions or some laboratory malpractice could enable engineered viruses to be released. For example, one controversial technology requires the use of an antibiotic-resistant marker gene, which confers resistance to certain antibiotics in the people who eat genetically engineered foods. It utilizes strands of viral DNA which are stripped of the protein sheath that normally restricts viruses from jumping the species barrier. Without this barrier, scientists fear that the DNA will combine with other viruses, creating superviruses.
A potential hazard in current experiments derives from the need to use a bacterium like Escherichia coli to clone the recombinant DNA molecules and to amplify their number. Strains of E coli commonly reside in the human intestinal tract, and they are capable of exchanging genetic information with other types of bacteria, some of which are pathogenic to man. Thus, new DNA elements introduced into E coli might possibly become widely disseminated among human, bacterial, plant, or animal populations with unpredictable effects.
In Bulgaria, extensive field trials of bacteria- and virus-resistant tobacco have been grown since 1991, with no regulations and local public awareness. Other transgenic plants are being grown in field trials in Hungary and Russia.
Early experiments to breed larger-than-normal animal species by the use of the insertion of human genes have proved successful, with mice growing to twice their normal size at twice their normal rate. In Poland, genetically engineered carp with human growth hormone genes have been swimming in ponds for several years, separated from the wider environment only by a filter.
In 2000, scientists transferred a foreign gene into a rhesus monkey.