Medical Genetics Other viruses, such as cytomegalovirus and herpes simplex, can also cause problems. Bacteria such as salmonella, present in undercooked meat (especially chicken), and listeria(found in some cheeses), can cause problems for the continuation of the pregnancy(rather than birth defects)Medical Genetics Other viruses, such as cytomegalovirus and herpes simplex, can also cause problems. Bacteria such as salmonella, present in undercooked meat (especially chicken), and listeria (found in some cheeses), can cause problems for the continuation of the pregnancy (rather than birth defects)