According to recent research, it is true that bug zappers can end up transmitting the diseases carried by the insects they zap.
Two Kansas State University researchers, James Urban and Alberto Bruce, carried out a study of this effect. They contaminated house flies with bacteria or viruses either externally (by way of an aerosol spray) or internally (by feeding them sucrose solutions containing the bacteria or virus). They then released the flies into a chamber where a bug zapper was mounted and sampled the air at various distances from device.
This content is not compatible on this device.
What they found was that the air around the bug zapper was contaminated with bacteria and virus particles from the electrocuted flies (externally-contaminated flies released more bacteria and virus particles than internally-contaminated flies). Other research has shown that bug zappers can spread a mist containing insect parts up to about 7 feet (2 m) from the device. Urban and Bruce concluded that bug zappers pose a health risk because of the release of bacteria, viruses and potential allergens (insect parts) into the surrounding air.
Therefore, if you plan to use a bug zapper at your next picnic or barbecue, it is probably wise to place it at least 12 feet (3.6 m) away from areas where food is prepared or eaten and where children play.
Here are some interesting links: