Some can transmit diseases. For example, the pig louse may carry swine flu viruses or swine pox. Flies can mechanically transmit bacteria and viruses from one pig to another, directly in the case of biting flies or indirectly by contaminating feed. Flies can also transmit infections from one pig farm to another if they are less than 3km (2 miles) apart. In South East Asia mosquitoes can transmit the deadly Japanese B. encephalitis virus from pigs to people. In Africa they transmit African swine fever virus from pig to pig.

Mites, lice and ticks are important (Fig.11-13) because of their effect on growth, feed efficiency and spread of disease. They are a nuisance to the pigs and pig attendants.