Transmissible Disease

an infectious or parasitic disease of man and animals whose causative agent is transmitted by arthropods. The transmission of the causative agent is either mechanical or specific; it is specific if the causative agent reproduces and/or undergoes its cycle of development in the body of the transmitter. The causative agent is transmitted through the bites of gnats (insects of the suborder Nematocera and the family Phle-botomidae), as well as of fleas, mites, and ticks. Transmission also occurs when infected discharges from the transmitter come in contact with the skin and mucosa.

In man, transmissible diseases may be obligate or facultative. The causative agent of obligate transmissible diseases is conveyed exclusively by transmitters, as in malaria, yellow fever, and tick-borne relapsing fever. The causative agent of facultative transmissible diseases is transmitted by droplets, through the digestive tract, or directly from one person to another, as in tularemia, plague, and anthrax. Obligate transmissible diseases are infectious diseases of the blood, since the causative agent enters the body by means of the blood and lymph and also reproduces in them. Most transmissible diseases are naturally endemic.

Transmissible diseases of animals are seasonal and also enzootic, that is, they are confined to a limited area or climatic and geographic zone. When the causative agent is transmitted by flying insects, transmissible diseases of animals are generally more widespread than when the causative agent is transmitted by mites and ticks. Obligate transmissible diseases of animals include infectious catarrhal fever of sheep, hydropericarditis, infectious equine encephalomyelitis and infectious equine anemia, African horse sickness, Rift Valley fever, Nairobi disease, louping ill, and viral pustular dermatitis. Facultative transmissible diseases of animals include anthrax, African swine fever, tularemia, and other septic infections.

Transmissible diseases are prevented by protecting persons and animals from bloodsucking arthropods; this may be achieved by moving animals to new pastures or to stalls, or by using insect repellents. The diseases may also be prevented by destroying transmitters and rodents, by carrying out land-reclamation measures in areas where transmitters breed, and by immunizing persons and animals in cases when effective immunization measures have been developed.