also be transmitted by biting flies, or by blood on injection needles (iatrogenic transmission). A characteristic of diseases caused by tick-transmitted microbes is that herds or flocks of livestock often acquire effective levels of immune resistance to both the vector ticks and the microbes, so outbreaks of acute disease tend to be rare. This stability is often due to immunity to the microbes developing as a result of survival through early infection from ticks carrying small infective doses of the microbe, the epidemiology of infections with Babesia species of protozoa is a well described example. The ticks are often constantly present and long-lived. Acquisition of immunity may be aided by the protection of antibodies in the mother's colostrum (first milk). At least one microbe causing disease associated with ticks is not transmitted by the ticks. The skin disease dermatophilosis of cattle, sheep, and goats is caused by the bacterium Dermatophilus congolensis, which is transmitted by simple contagion. When Amblyomma variegatum adult ticks are also feeding and causing a systemic suppression of immunity in the host, then dermatophilosis becomes severe or even fatal. Viral diseases The virus of Nairobi sheep disease in East Africa is transmitted by Rhipicephalus ticks. African swine fever is naturally transmitted between wild species of the pig family by feeding of Ornithodoros moubata group ticks. This pattern of transmission can expand to include domestic pigs. However, within groups of domestic pigs, the virus can also be transmitted by contagion. Crimean-Congo hemorrhagic fever virus is transmitted between many mammal species by Hyalomma truncatum, Hyalomma rufipes, and Hyalomma turanicum over a wide area of Africa, Europe, and Asia. In cattle and sheep, it causes mild fever and its main importance is when it spreads to humans (zoonosis) by feeding of the larvae or nymphs of these ticks. There are other viruses transmitted by ticks between wild animals and that have zoonotic importance when humans also become infected. The epidemiological pathways of these viruses can also involve domestic animals, if only by being hosts that add to the size of the tick population. Examples include the viruses that cause Tick-borne encephalitis, and Kyasanur Forest disease. Bacterial diseases Borrelia bacteria are well described elsewhere in association with Ixodes ticks for causing Lyme disease in humans, but this disease also affects domestic dogs. Borrelia anserina is transmitted by Argas persicus to poultry, causing avian borreliosis in a wide spread of tropical and