the stages of that carry pathogenic microbes and long survival of these microbes in specialized niches within the tick, such as within cells of the salivary glands or the gut. In a population of Rhipicephalus or Hyalomma ticks feeding on cattle in which Theileria species of protozoa circulate and cause theileriosis, the ticks act as long-term reservoirs of the protozoans. In addition, some species of protozoans (within the Theileria and Babesia genera), are able to infect ticks even when they exist in the blood of their hosts at such a low level that no signs of disease can be detected. This is known as a carrier state of infection. These pathogenic protozoa can be detected circulating in populations of the cattle hosts and tick vectors with only low levels of detectable disease in the cattle caused by the protozoa. Any situation like this - with prevalent infection or infestation but little disease - is called endemic stability. It is possible that this can be exploited for better control of tick related diseases by use of breeds of cattle with good ability to acquire resistance to both the ticks and the protozoans. However, there are commonly situations where the potential benefits of endemic stability to disease are difficult for farmers to use effectively. The farmers may prefer to rely more on direct tick control, and drugs and vaccines against the protozoans. Drug treatment against microbes Antibiotics with efficacy against bacterial pathogens transmitted by ticks include tetracycline, penicillin, and doxycycline. Against Babesia protozoa are imidocarb and diminazine, both of which can be used to treat patent clinical infections. Against Theileria are parvaquone and halofuginone, both effective for clinical cases. These drugs are usually administered to treat diagnosed cases, but the timing of treatment then becomes critical. Problems with drug treatment include the development of resistance by the microbes and cost. Also, treatment does not necessarily fully clear infections, and this may lead to persistent subclinical infections that remain infective to more ticks (carrier infections); this may be considered unsafe in some situations. Vaccination against microbes and ticks Vaccination against An. marginale is done using live strains of the cross-reactive An. centrale. Vaccines are available on a commercial basis to immunize cattle against Babesia bovis. This is made by serial infection of calves to attenuate the virulence of the strain of Babesia, followed by splenectomy to produce many of the piroplasm stage in