Bovine spongiform encephalopathy ( BSE )

BSE, a condition seen generally in adult cattle of either sex was first recognised in 1986 in the UK, where it now infects greater than 55% of milking herds. The numbers are highest in Southern England where more than 60 cases have been reported in a single herd but are generally spread throughout the British Isles, often as less than 3 cases per herd of 100 cattle per annum. It has been reported now in Oman, Switzerland, France, Germany, Canada, Denmark, Portugal, and Italy but these cases are probably associated with the export of either infected animals or infected meat and bone meal for bovine feed from the UK. It is difficult to explain the cases in Portugal in that many are the offspring of cattle exported from the UK, whereas their mothers are apparently not clinically infected. The disease is thought to have been derived either from the change in the manufacture procedure of meat and bone meal (for bovine consumption) or from the inclusion of an uncomon bovine case of spontaneous BSE in bovine food in approximately 1978-1980. Claims have been made that this is not a new disease; in the past, although not histologically diagnosed, it has been seen in approximately 1 cow in 20,000 to 30,000. The rapid increase of the disease (850 cases reported per week in 1994) is probably due to the inclusion of undiagnosed cases of BSE in the meat and bone meal used for bovine food. This was stopped in the UK in July 1988, but the meal was simply exported to other countries by its manufacturers (this has now been stopped). BSE has now been transmitted to cattle, mice, sheep, and goats both orally and by inoculation, and to pigs, marmoset monkeys but not hamsters merely by inoculation. Over 18,000 cases have been developed BSE although they were born after the ban of oral infectious material being present in their food. It is still unclear whether the cattle become infected directly from the food that they eat or from asymptomatic mothers that have done this.The possibility that an environmental factor other than the BSE infective agent may be involved with the transmission of BSE has been suggested due to the relatively low incidence of disease on 'organic' farms and organosphorus insecticide use has been suggested as being involved. The long incubation period (presumed to be more than 2 years and most commonly 5 years) means that case numbers have appeared to decrease accoreding to MAFF statistics since 1994. There is argument about the validity of this data. Clinically, the cow appears alert but agitated, anxious, and apprehensive. As the disease progresses, however, the animal starts to take a wide base stance, the abdomen is drawn up and the gait becomes abnormal and exaggerated and it gives rise to tumbling and skin wounds. Fine muscle contractions are seen involving small muscle groups over the surface of the neck and body with occaisional larger muscular jerks. The animal loses weight and is taken to frenzied movements including aimless headbutting. The possibility that BSE may be infectious to humans was considered to minimal in the UK until November 1989, when the feeding of bovine tissue, lymphoid tissue, spleen, thymus or gut (from cattle over the age of 6 months) to humans was banned. All animals that show signs of BSE in the UK must now be slaughtered and disposed of by incineration or burial. Beef in the UK would be expected to carry a lower titre of the infectious agent at the present time, but the larger amounts eaten by humans and the long human lifespan make its safety unclear.