AIDS is the biggest threat to development in Botswana, where about one in five of the 1,5-million population are Hiv positive, a government-sponsored study said on Monday. The report said nearly half of all households in Botswana probably have at least one member infected with the virus. Around one-quarter of households could be expected to lose an income earner during the next 10 years, fuelling a rapid increase in poverty, the report said.