By Imogen Foulkes
BBC News, Geneva
A shortage of health workers around the world is having a serious impact on the ability to fight disease, the World Health Organization (WHO) has warned.
Poorer countries compete with rich ones for health workers
The WHO says the deficit is affecting 57 countries, most of them in the developing world.
It says the battle to fight diseases such as Aids, malaria and tuberculosis is being undermined as a result.
The figures have been published in a report which has been released to mark World Health day.
The statistics in the World Health report are stark.
The continents of North and South America have just 10% of the world's burden of disease but 37% of the world's health workers.
They spend over 50% of the total global health budget.
The continent of Africa has 24% of the world's disease, just 3% of the world's health workers and less than 1% of the budget.
Access to health care is a very unequal business.
Of the 57 countries which lack health workers, 36 of them are in sub-Saharan Africa - the very same countries which are struggling to cope with the AIDS epidemic.
The World Health Organization says the shortages are undermining not just the battle against deadly diseases like Aids, tuberculosis and malaria.
They are affecting childhood vaccination campaigns and basic care for pregnant women.
The reasons for the shortages are many, but money is key.
Rich countries need more doctors and nurses too, and salaries are higher than in Africa.
The WHO says developing countries are suffering a brain drain of health professionals.
The report calls for ethical recruitment policies for migrant health workers and international investment to help poor countries train more staff.
It says at the moment, the world is short of four million health workers, and 1.3 billion people lack even the most basic health care.