The World Health Organization says a shortage in trained health workers is reaching a crisis point worldwide and many countries will not be able to control a major disease emergency like an outbreak of avian flu. The WHO report says a further four million health workers are required in 57 countries, 35 of which are in sub-Saharan Africa. The WHO says without a major increase in the training of health workers, mortality rates from disease are likely to increase.

In its annual World Health Report, the World Health Organization this year has focused on the need for greater investment in the health workforce which it says is drastically under resourced.

The WHO says there is a direct correlation between the number of health workers and maternal and infant survival rates during pregnancy. The report also says the density of health workers is one of the key factors in reducing the spread and effects of infectious disease.

The WHO's Assistant Director-General of Evidence and Information for Policy, Doctor Tim Evans, says this is particularly critical in the control of HIV/AIDs.

"A shortage of human resources has replaced financial issues as the most serious obstacle to implementing national HIV treatment plans," he said.

The report says some the biggest problems are occurring in 36 African countries where the number of health workers per capita are the lowest anywhere in the world. It says this is due to migration of health workers to better paying jobs in developed countries and limited access to training facilities.

And, Dr. Evans says in sub-Saharan Africa the shortage of health workers is compounded by much a much higher disease rate.

"Africa has about 25 percent of the global burden of disease and only three percent of the workforce and less than one percent of the health expenditure, so Africa is way out on its own," he said.

And the report says the situation is becoming more critical as the population in developed countries ages and continues to increase in the developing world.

Dr. Evans says, without a major increase in the training of health workers, death rates during pregnancy and from disease will not improve and some areas of the health system are likely to get worse.

"If the workforce conditions deteriorate, as they may without very significant action, then it is conceivable that the current levels of health, for example infant health, may deteriorate," he said.

The WHO is recommending a 33 percent increase in the spending on health care in the critical countries over the next 10 years, half of which should be spent on training more than four million new health workers.

The report says this cost should be met equally by the worst affected countries and the international community.