Twins are traditionally thought to be unlucky, even demonic. In some parts of Africa it wasn’t that many years ago that, after the birth of twins, they were apt to end up at the bottom of a deep well.

Superstitions of this sort did not deter the intrepid Van Tulleken twins from heading into the thickest jungles and swampiest forests in the Congo Basin. Both doctors, Christopher and Alexander van Tulleken went to Africa as part of a survey of medicine in the more primitive areas of the world.

The aim of their expedition to the Democratic Republic of Congo (Medicine Men Go Wild is currently being screened on Channel 4) and other remote locations is to find out whether the local practitioners’ approach to their patients had much in common with that of British doctors. Whatever the drugs or procedures used, the Van Tullekens were determining whether there is a universal commonality in the way that practitioners, whether Oxford-educated doctors or Congolese herbalists, approach their patients’ problems.

The Van Tullekens are fearless travellers: Christopher took part in the televised race to the North Pole a year or two ago. In Africa they were living among the Bayaka pygmies as they watched the local healer and herbalist, the equivalent of a village GP, treating his patients.

Disgusting and boring as the diet may have been on the trek to the pole, it could not have prepared the twins for their Congolese diet of roasted monkey, complete with a lengthy, gleaming white filarial worm, which they found festering in its middle. Filarial parasitic worms grow up to 2ft; among the diseases that they cause are river blindness and elephantiasis. The monkey that the hunters had caught was so ill that they caught it by grabbing its tail.

The two doctors were worried they had eaten the worms by mistake and had a brisk discussion about their chances of being infected by the worm or, even more alarming, of catching HIV or Ebola, both of which mutated into a human variant in this part of the Congo Basin.

In Britain HIV has not to any great extent spread beyond the groups of people who are known to be at high risk. There are now estimated to be 73,000 HIV positive people in the United Kingdom, of whom it is assumed that 21,600 are unaware that they have been infected.

In 2006, 7,800 new cases of HIV were reported, a similar figure to the number diagnosed in the previous year. This gives HIV experts some hope that the number may have stabilised. Of the people who are now being diagnosed, two out of five caught their infection in Britain, and of these, two thirds were homosexual men. There is a steady increase in the number of heterosexual HIV transmissions in Britain, especially among members of some ethnic minorities. There is also evidence that the number of people catching HIV from shared or dirty needles is increasing.

The latest figures give an interesting and rather unexpected slant on the distribution of HIV in Britain. As would be expected, the largest increase in the number of cases was in London but the proportional increase was lower in London than in all other areas. Over the past ten years the greatest proportional increase has been in eastern England and over the past year it was in Yorkshire and Humberside.

The good news is that, although HIV is not yet curable, and the virus cannot be eliminated from the body, modern treatment can reduce its presence to a minimum. This prolongs the life and good health of the patient. There is always the dread that the virus, which is unstable and mutates readily, may either mutate into a more virulent form that could be spread more readily or become more resistant to drugs now used.

Modern treatment involves using at least three drugs in combination. If a virus becomes resistant to one drug, it is likely to be vulnerable to the other two. Patients need to continue to take the drugs however well they feel and to take the other precautions involved in safer sex, including the use of condoms.

The drugs that attack HIV either prevent the virus from penetrating the host cell or from replicating once within the cell. Their discovery has produced such an improvement in the outlook for a patient that he or she should be able to count on having a life expectancy and quality of life as good as that of someone with diabetes.