Important note: Information in this article was accurate in 2000. The state of the art may have changed since the publication date.
Mail and Guardian (Johannesburg) - September 15, 2000
Denise Ford
He says: "But the notion that immune deficiency is only acquired from a single virus cannot be sustained ... I am saying that you cannot attribute immune deficiency solely and exclusively to a virus," and later, "TB [tuberculosis], for example, destroys the immune system and at a certain point if you have TB you will test HIV- positive because the immune system is fighting the TB which is destroying it."
Immune failure is caused by a variety of conditions, including HIV, leukaemia, chemotherapy, organ transplantation, as well as inherited conditions. These can lead to a predictable and catastrophic failure of the immune system if left untreated.
TB commonly complicates any of these conditions, as do fungi, other bacteria and cancers. Poverty makes them all worse. But the causes of Aids remain the causes, and don't require poverty or TB to give you the syndrome.
HIV is a virus which is visible under an electron microscope and can be grown in a laboratory. It is an infectious physical entity causing Aids and immune failure in almost all infected individuals. It is not a hodge-podge collection of symptoms, as the president seems to allege.
Patients with TB, but without HIV, do not display the opportunistic infections associated with immune deficiency.
Mbeki says: "... TB is the thing that destroyed the immune system in the first place." This is inaccurate. TB kills by destroying tissue, mainly in the lungs, and does its damage by actually activating the immune system rather than suppressing it.
TB may cause immune dysfunction, but alone does not result in immune failure. Then the president said "... if you have TB you will test HIV- positive" - a statement that is equally problematic.
Humans react to any infection by manufacturing antibodies - proteins which mark the offending organism for killing and clearance by specialised cells. These antibodies are highly specific for each organism. Most HIV tests used by South African laboratories involve detection of antibodies to HIV.
Most people who grew up in Africa had TB as children but controlled it spontaneously, and probably put it down to flu.
They may have had TB, but they don't all have HIV.
With antibody tests, blood is added to the test solution, causing clumping or colour changes if HIV antibodies are present.
TB's proteins are very different and won't respond to the HIV test. Theoretically cross reactivity can occur, but it is extremely rare, if it occurs at all, and it can be caught by doing a follow-up test.
The initial HIV antibody tests were not perfect. However, with each successive generation of tests, the false negative and the false positive rates have improved. HIV tests have a more than 99% chance of being accurate, whether you have TB or not.
South African scientists are world experts on TB, and are now developing similar expertise in HIV and immunology. These are the people South Africans should be listening to.
Denise Ford is a medical doctor
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