Mary is driving to work with her six-year old son Michael and her three-year old daughter Joan on the back seat of the car. As Mary looked in her rear mirror, she sees Michael playing with a gun, with his finger on the trigger. Horrified, Mary tries to quickly pullover. But in an attempt to avoid a pothole, she spins unto oncoming traffic and had a head-on collision. Luckily, Michael did not pull the trigger, but Mary lost the pregnancy she was carrying in the accident. What caused Mary’s pregnancy loss? Was it Michael who managed to find his father’s gun? Was it Michael’s father who was reckless with the safekeeping of his gun? Was it the municipal manager who did not fix the potholes on the road? Was it Mary who was not wearing her seatbelt while driving? Or was it a combination of some or all of the above?
There is no gainsaying that Former President Thabo Mbeki is one of the most respectable African leaders of our time. He is certainly one of my best. Of course, no leader is perfect, and Mr Mbeki is not perfect. One of the areas he is adjudged to have performed poorly is the way he handled the HIV debacle in the early days that the epidemic could have been curtailed. It is easy to understand the reasons for his position - the history of South Africa and the apparent readiness of more developed countries to manipulate and exploit Africa at the slightest opportunity, whether through her natural resources, healthcare or otherwise.
While many of us have chosen to forget his shortcoming in this area, Mr Mbeki seems to continue to maintain his position that HIV is not the cause of AIDS. He maintains that, “A virus cannot cause a syndrome. As represented by the letter 'S' in AIDS, the syndrome includes a collection of diseases, according to the US Centres for Disease Control and others.” He says that, according to the Oxford English Dictionary, a syndrome means, "a set of concurrent things,” which is true. So he does not believe that the immune deficiency (in AIDS) can be acquired from a single virus.
Although Former President Mbeki’s focus appears to be on the word syndrome, the bone of contention is really on understanding of causality. I have decided to use this article to explain the term cause in the medical context. Perhaps I will use a subsequent article to respond to some of his observations from the country’s causes of death reports.
In health, the cause of a disease is an event, condition, characteristic or a combination of these factors which plays an important role in producing the disease. Implicit in this definition are many conceptions, one of which is the allowance for multifactorial causation. The concept of multifactorial causation can be difficult for the layman to grasp. It is difficult for many people to conceive that an outcome can be caused by a number of factors, and even more difficult is the fact that the causative factors do not all have to operate at the same level. Perhaps, in the example of Mary’s pregnancy loss above, your view of what caused the loss might lean on who you are – a civil engineer, traffic officer, lawyer or a superstitious person. There are two other important concepts in causality. The first is understanding the causal chain of a disease, while the second is understanding whether a cause is necessary or sufficient.
Assume that a young man Peter has a sedentary lifestyle with very little activities, and by 40 he is obese and develops high blood pressure which then leads to stroke. Surely, it would not be wrong to say Peter’s stroke was caused by his sedentary lifestyle or that Peter’s stroke was caused by obesity. Both lifestyle and obesity are causes of stroke, albeit acting at different levels. One is distal (downstream) while the other is proximal (upstream).
Although Mr Mbeki is quite correct in his definition of syndrome (as involving many conditions), there is a need to appreciate the pantropic nature of the virus in penetrating different tissues of the body. More importantly, there is a need to appreciate the role the virus plays in setting off the cascades that leads to the syndrome, by hampering the very immune system that was meant to fight those conditions. As stated earlier, the cause of a disease can be downstream or upstream. In the case of AIDS, the syndrome we see only manifests, because the HIV causes it.
Necessary or sufficient cause:
The other concept in causality is whether a cause is necessary or sufficient for a disease to occur. A necessary cause is one that must be present for the disease to occur while a sufficient cause is one that will invariably lead to the disease when present. These concepts are well captured in Koch’s postulates for causation of infectious diseases and in the Bradford-Hill criteria for causality. For the syndrome called AIDS to manifest, HIV has to be present and its effects can be measured by viral load and CD4 count which are demonstrable.
Former President Thabo Mbeki has frequently advanced factors like poverty and malnutrition as explanations for AIDS. Of course, it is important to pay attention to these factors as they can affect the rate of disease progression, but they are neither necessary nor sufficient causes of AIDS. HIV, on the other hand, is not just a cause (or a contributory cause) of AIDS. It is the cause of AIDS. AIDS manifest because of the effects of HIV. It is true that HIV is not sufficient for the disease as not everyone who has HIV infection develops AIDS, in the same way as not everyone infected with tuberculosis germs develops the disease. HIV is a necessary cause of AIDS. Without HIV, there is no AIDS.
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