Former South African President Nelson Mandela remains in a critical though stable condition, President Jacob Zuma said Thursday, after visiting the Pretoria hospital where Mandela is being treated.

The former South African president and anti-apartheid leader, who is one week shy of his 95th birthday on July 18th, has been fighting lung infections for the past several months since he was originally admitted to the hospital on June 8th.

Several of his fellow anti-apartheid activists lamented his absence during their 50th anniversary celebration Thursday of the 1963 raid on the Liliesleaf farm in Johannesburg. During the police raid, many of Mandela's anti-apartheid comrades and African National Congress (ANC) leaders were arrested, Mandela already being in prison at the time.

Though he is 94 years old, many South Africans find it difficult to accept that their country's hero, who withstood 27 years in prison after receiving a life sentence by South Africa's apartheid government, is bedridden and monitored 24/7 by doctors.

Ahmed Kathrada, one of Mandela's closest fellow political prisoners who has known the leader since 1946, spent a few minutes by Mandela's bedside. According to the Associated Press, it was a traumatic experience for Kathrada to see his former comrade in such a fragile state.

"All the years that we knew him, we knew him, somebody who was very conscious of his health, somebody who exercised in and outside of jail, regularly, and here you see a person who's different...a shell of himself," Kathrada, 83, said in an interview with The Associated Press.

"[Mandela] was a boxer, he was a gymnast, he was a very strong person," Kathrada said. "In prison too, when we were working at the quarry with pick and shovels, we found difficulty... but he was strong enough to adjust to that quickly."

Fight Against TB

Mandela originally contracted tuberculosis in prison in 1988. After surviving the illness and being released from prison in 1990, he has spoken about the importance of fighting the disease as well as HIV/AIDS, both of which are linked and affect a large amount of people in sub-Sahara Africa.

Mandela said he was lucky he was diagnosed and cured of TB before it advanced to a stage where holes would form in the lungs.

According to Jack C. Chow, assistant director-general for HIV/AIDS, Tuberculosis and Malaria at the World Health Organization, people with HIV are 50 times more likely to develop tuberculosis due to a weakened immune system. Nearly 50% of people with HIV in the developing world end up contracting tuberculosis.

"We cannot win the battle against AIDS if we do not also fight TB. TB is too often a death sentence for people with AIDS," Mandela said at the 15thInternational AIDS Conference in 2004.

Lung Infections and Old Age

Despite his history of illnesses and hospitalizations in the past decade, including a fight against prostrate cancer in 2001, Mandela's recent bout of lung infections could simply be a factor of his old age. During an interview with Scientific American, pulmonologist Steven E. Weinberger said that the body's defense mechanisms change with age, and immune system cells are less capable of making antibodies. It's called immunosenescence.

"One wonders if there are any structural changes in [Mandela's] lungs," Weinberger said. "For example, if he has any form of underlying lung disease, that will affect the lung's defenses and may make him more susceptible to infections. These kinds of structural changes are more common in older people."

Weinberger said that certain vaccinations are important to prevent lung infections - the annual influenza and a dose of the pneumococcal vaccine - as well as oral hygiene and avoiding smoking.

Many South Africans seem to share Kathrada's melancholy when it comes to their beloved leader's condition. When Kathrada saw Mandela, he told the AP that he experienced "an overwhelming feeling of sadness, and of course the unrealistic wish and prayer that he can be with us for longer and longer."