"I left my husband behind to come and look after my sister because she was ill but then I got sick too," said Marita. "Our older children have to go and work in other people's fields to feed all of us."
The sisters, and the rest of their family, are paying the price for Malawi's decision to defy the West's pharmaceutical giants. Malawi took a stand against the purchase of expensive branded medicines produced by the big pharmaceutical companies, opting instead to buy generic HIV drugs approved by the World Health Organisation.
It was a brave decision: countries that insist on using only generic drugs get no money from the American funding programme Pepfar (President's emergency plan for Aids relief). Malawi decided it was better to forgo this funding and buy generics, than meet the conditions that came attached.
But as a result, Malawi can only provide a basic, three-drug cocktail, Triomune, to HIV-positive patients. About 20 per cent of the population is thought to have the virus, and the government has recently introduced a policy of providing free, generic anti-retrovirals (ARVs) to anyone who needs them.
Health workers are eager to sign up as many patients as possible for the treatment. But the help on offer is critically limited.
The generic drugs work well in standard cases, but they are not suitable for children, or for people with additional complications.
Anna needs more sophisticated drugs. Marita's case is worse. She would probably respond well to Triomune, but first needs to walk 10 miles to the nearest hospital, Mulanje Mission, for assessment.
"These women have to walk here each month to be assessed for ARVs and they are just too weak to make the journey," Ellen Gama, the local community nurse, said. "We don't have the capacity to ferry patients around. We need more health centres near them, but we have no staff for that."
Malawi, a country of 12 million people, has 2,000 nurses and 100 doctors working in all its public hospitals - less than a third of the number there should be.
Nurses, who earn just 25,000 kwacha (£112) a month, are lured away from Malawi by offers of lucrative jobs within the NHS. The brightest doctors are offered research posts by major American universities, who pay far more than the Malawi state salary of between £121 and £145.
"The staffing shortage, more than anything, is stopping Malawi providing ARVs to the people who need it," Mary Fitzgerald, a doctor with Médecins Sans Frontières, in Blantyre, said. "There are now various schemes to top up doctors' salaries, but we need to persuade lower-level health workers like nurses and clinical officers to stay too." There are about 170,000 people in Malawi who are in need of ARVs.
Problems of funding and staffing mean that only 23,000 of them are receiving medication. As a result of the staff shortage, the only health worker that visits Anna and Marita regularly is Limi Lemano, a "home base care" volunteer.
Limi never made it to secondary school, but he has attended a three-day workshop at the local hospital and is now allowed to hand out aspirins and wound dressings to people in his village. In theory, his patients are then meant to go to hospital for more treatment. In reality, the asprin is the only medication they get. So each time Marita and Anna get sick, they stay shivering inside their mud hut while Anna's 15-year-old son, Robert, and his younger sister walk for seven hours to find work in neighbouring Mozambique.
And soon, Malawi's problems may get worse. Until now, India has produced most of the generic Aids drugs by ignoring international patent law and simply copying existing formulas. But earlier this year, the Indian parliament agreed to comply with the World Trade Organisation's intellectual property laws and make it illegal to copy patented drugs.
The move will eventually cut off the supply of cheap drugs to countries that rely on them the most. At the moment a course of generic Triomune costs Malawi $16 (£9) a month per patient. European and American drug companies provide the same treatment for more than four times that.
In Malawi, the fight against Aids is getting urgent. The rains failed this year and there is a severe shortage of food in rural areas. Aids patients who had managed to remain healthy through good nutrition have already begun to starve to death. Unless Malawi can get more money for ARVs, and persuade doctors and nurses to stay in the country and treat its patients, the battle may be over too soon.
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