The Sunday Herald/Concern Worldwide Christmas Appeal for East Africa.

They poured into the city from the countryside to escape the impacts of climate change and extreme poverty. They found a nightmare they could hardly have imagined.

She lay slumped in the mud of the alleyway.

The looks of the bystanders gathered around the young woman told their own story of what had happened. Each was a cameo face of fear, resignation, shock and indifference.

A young man had stabbed her, they said. No-one for sure knew the reason why.

Maybe the attacker had wanted her old, near-useless mobile phone. Then again she was found barefoot, so perhaps he'd knifed her before making off with her cheap flip-flop sandals.

It's possible, too, she was carrying a little money, certainly not much here in a place where people survive on less than 50 pence a day.

Of course, her attacker might just have stabbed her for the hell of it, high on booze and dope, oblivious to what he was doing.

She was a woman after all, alone, vulnerable, easy prey. As many as 30 stabbings weekly happen here in this neighbourhood spread across no more than a mile or two, and that before the shootings and muggings.

Almost always the victims are women. Young or old, it matters little to the thieves and thugs.

If it's not robbery then it's rape, often in broad daylight. The grinding poverty and paralysing fear that has already violated the lives of the passers-by renders them incapable of intervention.

How does one begin to describe the lives endured by women who live here in the slums of Korogocho and Mathare?

For even by Africa's own terrible standards these shanty towns on the outskirts of the Kenyan capital, Nairobi, are among the most volatile and squalid on the continent.

Korogocho is the last stop, you can't fall any further short of being totally destitute or dead, one local aid worker tells me, as we drive out from the city centre towards the slum.

I wanted to find out for myself what it's like for the women here who lead a life of fear, unremitting toil, and who worry constantly over the disease and hunger that stalks their children.

In the back alleyways of both slums I was to meet four such women, young and not so young. What follows is a glimpse into their hopes, fears and above all fight for survival in the heart of this human abyss.

The rainy season downpours were clattering on the corrugated tin rooftops as we wove our way through the narrow passageways of Grogan A District in Korogocho. So crammed together are the huts here that the alleyways are no more than the width of a coffin, and for those entombed in these dank confines that's precisely what neighbourhoods like this feel like – coffins.

Such is the claustrophobic proximity of these garbage-strewn corridors, that you can easily touch the ramshackle walls on either side with outstretched arms. For the estimated two million slum dwellers of Nairobi, this is where the majority, especially women, will spend almost all their lives.

In the searing heat of the summer the stench is overpowering, while now at the height of the rainy season the open sewers overflow into people's homes.

This has always been a dangerous and violent place too, and it's only with an escort of local youths as security against attack that we as outsiders are able to make our way to the home of Purity Atieno, a 21-year-old mother of three young sons.

"Believe me when I say that the criminals who roam here in Grogan are not intimidated by us, it's simply that we have put the word out and made an understanding of sorts for your visit," one of our young minders points out as we enter this most notorious of slum districts.

Walking here is like navigating a minefield of filth. After a while you give up caring what you may be stepping on, human faeces, raw sewage and dead rats. On more than one occasion, though, I catch a glimpse of the live vermin, which locals tell me have been known to grow as big as cats.

This is nothing, however, compared to the gigantic illegal Dandora dump site that sits adjacent to Korogocho and from which many slum dwellers depend for their survival.

Dandora is the one and only dumping site for the waste of Nairobi's entire four million inhabitants.

Chemical, hospital, industrial, agricultural and domestic waste, it's all thrown here on this hillside and left unprocessed. Such is the pressure for space that the slum dwellers of Korogocho have no choice but to burn some of the garbage, the resulting toxic fumes contaminating the air 24 hours a day and crippling the health of almost a million of these impoverished people.

According to one United Nations report, these effects include irreversible damage to the immune, nervous and reproductive systems. It also causes respiratory, gastro-intestinal, skin diseases and different kinds of cancers. In one test carried out on Korogocho slum children more than half had blood abnormalities that signalled heavy-metal poisoning exceeding accepted international levels.

The dump is one of the worst places you can imagine, and the people who are there can be very threatening, Purity Atieno tells me, cradling her newborn son Migel Elijah in her arms.

We are inside her threadbare hut in the heart of Grogan district in Korogocho and from here, every day before dawn, she rises to make her way to the Dandora dump site where she will rake among the food waste, hospital waste, used syringes and even the bodies of murder victims that can be found there.

This she does for a few plastic bottles, which she sells to make what she calls her daily bread. Tough and dangerous as such work is, it is preferable, Purity says, to the terrible time when because of the need to feed her children she admits to having sold her body to men. Tall, lithe, with strong aquiline facial features, she smiles when talking about how she braids hair from which she makes a little extra money along with the pittance earned from the dumpsite scavenging.

"The thing I need most is food, and the thing I fear most are the rapists, who come in the night as I live alone," she confesses.

Born in Korogocho, Purity is about to spend her 22nd Christmas in the slum. What would Christmas Day mean for her and her sons, I asked?

"I don't know whether we will be happy this Christmas or not, it all depends on whether we can eat that day," she replies matter-of-factly. As I rose to leave that afternoon I couldn't help noticing a tiny kitten tucked away in the corner of the hut that I assumed, wrongly, was her son's pet.

"Not really a pet, we need it for the rats, they are everywhere at night, but the smell of the cat helps keep them away," she corrects me.

For those of us used to the comparative comforts of our own developed world lifestyle, it's hard to fully comprehend the energy and courage it takes for those like Purity Atieno just to get through another day. But among the women of the slums there is strength of character born out of extreme hardship and adversity.

Elizabeth Aoko and her husband came to Nairobi some years ago from rural northern Kenya in search of work and a better life.

Like many slum dwellers who originated in the countryside, the impact of climate change and other economic factors left them unable to make a living and so they headed for Nairobi and what they hoped was a new beginning.

Instead, they found themselves in Korogocho where today she ekes out a living by selling a few vegetables and he as a casual labourer.

"Life here is simply about surviving. When our relatives come from the north of Kenya to visit us, it's embarrassing for us when they see the way we live here," Elizabeth says.

At 29, she admits to being angry that she and her family are forced to live this way, and frustrated when she sees other people living well. But her greatest fear, she says, is that her children might be struck down by disease.

"Everyone in Korogocho has similar problems so we share when we can, that means if I need salt my neighbour gives me some, this is the only way to cope here," she explains as a few tiny chicks skit along the dirt floor at our feet.

But in the past Elizabeth has helped her neighbours out by offering much more than with the little foodstuff she has. Following the death some years ago of some friends, she adopted the deceased parents' two children, bringing them into her own struggling household alongside her own four daughters and sons. Why take on board such an additional responsibility I asked her?

"I took them because I could not bear to see them left alone, and though we have little we can always find a way to share," she says adamantly.

Huge as Korogocho slum is, it is not the biggest in Nairobi. That dubious distinction goes to Kibera with the second-largest being a place called Mathare. It was in the oldest of Mathare's slums that I met two women of a different generation from that of Purity Atieno and Elizabeth Aoko.

According to estimates, the series of slums that make up Mathare itself is home to anywhere up to 700,000 people crammed into an area two miles long by one mile wide. In recent years its population has grown following controversial presidential elections and the subsequent violence that displaced thousands of Kenyans into Nairobi's slums.

Mathare is also home to the infamous Mungiki a secretive criminal gang-cum-quasi-religious sect whose members cut out their enemies' navels and worship a leader who says he came from a ball of shining stars.

Here in Mathare organised crime is rife, and many of the slum landlords who own the property here are inextricably connected with such organisations.

Malisela Mbithe, 58, came here in 1987 with two daughters who both subsequently died, one following bouts of pneumonia and malaria, the other after a mental breakdown. Both were teenagers, only 16 and 18 years old.

Today, Malisela lives in Mathare with her grandchildren and two other orphans that she took in. Like all the women of the slums, hers is a precarious existence.

In the days that I met her she herself was recovering from a bout of malaria that had curtailed her meagre work selling vegetables and tea by the roadside outside Mathare.

The little income she makes barely covers the cost of her rent for the tumbledown corrugated and wooden shack in the narrowest of alleyways in which she lives with the four children. For this she has to pay 1600 Kenyan shillings a month.

"Miss one payment and the door is pulled off by the landlord's men leaving you to the thieves at night," she tells me, adding that this is standard practice before the eviction that follows.

Of the lawlessness that is rife in Mathare, Malisela says she herself has not been a victim, as she possesses nothing for anyone to steal.

Like the young women of Korogocho, for Malisela Christmas is just another day that depends on income though "having meat to eat would make it special", she says.

In better times with a little money she and the children would have travelled up country to visit relatives but today that is impossible, she confesses.

"I'm weak from the malaria, but need to keep working to eat, to make sure the children can get to school," she explains, proud that they have at least managed to keep up some of their studies in Mathare.

Time and again during my visits to both Korogocho and Mathare, it was this selflessness and willingness to share that struck me most about these women of the slums.

Perhaps no-one epitomised this more than Ndimba Nguli Muli.

At an estimated 76 years old – no-one seems fully sure of her age – she lives alone in Mathare, her life in the slums made all the more terrifying by the blindness that resulted during the birth of one of her eight children, all of whom bar one subsequently died.

For almost all her life, Ndimba has been on the receiving end of all that Mathare and Nairobi's other slums could throw at her.

She had a son shot dead in street violence, suffered from epilepsy, and last April while begging by the roadside she was hit by a car and her right leg badly injured.

At night she lies awake in the filthy wooden box that passes for her home listening to the gunshots that ring out as rival gangs clash in the alleyways.

Totally dependent on the help of her neighbours, she tells me that "only God knows if I will eat today", when I ask how she survives.

Unbelievably as we speak, she never tires of cracking jokes, undaunted by her blindness and the terrible hand life has played her.

Given a single wish, what, more than anything, would she like in life right now, I ask her?

Almost instantly she leans forward before grabbing the arm of my Kenyan guide and interpreter.

"Give me this man," Ndimba announces, a teasing and mischievous grin breaking out on her face.

Right now 13 million people in East Africa are facing severe food shortages. In the slums of Nairobi alone, food prices have risen by an astonishing 200 per cent, pushing people already living on a knife edge further into poverty. Concern Worldwide is on the ground providing immediate assistance as well as helping people to build a future.

- £6 can help feed two children for one month.

- £35 can help treat one severely malnourished child.

- £116 can help provide vital training to a community health worker in the slums.

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