In June 2012 Angolan customs agents found more than they bargained for when conducting a routine check on containers shipped from China to the country's capital, Luanda.
While inspecting electronic speakers bound for local markets, the customs officials uncovered 1.4m packets of Coartem, a leading antimalarial drug produced by the Swiss pharmaceutical company Novartis. The amount was large enough to treat over half of Angola's annual malaria patients.
The catch was that the confiscated drugs were not genuine. They were counterfeit. This seizure turned out to be one of the largest of fake medicines in history, and shone a light on Africa's mounting struggle with phony pharmaceuticals - a problem which stretches well beyond antimalarial pills to products ranging from antiretrovirals to emergency contraceptives.
A unit of America's National Institutes of Health (NIH) collected surveys examining 2,634 malaria drug samples across 21 sub-Saharan African countries. Their 2012 findings were bleak.
Of those tested, over one-third "failed on the basis of chemical analysis" - meaning that they were either expired or of poor quality - and about 20% were found to be counterfeits.
Separately, Interpol and the World Health Organisation (WHO) say that anything between 30% and 60% of the continent's total drugs - both branded and generic - could be fake.
That comes at a high price. Around 100,000 deaths a year in Africa are linked to the counterfeit drug trade, according to the WHO. Globally, the London-based International Policy Network attributes 700,000 fatalities to bogus malaria and tuberculosis (TB) medicines every year.
The figures are alarming, but in truth the extent of the problem is almost impossible to measure, not least because no one agrees on how to define counterfeit and ill-made medicines. In addition, there is little consensus on what proportions of drugs are bogus, stolen or sidetracked.
But what is clear is that the proliferation of fake and substandard medicines is threatening advances made against some of Africa's most burdensome diseases, including HIV/AIDS, malaria and TB.
"Poor quality antimalarial drugs are very likely to jeopardise the unprecedented progress and investments in control and elimination of malaria made in the past decade," said Dr Joel Breman, a co-author of the NIH paper that focused on antimalarials.
Unscrupulous street merchants and unwitting pharmacies sell these phony drugs, which also pose a threat to the integrity of national health systems at large.
"When you have a lack of effective treatment, the patient in the long run will have a lack of trust in the national health system and in health professionals," argued Sabine Kopp, who heads the WHO's medicines quality assurance programme and anti-counterfeiting programme. This distrust deters patients from returning for future treatment, she added.
Most substandard and counterfeit drugs are believed to originate in Asia. A 2009 report by the UN Office on Drugs and Crime found that 45m courses of anti-malaria medication valued at $438m were shipped from India and China to West Africa.
Think-tanks like the International Policy Network say that China, which exported $1.5 billion worth of medical products to Africa between January and September 2012, plays a leading role in the distribution of medicines which, in some cases, have few or no active ingredients at all.
"China is the most important player globally when it comes to the counterfeiting industry," said Roger Bate, a visiting scholar at the American Enterprise Institute (AEI), a Washington, DC-based think-tank.
Participants range from criminal entities trading fraudulent products to legitimate manufacturers, which are failing to meet international standards.
Africa, with its porous borders, bribable officials, lax medical regulation, weak enforcement systems and desperate consumers, has proved a lucrative and easy dumping ground for these products. Fortunately, awareness is growing and responses are beginning to emerge.
The continent's mobile revolution is providing one mechanism for action. In 2001 only about 25m people in Africa had a mobile phone subscription. By last year that number had shot to around 650m.
A West African firm, mPedigree Network, has pioneered mobile authenticity checks to identify counterfeit drugs. A growing number of pharmaceutical companies looking to protect their sales and their patients are using this system.
A buyer simply scratches off a layer on a medication's packaging to reveal a unique code and then sends it as a free text message to verify the product's authenticity.
This May Guilin Pharmaceuticals and Watson Global Pharmaceuticals broke new ground by becoming the first Chinese drug companies to sign on to the mPedigree system.
Guilin is the manufacturer of Artesun, an antimalarial drug, which has received "prequalification" status from the WHO programme that authorises good affordable drugs for aid programmes. It plans to reach 10m patients in Nigeria, while Watson aims to reach a more modest 80,000 patients initially.
The buy-in of a Chinese company is an important development for mPedigree, which partners with more than two dozen mobile operators and handfuls of pharmaceutical companies across Africa and Asia.
"We haven't until now had a lot of cooperation from the Chinese manufacturers and we had been getting worried because you are not going to make a lot of progress if you are not getting them on board," said Bright Simons, the company's founder.
"Given how quickly China is building a market-share in the global South pharmaceutical trade, this could represent a seismic shift in the fake medicines situation. My view is that other Chinese groups will also now start to come to terms with the problem."
Other players are also operating in this space. For instance, Sproxil, a mobile phone-based start-up, partnered with telecoms giant Bharti Airtel in 2012 to bring its mobile drug authentication service into Airtel's 17 African countries free of charge to users.
But this is only one mechanism to fight counterfeit drugs. It needs to be paired with regulatory and legal responses if countries are to prevent the entry of fake medicines into supply chains at all. On this front, Rwanda is leading the pack.
A new report, co-authored by the AEI's Mr Bate, finds that the tiny east African country has all but eliminated fake tuberculosis drugs from its stocks. Of the study's 11 African nations, Rwanda was the only one whose samples showed no falsified products and few substandard ones. "Other countries are trying, but no one has done quite as well as Rwanda," Mr Bate said.
The main reasons behind Rwanda's success are the government's concrete legal and technical steps to ensure the quality of its drug distribution network. This includes banning private pharmacies from selling malaria and anti-tuberculosis drugs.
Bringing control of these two diseases into the publicly funded health system permits the government to closely monitor tendering processes with pharma suppliers.
"What Rwanda has tried to do is enforce its own laws, which is a rarity across the continent as a whole," Mr Bate explained. "A lot of countries still don't make counterfeiting a criminal offence, but even in African countries where the laws are in place they are usually not enforced."
Rwanda has also succeeded in coordinating its government agencies, including the Customs Services Department, the Bureau of Standards, the health ministry and the police force, enabling a swifter response to the distribution of illegal products.
Its success should be a shot in the arm for other African nations, but many are still struggling to clamp down on the problem. "In principle it's not difficult what Rwanda has done, but in practice most other countries just do not have this kind of coordination," Mr Bate argued.
Regional regulatory bodies such as the East African Community's Medicines Registration Harmonisation Project could ease the pressure on individual countries.
It was launched last year as part of an African Union programme that aims to synchronise the approval of good quality, safe medicines with stringent regulatory authorities as well as crafting national and regional medicines regulation. West Africa could follow, according to the World Bank.
"Regional harmonisation can help countries by bringing up the standards of operation in every participating national agency, freeing resources through division of labour and building regional systems for information exchange that allow regulators to identify threats earlier," explained Andreas Seiter, the World Bank's senior health specialist for pharmaceuticals.
Regional coordination and cooperation will face challenges. "The problem is the corrupt nature of certain authorities in some of these countries," Mr Bate argued, pointing to Kenya as "a shambles".
East Africa's economic powerhouse "is the largest and most important country in that region, but as a country as a whole it's not doing well in protecting its population against bogus medicines. I don't see how good the harmonisation will be unless Kenya gets its act together."
Reproducing Rwanda's success should be the goal of all governments, one that will be impossible to fake.