Lagos, Nigeria (CNN) As denials go, it was extraordinary and more than a little surreal.

The sitting president of Africa's largest democracy was forced to refute repeated claims that he had died and a clone was now running his office.

"This is the real me," said Nigeria's President Muhammadu Buhari, dismissing the allegation as "ignorant rumors" after a period of ill health. For the avoidance of any doubt, the denial is pinned to his official Twitter page

Welcome to the Nigerian election season, where disinformation and propaganda are nothing new. But in the lead-up to the 2019 presidential vote, now scheduled for Saturday, fake news "has been on steroids," says Lolade Nwanze, journalist and head of digital operations for the Guardian Nigeria newspaper.

In this context, she's talking about fake news -- stories that are either entirely made up or shared out of context.

Bankole Wellington, a pop star-turned-politician popularly known as Banky W , says he was the victim of a false claim on Twitter that he had received a bribe.

"It was completely false, no proof just a random tweet and in 10 minutes, we had a thousand retweets of people saying 'yes! I knew he was corrupt!' ... Nobody is looking for proof, it's not about what's true anymore," he told CNN.

Those close to the political parties have also been known to use fake news to tout their candidate's achievements and to score political points.

A close aide to President Buhari has been called out repeatedly on Twitter for sharing false information on her verified account.

Lauretta Onochie, who is a special assistant on social media to President Buhari, was forced to issue an apology after claiming that President Buhari built a new road that was actually in Rwanda

"My big mistake, apologies to all, friends and wailers alike. It won't happen again," she wrote at the time

However, months later, Onochie posted a tweet accusing opposition leader Atiku Abubakar of sharing food and money during one of his campaign rallies. Onochie posted an image of food packs with money attached to them, saying: "Keep them in poverty, then give them handouts. Atiku in Sokoto yesterday."

KEEP THEM IN POVERTY, THEN GIVE THEM HANDOUTS- ATIKU in Sokoto yesterday pic.twitter.com/JumaW5vi4A — Lauretta Onochie (@Laurestar) December 4, 2018

The claims were investigated by a coalition of journalists, including AFP and other Nigerian media, who found the image Onochie posted was from an earlier charity event , Nwanze says.

"She's notorious. It's the same format for all of them: half lies, half-truths. We debunk it, and she just doesn't care and moves onto the next one. She's quite consistent."

Onochie told CNN she has never knowingly posted fake news and that she has apologized for her error.

"The story I posted was true," she said. "It's the images that was the issue. I pulled it down and I have apologized."

"I have never deliberately posted fake news and I never will," she added.

Nwanze is part of a team of journalists from 15 media houses who joined forces to stamp out fake news.

The initiative, called CrossCheck Nigeria , works as part of a coalition with the International Center for Investigative Reporting.

It has a team of around 50 journalists who share allegations of fake news and try to sort out fact from fiction.

"Essentially, what we do is we identify claims and posts that we suppose are fake, and then we investigate them, then we go ahead and publish what the truth is," Nwanze says.

Some stories are easier to verify than others. For example, a member of the CrossCheck team found an account linked to the opposition People's Democratic Party (PDP) on Facebook had posted an image of US President Donald Trump, appearing to endorse PDP leader Abubakar Atiku.

A simple reverse image search on Google showed that the image had first appeared during the 2016 US presidential elections campaign.

CrossCheck swiftly published a rebuttal on their website and their social media sites. The team has also seen patterns emerge during the election cycle.

"There are some handles and some pages on Facebook that are really notorious," Nwanze says.

"One of them puts out a story, the same story is replicated in like three or four other pages, and that's how they just widen their reach."

Social media platforms such as Facebook and Twitter have faced criticism over the proliferation of fake news on their sites.

However, they say they are working hard to stem the tide of false information.

Facebook said in a statement to CNN that it is always monitoring and taking action against fake accounts and that it continues to invest heavily in people and technology to prevent abuse. The social media platform acknowledges it can always do more.

Twitter, for its part, says it is working closely with Nigeria's Electoral Commission to make reporting problem accounts easier and that it prioritizes the "health of public conversation during elections cycles."

"We employ purpose-built technology to surface relevant content first and proactively tackle the malicious spread of disinformation at scale," it said in a statement.

On sites like Twitter, where users have named accounts, handles that spread fake news can be traced and shut down.

But on WhatsApp, the messaging service that's ubiquitous in Africa, it is particularly challenging to establish the source of false information because of the platform's end-to-end encryption.

An eight-year-old CNN report about weapons being smuggled into Nigeria during the elections, filmed in the lead-up to the 2011 elections, has been shared recently on WhatsApp as if it was a current story.

The report centered on a massive hau l of illegally smuggled weapons discovered at a Nigerian port during what turned out to be one of the most violent elections in the country's history.

CNN has seen WhatsApp messages that showed how the report was passed around as if it related to the 2019 elections.

A spokesperson for WhatsApp told CNN that the encrypted nature of the messaging service means that the company does not have access to its contents.

However, it said it had built a "sophisticated machine learning system," that helps it to detect abusive behavior and ban suspicious accounts.

"We remove over two million accounts per month for bulk or automated behavior. We are constantly advancing our anti-abuse operations to keep our platform safe," it said in an emailed statement.

WhatsApp, which is owned by Facebook, has also taken out adverts on radio and newspapers in Nigeria ahead of the elections, encouraging people to "share joy, not rumors."

The motivation of those who reshared the old CNN report isn't known. But in Africa, elections can often be a matter of life and death. In 2007, more than 1,000 people were killed and hundreds of thousands displaced during Kenya's worst electoral violence.

The dissemination of false information -- in particular about the spread of weapons -- could have deadly consequences.

That's why initiatives like CrossCheck are so important. But despite its best efforts, Nwanze is the first to admit its work is a "drop in the ocean" in the effort to counter those determined to spread false stories.

"It's just really annoying because these people seem to be working round the clock," Nwanze says.

In any case, there seems to be little appetite for truth among those who peddle false information. When CrossCheck's volunteers have established a story as fake, they contact the author and encourage them to publish a new, verified version instead.

Most don't.