The families of the schoolgirls kidnapped by Boko Haram in Chibok, Nigeria, are struggling for survival as the two year anniversary of the abduction looms.

Eighteen parents of the kidnapped girls have died since the attack on 14 April, 2015, when 275 girls – mostly Christians – were taken from their school.

Almost 50 managed to escape, but it is believed 219 remain in captivity.

According to persecution charity Open Doors, the families of those girls still missing are seriously struggling to support themselves, and many are suffering from severe health problems linked to their trauma.

"I am carrying my wife to the hospital and they said she has high blood pressure..." said the father of one of the abducted girls. "Sometimes they (the hospital staff) don't see sickness, they will say, 'It is the thinking within your family'."

He said his remaining daughters are also suffering. When one of his daughters "hears something, she shakes, fearing that Boko Haram will come and abduct her like her sister," he said.

Though many fled in the aftermath of the April 2015 attack, some families have now returned to Chibok. However, schools have not reopened since the kidnapping, and so the local children have been out of education for two years. The town's markets have also been closed since the attack.

Open Doors has been working with local churches and partners to provide food, healthcare and counselling for those affected.

"We are counselled, we are advised, we are comforted. I really liked that," said Pastor Ayuba, whose daughter Amina was among the girls abducted.

"When I went back [home], I tried to pass the knowledge to my church. I organised some people and then began to teach them... They really wanted it."

Boko Haram, an Islamist militant group whose name translates as 'Western education is forbidden', has abducted hundreds of women and girls since its uprising in 2009.

Several weeks after the Chibok abduction, militants released footage of 136 of the schoolgirls purporting to show them having converted to Islam. The girls were shown wearing hijabs and reciting the Qur'an.

Some reports suggest that at least some of the girls have been brainwashed by their captors, and have carried out murders on behalf of the group.