South Africa and Nigeria are embroiled in a diplomatic spat after the authorities at Johannesburg airport deported 125 Nigerians, alleging their yellow fever vaccination certificates were fakes - the latest twist in a long-standing rivalry between Africa’s two biggest economies.Nigeria has responded with undisguised tit-for-tat deportations of 84 South Africans in the past two days, according to a senior official at the State Security Service who could not be named.