As far as I can know from my own knowledge on the subject, I don't think there was any real problem of European diseases causing pandemics in Africa due to a lack of immunity. It was, if I recall correctly, more difficult for European colonists who were less adapted to African diseases. Napoleon's campaign to try and seize Egypt for the French in the late 18th - early 19th century was majorly affected by disease in North Africa which demoralized and weakened his army significantly. The difference between the Americas and Africa is of course that America had been completely isolated from diseases in the old world. This was not the case for Africa.

Africa had pretty much always been in contact with Europe through things like trade or early empires like the Roman Empire, which controlled Northern Africa for a great deal of time. Disease therefore wasn't isolated from Africa. The build up to colonization had been a lot more gradual than with the colonization of the Americas. Places such as Sao Tome island, ruled by Portugal, had been colonized prior to Columbus even setting foot in the Caribbean.

Africans were probably more immune to diseases and illnesses than the Europeans were, this was one of the contributing factors that made the slave trade initially so profitable over using peasants from Europe. This is not to say disease didn't pick up during the Scramble for Africa, i'm sure it did, especially in places like the Belgian Congo, but I would imagine that would be down to poor governance rather than a lack of resistance to disease by locals, which is what got the Native Americans. I know that some diseases were introduced to East Africa during the Arab settlement of the eastern coast but even these were evidently nowhere near as damaging as disease was to the Native Americans.

In summary, I cannot think of any obvious instances where the African population was heavily reduced due to a lack of resistance to diseases brought by Europe. Primarily because Africa had pretty much always had contact with Europe and the rest of the old world and the two continents regularly traded, fought with one and other or conquered their territories. Europeans were often affected by African diseases more than Africans were by European disease. However, disease was commonplace in Africa and already had been for many centuries, this was intensified during the European period as urbanization increased and populations became more interconnected. I don't claim to be a genius on the subject but from what I know, I cannot think of any plagues or major epidemics brought to Africa through the scramble for Africa which were not already in contact with Africans.