This would be very odd, but he's from Kenya, and so would have been exposed many times to Bilharzia. In Malawi, fairly nearby, all volunteers were tested with a new test back in 1992 or 1993 and more than 50% tested positive. Just one swim in the lake could do it. It can be debilitating. A volunteer from another country at the time was paralyzed when it went into her spine. Typhoid is also endemic to East Africa and we all had to have the very painful vaccine for it. I wouldn't be surprised if he's also had malaria a few times. I had something very much like it when I was travelling in Zanzibar and Pemba, recurrent high fevers, etc., though my blood slide back in Malawi tested negative for it (I was on Mefloquine).