THESIS SUBMITTED IN FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY OF SOKOINE UNIVERSITY OF AGRICULTURE. MOROGORO, TANZANIA.A study on GED was conducted in the Mikumi - Selous ecosystem with an overall objective of finding the cause and predisposing factors. Giraffes were examined for change in conformation, discharges, and lesions on the pinna. Samples were collected from immobilized giraffes. Water and browsing materials in giraffe habitat were collected for micro-organisms isolation. Tick and oxpecker surveys were conducted. GED overall magnitude was 11.7% (dry) and 11.1% (wet) seasons (1999 to 2006).3.1% (dry) and 8.1% (wet) seasons (2007 to March 2010). Matambwe in Selous Game Reserve 1.2% (dry) 2.4% (wet), MINAPA 0.8% (dry) and 1.2% (wet) seasons (2007 to March 2010). The difference mean sick giraffe examined in each ecozone seasonally was not statistically significant (P > 0.05). Immobilized giraffes revealed thickening of the ridges of antihelix, and distal part of the scapha, superficial erosion, pus, and foul smelling of the pinna concave surface. GED harboured environmental bacteria Pseudomonas auregenosa and Bacillus firmus. Rhipicephalus appendiculatus and Amblyoma variegutum were common ticks associated with giraffes. Ticks and oxpeckers played no role on GED occurrence. Histologically GED biopsies had epidermal nematode larvae and interepidennal necrosis. Molecular investigation concluded the nematode was a Spirurid. GED is dermatitis caused by Spirurid nematode. The DNA sequence lies between Onchocerca and Dirofilaria species which are parasitic to human and animals. It is therefore a species that is new and specific to this ecosystem. Furthermore, possibly it is a species that have evolved from older, non pathogenic and common environmental agent. It is concluded that for the first time this work has been able to demonstrate and isolate a Spirurid nematode which is the primary cause for GED with bacteria and fungi working together. The mechanism by which the nematodes and bacteria cause the damage to the pinna is of interest. Also the trend of the disease magnitude was downwards. It is recommended GED be known as Giraffe Pinna Dermatitis. Mechanisms by which the nematodes cause lesions and role of vectors need further study. Establishment of national nematode bank, reference archive with identification keys, micro weather stations, electronic geomaps, and monitoring programme.