Nairobi sheep disease

Definition

A tick-borne viral hemorrhagic disease of sheep and goats caused by Nairobi sheep disease orthonairovirus (family Nairoviridae, order Bunyavirales), transmitted primarily by ixodid ticks including Rhipicephalus appendiculatus and Amblyomma variegatum. Characterized by acute fever, gastroenteritis, abortion in pregnant ewes, and high mortality in naive populations; endemic to East Africa with historical range extending to India (where a related strain was termed Ganjam virus).

Etymology

Named for Nairobi, Kenya, where the disease was first described in sheep during the early 20th century.

Example

In the East African highlands, Rhipicephalus appendiculatus ticks transmit Nairobi sheep disease virus to small ruminants during peak tick activity following rains, causing flock mortality exceeding 90% in susceptible imported breeds.

Synonyms

• Nairobi disease
• NSD
• Ganjam virus disease

Related Terms

• orthonairovirus
• Nairoviridae
• Bunyavirales
• Rhipicephalus appendiculatus
• Amblyomma variegatum
• tick-borne disease
• viral hemorrhagic fever
• Crimean-Congo hemorrhagic fever

Usage Notes

The term refers specifically to the disease syndrome in sheep and goats, not the virus itself (formally Nairobi sheep disease orthonairovirus or NSDV). 'Ganjam virus' historically described an Indian variant now considered the same species. Differential diagnosis includes Rift Valley fever and heartwater; confirmation requires RT-PCR or serology. Control relies on acaricide management of vector tick populations rather than vaccines, which remain experimental.