oestrids

Oestrids are a family of parasitic flies, the Oestridae, within the order Diptera. Also known as bot flies, they are obligate parasites during their larval stage, infecting a wide range of mammals, including livestock and, in some cases, humans. The group is divided into several subfamilies, notably Oestrinae (nasal and sinus parasites such as Oestrus ovis), Hypodermatinae (warble flies of cattle), and Cuterebrinae (cutaneous bot flies in rodents and other mammals).

Life cycle and biology

Adult females typically lay eggs in the environment or on vectors such as biting insects. In many species, larvae enter the host through skin or mucous membranes, or migrate to nasal passages, brain regions, or subcutaneous tissues, where they develop as internal parasites. After reaching a final instar, the larvae exit the host and pupate in the environment, from which adults emerge to reproduce. Adults generally do not feed. Some species, including Dermatobia hominis the human botfly, use a live vector to deliver larvae; eggs hatch on the vector and the larvae transfer to the mammalian host when the vector feeds.

Hosts and disease

Oestrid larvae cause myiasis, the infestation of living tissue by fly larvae. Products of infestation range from nasal and sinus disease in small ruminants and cattle to subcutaneous warbles in various mammals. In humans, oestrid infections are less common but can occur, with symptoms depending on the site of larval development. Diagnosis is typically based on clinical signs and the presence of larvae or characteristic lesions; treatment involves removal of larvae and management of the environment and host to prevent reinfestation.

Distribution and impact

Oestrids are found worldwide, with higher prevalence where suitable mammalian hosts and warm climates support their life cycles. They are of veterinary importance due to economic losses in livestock from reduced weight gain, tissue damage, and medical costs associated with infestation in some regions.