Myiasis is defined as the invasion of organs and tissues of humans or vertebrates by dipterous larvae, which then feed upon the living or dead tissues for some period of time (^{HALL; WALL, 1995}). Oestrus ovis Linnaeus, 1758, or the sheep bot fly, deposits its first instar in or near the nasal passages of small ruminants, and the larvae subsequently develop within the nasal fossae and cranial sinuses (^{HEATH; JOHNSTON, 2001}). The pathogenicity of O. ovis is believed to be the result of mechanical trauma induced by larval hooks and spines (^{DORCHIES et al., 2006}). The clinical manifestations of oestrosis may include long-lasting rhinitis and sinusitis, or the symptoms may have a clear-cut seasonal pattern (^{MARTINEZ et al., 1999}).

In Peru, O. ovis is a common parasite among sheep and goats (^{ZALDIVAR, 1991}). While it is believed that three species of bot fly can parasitize the nasal passages and sinuses of South American camelids (SACs), there is still a lack of information regarding the life cycle of O. ovis in these camelid species, given that no case reports on O. ovis in SACs exist in the literature (^{FOWLER, 1998}). The only published report of a bot fly in a SAC was a case of a nasopharyngeal bot-fly of deer (Cephenymia sp.) that was found in a dyspneic 9-month-old llama in Oregon, USA (^{MATTOON et al., 1997}). Here, we present a case of nasal myiasis in a llama (Lama glama) in Cuzco, Peru, caused by the parasite O. ovis.

A 1.8-year-old, 70 kg male llama that was living at the experimental station of the IVITA Veterinary Center, University San Marcos, in Marangani, Cuzco, Peru, began to develop respiratory symptoms. This llama belonged to a mixed herd of free-roaming sheep, llamas and alpacas from the Abra La Raya locality in Cuzco. This region has a cold climate, and is situated at approximately 3,700 m above sea level. The llama was sent to the clinic because it presented dyspnea, respiratory stridor, and bilateral mucous nasal discharge. Pneumonia was diagnosed, and the animal was treated with an antibiotic (oxytetracycline, 5 mg/kg intramuscularly) and anti-inflammatory therapy (dexamethasone, 0.05 mg/kg intramuscularly). However, the clinical signs lingered on and, four months later, the animal died suddenly.

At necropsy, the lungs revealed pulmonary hemorrhage and the cause of death was determined to be bilateral hemorrhagic pneumonia. Upon further inspection of the upper respiratory system, six intact dipterous larvae were discovered within both the nasal fossae and the cranial sinuses (Figure 1). All of the larvae were collected from the nasal cavity. Microscopic examination of the cephalopharyngeal skeleton and posterior spiracular plate was performed using the keys of ^{Papavero (1977)} and ^{Colwell (2006)}, and these larvae were confirmed to be O. ovis.

Figure 1.  Oestrus ovis in the cranial sinuses (in situ). Scale-bar: 2.00 cm. 

One larva was identified as a second-instar larva (L-II) and the other five larvae were identified as third-instar larvae (L-III). The second-instar larva was 1.6 cm long and 0.6 cm in diameter. The third-instar larvae had the following characteristics: cream color, 2.3-2.8 cm in length and 0.6-0.8 cm in diameter.

This case suggests that llamas are able to serve as accidental hosts for the O. ovis species of bot fly. The O. ovis larvae in this llama were able to complete their life stage development up to the third and final instar larval stage. This llama's clinical history of persistent pneumonia probably contributed towards establishing a state of relative immunosuppression. It is likely that these parasitic larvae were able to develop in the llama because of its compromised immunological state. Moreover, the llama lived in a mixed herd with sheep and had the opportunity of exposure from a definitive host. The clinical signs observed in this llama were similar to those experienced by sheep infested with O. ovis.

The sheep bot fly, O. ovis, is one of the most ubiquitous parasites of both the Old and the New World (^{HALL; WALL, 1995}). These flies can thrive in a wide range of environmental temperatures, and despite their specificity as parasites of sheep and goats, O. ovis has been reported in a variety of hosts (^{BIGGS et al., 1998}). Many reports have provided prevalence data for various regions, including both temperate and tropical areas (^{ABO-SHEHADA et al., 2000}; ^{CARACAPPA et al., 2000}; ^{DORCHIES et al., 2000}). In hot and dry climates, the nasal discharge caused by oestrosis can become caked with dust, making breathing very difficult (^{DORCHIES et al., 2006}).

Oestrosis is an important disease that has implications for communities' economies and for animal and human health (^{CARACAPPA et al., 2000}; ^{DORCHIES et al., 2000}; ^{COLWELL et al., 2006}). The magnitude of the clinical presentation of the disease is directly correlated with the number of larvae deposited. Light infestations in sheep comprising 15 or less larvae can, in fact, be well tolerated by the animal (^{COLWELL et al., 2006}). However, heavy infestations can have serious consequences, resulting in losses of meat, wool and milk production (^{DORCHIES et al., 2003}).

Although O. ovis is a common parasite in sheep and goats in areas around the globe, O. ovis has the potential to infest other types of ruminants. In Egypt, Old World camels can be infested with O. ovis (^{FEKRY et al., 1997}; ^{MORSY et al., 1991}). This fly also has been reported in wild sheep and goats, including the Siberian ibex (Capra ibex sibirica), argali (Ovis ammon), bighorn sheep (O. canadensis), Barbary sheep (Ammotragus lervia) and the European mouflon (O. orientalis musimon) (^{MORENO et al., 1999}).

In the present study, one llama was infected with O. ovis. This report documents the first known case of nasal myiasis in a llama by O. ovis in Peru.