Myiasis: Hypodermatidae and Gasterophilidae Infestations

Understanding Myiasis: Larval Infestations

General Overview of Myiasis

Larvae develop and, upon reaching the third stage, can be released through a sneeze. These infestations can cause significant economic losses in livestock. At the human level, sanitary issues often occur in people in contact with cattle. Larvae released onto the eyes can cause external ocular myiasis. While often benign, it is very annoying because the larvae produce irritation at the level of the conjunctiva and cornea.

Hypodermatidae Family: Cattle Grubs

The Hypodermatidae family includes various Hypoderma genera, some with significant health implications, such as Hypoderma bovis (major cattle grub) and Hypoderma lineatum (minor cattle grub).

Life Cycle of Hypodermatidae

Adults, resembling bumblebees, are primarily found in spring during warmer periods. They lay eggs, which are firmly attached to the hair of cattle. Multiple eggs can be laid on a single hair, or individually. From these eggs, first-stage larvae hatch. These larvae penetrate the skin and migrate to different parts of the dorsal median area. Here, they evolve into second and third-stage larvae, producing tumoral injuries commonly known as "warbles" or "mud."

These third-stage larvae must exit the host. They do so by opening a skin ulcer with a central pore, through which they emerge and fall to the soil. Once in the soil, they burrow and pupate, with adults emerging later. The entire life cycle typically lasts about a year.

Health Significance of Hypodermatidae

In humans, these larvae can cause simple cutaneous myiasis, often presenting as a tumoral lesion on the neck and trunk. While generally of minor significance, this myiasis can migrate and, in rare cases, penetrate the eyeball, potentially leading to ophthalmomyiasis and even loss of the eye.

Gasterophilidae Family: Horse Bot Flies

The Gasterophilidae family adults also resemble small bumblebees and are common in warm weather. Their eggs are deposited and firmly attached to the hair, but in this case, they are found in areas where the horse (the most common host) can reach with its mouth or forelegs.

Life Cycle of Gasterophilidae

When a horse licks or grooms itself, the humidity and temperature of its tongue stimulate the eggs to hatch. The first-stage larvae are then deglutinated and pass through the esophagus to the stomach or intestine. There, they attach to the mucosa with the aid of anterior hooks, and subsequently develop into second and third-stage larvae. This entire development occurs within the host for almost a year. The mature larvae must exit the host, which they do via the feces. Once outside, they form pupae, which burrow into the soil, and adults emerge in the spring.

Health Significance of Gasterophilidae

In horses, these larvae primarily cause gastrointestinal myiasis. In humans, the larvae can penetrate the skin and begin to migrate through the dermis, seeking a suitable location. This migration leads to a condition known as creeping myiasis (larva migrans).

Diagnosis, Treatment, and Prevention of Myiasis

Diagnosis

Myiasis is typically diagnosed based on characteristic symptoms and the detection of the larvae's presence.

Treatment

The primary treatment involves the mechanical removal of the larvae.

Prevention

Prevention strategies include the slaughter of severely affected or sick animals to control the spread of infestation.