What is Botfly?

The term “bot fly” refers to a type of fly from the Oestridae family. To reproduce, these flies depend on a process known as myiasis, which involves infesting a host’s skin to feed their larvae. If you’re infested by a bot fly, the issue usually resolves on its own within six weeks. During this time, the bot fly matures and leaves the host’s body on its own. However, having a bot fly larvae in your skin can be uncomfortable, and you might prefer to have it removed.

What Causes Botfly?

The types of flies that most commonly cause an infection known as myiasis in humans are the Dermatobia hominis (also known as the human botfly) and Cordylobia species. Dermatobia hominis is originally from the tropical regions of Central and South America. On the other hand, Cordylobia species, also known as the tumbu fly, are found in tropical Africa.

About 40 types of Cuterebra species, known as the rodent bot, are found in North America, but it’s rare for these to infect humans. Over the past 70 years in the United States and Canada, there have been fewer than 65 cases of myiasis caused by local bot fly species.

Risk Factors and Frequency for Botfly

Bot fly infections can affect anyone, no matter their gender, age, or genetic background. Most of the cases in the U.S. involve people returning from trips to Central and South America. We don’t have reliable global data on this disease, partly because it often goes unreported. This is because bot fly infections often resolve on their own, and there are many effective treatments available that people can apply at home. However, there is some evidence to suggest that cases of bot fly infections are increasing worldwide. This increase might be linked to climate change, and if that’s the case, then we can probably expect to see the rate of these infections continue to increase.

Signs and Symptoms of Botfly

Bot fly myiasis, an infection caused by fly larvae, can be hard to diagnose. When trying to identify it, one of the most important pieces of information is the patient’s recent travel history. Doctors should ask if the patient has recently visited areas like Central or South America or the African tropics, where this condition is most common.

The patient’s activities during their travels can also provide clues. For example, things like hiking and spending time outdoors can increase the risk of exposure to the flies that cause bot fly myiasis. Contact with mosquitoes, ticks, and other flying insects is another important detail to highlight.

Patients typically only report problems in the area where the infection has occurred. They might describe a slowly-growing lump, accompanied by swelling, which usually shows up a week after they’ve been bitten by an insect. The affected skin may become itchy and slightly painful, and patients may sometimes feel like something is moving beneath their skin.

Usually, patients don’t have a fever and their lymph nodes aren’t swollen. During a physical exam, the doctor might see a red bump on the skin, around 1-3 cm in size, with a central opening. Applying pressure to the bump could lead to a fluid possibly mixed with blood, coming out of the opening.

Testing for Botfly

Diagnosing bot fly myiasis, an infection caused by a type of fly larva, often involves using ultrasound. This imaging tool can help the doctor identify a brighter, or ‘hyperechoic’, mass just beneath the surface of the skin that blocks, or ‘casts a shadow’ on, the deeper structures underneath it.

Additionally, a complete blood count test may be conducted. This test can show an increase in two types of white blood cells: leukocytes, which are involved in fighting off infections, and eosinophils, which are primarily responsible for tackling parasitic infections such as the bot fly larva.

Despite these symptoms, the levels of erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) are usually normal. The ESR test checks for inflammation in your body, and the CRP test is a type of blood test that measures the amount of a protein called C-reactive protein, which is produced by your liver in response to inflammation.

Treatment Options for Botfly

In most cases, removing bot fly larvae, small worm-like parasites, doesn’t require surgery. Doctors typically recommend surgical removal only when the larvae are too large or difficult to extract, or when the eye, the area surrounding the eye (orbit), or scalp is affected. This is especially important when it comes to infections in children.

Several non-surgical methods exist for the removal of bot fly larvae. One approach is to block the central opening of the larva’s breathing apparatus, which can suffocate it. Alternatively, the larva can be extracted after it’s been numbed with lidocaine, a local anesthetic. Using a small surgical tool, known as a 5mm punch, for extraction is another possibility. The best initial step, however, is what’s known as hydraulic expulsion. This involves injecting lidocaine into the affected area, forcing the larva out. This way, the chances of accidentally cutting into the larva and causing a secondary infection are reduced.

Directly pulling out the bot fly larva is usually not recommended, as the larva has small, sharp spine-like structures (spicules) that help it anchor onto the host tissue. Trying to remove it directly could result in the larva tearing and potentially causing an infection.

There are also some home remedies that have been used effectively, such as smearing substances like petroleum jelly, paraffin oil, pork fat products, or other thick gels over the larva to suffocate it. However, these are not always the preferred methods, as removing a dead larva can be tricky because of the spines on its abdomen. Devices designed to extract snake venom have also been used successfully in removing larvae.

In some cases, if the patient does not wish to have the larva removed, doctors may recommend a watch-and-wait approach, under which they monitor the patient and implement treatment strategies only if necessary.

Bot fly myiasis, an infection by bot fly larvae, is not a common condition in the United States. This can lead to it being mistakenly identified as other, more typical skin conditions. Someone might have been given a treatment by another doctor, but there’s no improvement on their skin condition. The conditions that might look similar and should be considered are:

Sebaceous cyst (a small bump appearing under the skin)
Cellulitis (a bacterial skin infection)
Folliculitis (an inflammation in one or more hair follicles)
Abscess (a pocket of pus that forms within body tissues)
Foreign body (when an object is stuck in the skin)
Atopic dermatitis (a type of eczema)

The infection caused by the Dermatobia hominis bot fly can look a lot like an infectious boil, as both can cause red changes in the skin with a centre that looks like it contains pus.

What to expect with Botfly

Issues from botfly infections often get better on their own without any medical treatment. The severity of the problem largely depends on the area of the body the botfly has infested. Further complications will be discussed below.

Possible Complications When Diagnosed with Botfly

In some cases, removing the larva piece by piece can lead to secondary infections. This usually happens when the larva is removed at home with tweezers. Particularly in children, if the larva is located on the scalp, there could be a fatal risk of the brain becoming infested.

Key Risks:

Secondary infections from removing the larva in pieces
Risks associated with home removal of the larva using tweezers
Potential life-threatening brain infestation in children with scalp involvement

Preventing Botfly

If you’re planning to travel to places where botfly infestations are common, it’s important to understand how they spread and what an infestation looks like. These areas include Central America, South America, and Africa. It’s recommended to take precautions such as wearing protective clothing, using insect repellant, and sleeping under mosquito nets. This will help you avoid contact with creatures that carry botfly larvae.

You can also learn more about botfly infestations and general health advice for travelers from the website of the Centers for Disease Control and Prevention (CDC).