Vet on Call: These flies will eat your animals alive

This would sound strange and scary. Do you know that there are flies that can feed on you and your animals as you go about your business?

The flies cause an ailment known as myiasis, which is one of the neglected diseases in the world resulting in people having little knowledge of its presence.

My search on myiasis in Kenya only returned one short case report of the disease in a free ranging wild eland, published by scientists at the Kenya Wildlife Service in 2013. The authors concluded their report showed myiasis exists in Kenya.

The disease is a parasitic infestation of livestock or human beings by fly larvae (maggots) that grow inside the host while feeding on its tissue.

Two weeks ago, I visited three sub-counties of Kitui County and the presence of myiasis in dogs and goat kids was surprisingly high. The disease is locally called “mienya”. Almost every dog I encountered had the ugly skin condition.

A few adult goats also showed infection but the kids were more affected. I was told by a number of dog owners that the disease has been common and more severe during this rainy season. In some cases, some children had also been affected but not as severely as the dogs and goat kids.

I am a regular visitor of Kitui having discovered my missing rib in that region many years ago. I have, however, not seen myiasis affecting domestic animals so widely and severely.

Many of the villagers knew about the disease and its cause but they did not know how to prevent and control it. One person who declined to be identified or photographed swore he gave his dogs Panadol and they always recovered but the puppies died.

Well, this gentleman may be very happy with his “treatment” but the truth is that the infecting agents just ate enough from the dog and then dropped to the ground to complete their life cycle. The dog healed the wounds on its own.

The only thing Panadol could do is reduce itching, swelling and pain but is not known to have any effect on the invading worms.

FLIES THAT HAVE FLESH-EATING LARVAE

Once back in Nairobi, I reported my observation to the national Director of Veterinary Services (DVS) and his chief officer in-charge of disease control. They later informed me they were following up with the County Director of Veterinary Services in Kitui.

I explained to residents with affected animals the cause and management of myiasis. Two people had reported to their local veterinary service provider and their dogs and goats had been injected with the correct medicine.

However, they were still not taking preventive measures and it would only be a matter of time before the animals were infested again.

Myiasis occurs when flies that have flesh eating larvae lay their eggs on the intact skin of animals or humans, on wounds or on wet sweaty skin in case of animals with long hair or unkempt hair in humans.

Such flies are known as myiasis-causing flies. They are from different families but all belong to one group called dipterans.

These are flies with a single pair of wings. There are three types of myiasis. First is the obligate myiasis. The larvae in this case have to develop in a live animal then drop to the ground to form the pupa and mature into the adult fly.

Once the fly lays the eggs on the intact skin or on wounds, they hatch into the larvae which burrow into the skin. The skin reacts to the foreign body and its secretions and forms a nodule that may be reddened, itchy and swollen.

Flies that may cause the disease include the sheep, cow and human botflies. The worms usually seen in the nose and brain of sheep are larvae of the sheep botfly. Others are the Old and New World Screworms.

The second type of myiasis is termed as facultative. In this case, the fly larvae may grow on existing wounds, foul discharge or rotting plant matter.

The flies do not purposely search for live animals with wounds to lay their eggs but they are attracted by blood or foul smell.

The larvae develop in the decomposing animal tissue and fall to the ground to pupate and mature into the adult fly once the larval stage is fully developed. Flies in this group include the green and blue bottle flies.

HIGH LEVEL OF HYGIENE

Finally, there is the accidental myiasis. The larvae of flies in this group do not require a live host to develop and mature.

The flies encounter wounds by chance in the course of their feeding and they lay eggs on them. These larvae do not burrow into live tissue but feed on decomposing tissue.

The most commonly encountered flies in this group are the common house fly and the latrine flies.

Myiasis, therefore, is the presence of worms that are fly larvae, in the body of a living animal or human. The worms are called maggots.

Affected site is disgusting to the eye and very uncomfortable to the victim. The secretions and proteins of the larvae cause itching, reddening, swelling and pain; accompanied by death of tissues at the affected site.

The infected areas may also ulcerate and get bacterial infection. Infected animals lose weight, become sickly and fail to thrive.

Some may die due to spread of toxins and bacteria from the sites of infestation to the rest of the body thereby causing blood poisoning. This is medically called septicaemia.

The best way of dealing with myiasis is to prevent flies from accessing the animals or humans. High levels of hygiene should be practised by keeping the skin clean and the hair dry. In animals with long hair, the coat should be kept short and straightened.

The animals’ sleeping areas should be dry of water and urine to prevent development of skin wounds that attract flies.

Both dogs and livestock should be washed at least once per week with insecticides that have residual protection.

Pyrethroids such as cypermethrin are recommended because they kill flies, mites and ticks in addition to their residual activity.

Myiasis in animals is effectively treated with ivermectin injections which are legally only administered by licensed veterinary doctors or veterinary paraprofessionals.