Since mid-2019, the people of Murang'a County in Kenya have experienced what they call "a mysterious worm infection" which causes their skin to itch and then swell, resulting in oozing boil-like wounds. This infection, known as myiasis, is an infestation of organs and tissue caused by larvae of dipterans (flies) - in Africa the disease is commonly caused by the Cordylobia anthropophaga (tumbu fly) and the Dermatobia hominis (bot fly) in Latin America.
The infection is commonly reported in domestic and wild animals - and occasionally in humans.
Myiasis infestation happens worldwide. Its prevalence is mainly influenced by latitude, season and life cycle of the myiasis flies. Infection rates are higher in the tropics and sub-tropics.
In Kenya, myiasis is known to be endemic in south eastern counties like Kitui.
The most common in people is cutenous mysiasis. This occurs when the larvae penetrate the skin and develop in the tissues. It mainly presents in two forms: wound myiasis and furuncular (follicular) mysiasis. The rare forms include nasopharyngeal (which affects the nose, sinuses and pharynx); phthalmomyiasis (which affects the orbits and orbital tissues of the eyes); intestinal urogenital; involves the alimentary tract and urinary tract respectively. The rarest is haematophagous myiasis which causes funicular lesions on infants' faces, especially rural areas.
Myiasis is a neglected tropical disease. It can cause severe clinical outbreaks in humans and animals, with potential economic losses in the livestock industry. But the good news is that it is preventable.
Myiasis in Kenya
The current outbreak reported from mid-2019 Murangá is only the most recent. Outbreaks have previously been reported in humans, their livestock, and even wild animals in Kenya. Human cases ranged from minor to life threatening conditions.
Cases of acute furuncular myiasis were reported in children and domestic animals between mid to end of 2018 in Kitui county - a known tumbu fly endemic zone. The locals knew the cause of the disease and its symptoms, but didn't know how to prevent or treat it. The infected animals became sickly, lost weight and failed to thrive. Others died from blood poisoning due to spread of toxins and bacteria from infestation sites to the rest of the body. Similarly, in 2014, three women who had travelled to Kitui were treated for furunculosis at a Nairobi hospital.
Between May and December 2012 cases of traumatic wound myiasis were reported in free-ranging elands in Kigio wild-life conservancy in Nakuru county. The infected animals lost their balance, hearing and sight, resulting in emaciation and the animals becoming easy prey to predators.
What causes it?
Furuncular myiasis caused by C. anthropophaga, is the most common type in Kenya and Africa. People are likely exposed when they spread their clothes outside to dry. The flies lay their eggs on these clothes and the hatched larvae can survive on the clothes for up to 15 days. Once the clothes are worn, the body heat activates the larvae which penetrate the skin with their sharp mandibles.
But in the case of Dermatobia hominis, a common cause of mysiasis in south and central America and Trinidad, the infection occurs when mosquitoes or ticks that act as a means of transport for myiasis flies eggs, bite. As the mosquito takes its blood meal, the body heat induces the eggs to hatch into larvae which painlessly enters the hosts through the bite wound.
Since myiasis is caused by flies. It's important to prevent them from coming into contact with people. This can be done by using window screens, sleeping on raised beds and under mosquito nets at night. Insect repellents, using insecticides and wearing protective clothing can also help.
Hang clothes to dry in the sun as this helps to remove any residual eggs. Avoid spreading clothes on the ground.
Hot iron clothes. The heat destroys both the eggs and larvae.
Tumbu fly are attracted to urine so wash, dry in the sun and hot iron urine wetted children's bedding.
Shave hair or keep the scalp clean and dry. The scalp especially when hair is unkempt is usually most infested.
Dry and clean floors. Damp and wet floors predispose occupants to infestation.
Improve general hygiene and sanitation. For example remove rubbish from living areas.
Cover wounds with new dressing daily to prevent flies from reaching the skin.
What can government do
Short term solutions:
Health education in endemic areas on how to identify and prevent the infestation and where to seek for medical help in cases of infection.
Distribute nets and window screens in endemic areas especially when infestations are likely to spike during the wet and rainy seasons.
Long term solutions:
Employ extension agricultural officers who can assist in surveillance and control of myiasis in livestock.
Employ wildlife officers for surveillance and control of myiasis in wildlife.
Improve the socio-economic standards of the citizens so that they might build better houses. Infestations are known to rise in mud houses.