Glossina, Chrysops and Tabanus

At a glance

Shape

Tsetse: brown fly whose wings fold flat over the back like closed scissors, with a forward-pointing proboscis; tabanids: stout flies with large, often coloured eyes

Family

Glossinidae (tsetse); Tabanidae (Chrysops, Tabanus)

Type

Blood-feeding dipteran insects (biological and mechanical vectors)

Size

Tsetse about 1 cm; horse flies up to a few centimetres

Morphology

• Tsetse flies have a rigid piercing proboscis and a hatchet-shaped cell in the wing.
• Both male and female tsetse flies take blood.
• Tabanid females have cutting mouthparts that tear the skin and cause a painful bite.

Transmission

• Tsetse: the fly ingests trypanosomes from an infected person or animal; after about three weeks it injects infective forms in its saliva.
• Chrysops: day-biting females ingest Loa loa microfilariae and later deposit infective larvae on the skin.
• Tabanids and deer flies can also carry some pathogens mechanically on their mouthparts, for example in tularaemia.

Reservoir: Humans (T. b. gambiense; Loa loa); Wild and domestic animals, especially cattle and antelopes (T. b. rhodesiense)

Vector: Glossina is the only vector of human African trypanosomiasis; Chrysops silacea and C. dimidiata carry Loa loa in the rain forests of West and Central Africa.

Isolation precautions

What the care team adds to standard precautions.

• Standard

Life cycle

1. The tsetse female does not lay eggs: she nourishes one larva at a time inside her uterus.
2. She deposits a fully grown larva on shaded soil, which burrows in and pupates within hours.
3. The adult emerges weeks later; a female produces only a few offspring in her life, so populations grow slowly.
4. In the tsetse, trypanosomes multiply in the midgut, then move to the salivary glands to become infective.
5. Tabanids lay egg masses on plants over water or mud; larvae grow in wet soil and pupate there.
6. In Chrysops, Loa loa microfilariae become L3 larvae in the thoracic muscles and migrate to the proboscis.

Virulence factors

• Tsetse bites can leave a trypanosomal chancre at the bite site, especially with T. b. rhodesiense.
• Day-biting habits overlap with farming, fishing and forest work.
• Slow tsetse reproduction makes traps and insecticide-treated targets effective for control.
• Painful tabanid bites interrupt feeding, so the fly moves between hosts and can carry blood mechanically.

Diseases it causes

• Human African trypanosomiasis (sleeping sickness), carried by tsetse flies Human African trypanosomiasis (sleeping sickness) →
• Loiasis (African eye worm), carried by Chrysops deer flies
• Tularaemia, which can follow deer fly bites Tularaemia →

Clinical picture

• Painful tsetse or horse fly bite; a chancre may form at the bite site within days.
• Sleeping sickness: fever and lymph nodes first, then confusion and disturbed sleep.
• Loiasis: transient Calabar swellings and a worm crossing under the conjunctiva.

Diagnosis

• Entomology: identifying tsetse by the wing fold and wing cell pattern; tabanids by eyes and wings.
• Patient with sleeping sickness: trypanosomes in chancre fluid, blood, lymph node aspirate or cerebrospinal fluid.
• Loiasis: microfilariae in blood drawn around midday, or the adult worm seen in the eye.

Treatment

Does not apply to the insect. Sleeping sickness is treated with antitrypanosomal drugs chosen by subspecies and stage (pentamidine, fexinidazole, nifurtimox-eflornithine, suramin, melarsoprol); loiasis with antifilarial drugs, with caution in heavy infections.

Drug class only; doses and regimens are set by the clinician from the current guideline.

In Pharmacology:

• Pentamidine
• Diethylcarbamazine
• Albendazole

Prevention

• Tsetse traps and insecticide-treated targets or cloth screens; they work because tsetse breed slowly.
• Neutral-coloured clothing, as tsetse flies are drawn to dark blue and black.
• Long clothes during the day in forest and river areas.
• Active screening and treatment of people in endemic areas to remove the human reservoir.

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Connections

← Back to the group: Arthropod vectors

Educational content on microorganisms; not a treatment guide and no substitute for a health professional's advice. No doses are given.

Sources: Trypanosomiasis, human African (sleeping sickness) (WHO, 2025); CDC - DPDx - Trypanosomiasis, African (CDC, 2024); CDC - DPDx - Loiasis (CDC, 2024); About Tularemia | Tularemia | CDC (CDC, 2024).

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Representative model, for educational purposes only.