Dictionary of Tropical Medicine

T-cell

A specialised white cell (lymphocyte) responsible for cell-mediated immunity. See also T-lymphocyte.

T-helper cells

A type of lymphocyte which assists the B-Lymphocytes in producing antibodies.

T-lymphocytes (or T-cells)

White blood cells that have matured in the thymus gland. There are at least two kinds of T-lymphocytes - helpers and suppressors. In AIDS, the number of helper cells is decreased.

T-suppressor cells

A type of T-lymphocyte that stops antibody production when the invading antigen has been inactivated.

Trichostrongylus

A genus of animal parasitic intestinal nematodes. Can infect humans. The egg, passed in the faeces, is similar to, and is often confused with, hookworm.

Tachycardia

Excessively above normal rate of heat beat.

Tachypnoea

Excessively above normal and rapid breathing rate.

Tampan

A soft tick (Argassid). The genus Ornithodoros are vectors of endemic relapsing fever due to Borrelia recurrentis (= B. duttoni).

Tamponade

An increase of fluid around the heart.

Taxonomic study

Identification of species and their genetic relationship to one another.

Taxonomy

Systematic binomial classification of all living things.e.g. KingdomPhylumClass Order FamilyGenus Species

Tefanoquine

A primaquine analogue discovered by the US Army with activity against liver parasites of malaria and able to suppress blood parasites and kill gametocytes. See also Etaquine.

Telamon

A cuticular thickening of the ventral wall of the spicular pouch in nematodes. Both gubernaculum and telamon are for guiding the spicules out of the body. Shape and size and number of the spicules, gubernaculum and telamon are also used for identification of the nematodes.

Tenesmus

Painful but ineffectual attempts at defaecation.

Tentacle

Long, usually-thick, hair-like structures that contain the nematocysts needed for the capture of food. They may also be used to deliver such food to the mouth of the jellyfish. They may contract up to a tenth of their extended state.

Teratoma

A neoplasm possibly starting in the foetus and having different types of tissues; e.g., ovarian teratoma often have teeth, adenoma, and connective tissue proliferation.

Tetanus/Tetany

Violent spasms, muscle contraction ("lock-jaw") caused by a spore-forming, Gram positive bacillus penetrating the body though a puncture wound, and usually leading to death. The organism occurs in water and may occur after envenomation (eg in stingray spine puncture wounds), as well as the more commonly-known soil contamination (eg in war wounds). It may be prevented by vaccination with tetanus toxoid.

Tetrodotoxin

The toxin responsible for envenomation in blue-ringed octopus and Japanese Fugu (tetrodotoxic) poisoning from puffer fish ingestion.

Therapeutic

Refers to a treatment for the cure or control of a disease.

Tick bite fever

Tick-borne spotted fever.

Tick typhus

Tick-borne spotted fever.

Tinea

Also called ringworm. Refers to a variety of superficial fungal infections of the skin on different areas of the body caused by dermatphyte fungi belonging to the genera Epidemophytum, Microsporosum, and Trichophytum..

Tissue

A collection of cells similar in structure or function.

Tourniquet

A very tight ligature applied over the proximal portion of an extremity (limb) to occlude the artery to prevent blood reaching the distal part of the limb. Useful for severe, uncontrolled arterial bleeding, but dangerous when used for envenomation.

Tourniquet test

A positive tourniquet test with scattered fine petechiae is one of the earliest clinical signs in dengue haemorrhagic fever.

Toxicity

The ability to cause ill effects. Poisoning.

Toxin

Any poisonous substance of microbic, vegetable or animal origin. A substance that is harmful to the tissues.

Toxoplasmosis

A zoonotic disease caused by the apicomplexan protozoan Toxoplasma gondii. The definitive hosts of this parasite species are felids (cats).

Trachoma

An eye infection causing a purulent conjunctivitis and which can lead to blindness unless treated. Caused by Chlamydia trachomatis serotypes A, B and C.

Transmission

Any mechanism by which a susceptible human host is exposed to an infectious or parasitic agent. These mechanism are:-1. Direct transmission: Direct and essentially immediate transfer of infectious agents (other than from an arthropod in which the organism has undergone essential multiplication or development) to a receptive portal of entry by which infection of humans may take place. This may be by touching, as in kissing, sexual intercourse or biting (direct contact); or by the direct projection of droplet spray onto the conjunctivae, or onto the mucous membranes of the nose or mouth during sneezing, coughing, spitting or talking (usually not possible over a distance greater than 3 ft) (droplet spread); or, as in the systemic mycoses, by direct exposure of susceptible tissue to soil, compost or decaying vegetable matter that contains the agent and where it normally leads a saprophytic existence. 2. Indirect transmission: (a)Vehicle-borne - Contaminated materials or inanimate objects such as toys, handkerchiefs, soiled clothes, bedding (fomites), surgical instruments or dressing (indirect contact); water, food, milk, biological products including serum and plasma, or any substance serving as an intermediate means by which an infectious agent is transported and introduced into a susceptible host through a suitable portal of entry. The agent may or may not have multiplied or developed in or on the vehicle before being introduced into man. (b) Vector-borne (i) Mechanical:- Includes simple mechanical carriage by a crawling or flying insect through soiling of its feet or proboscis, or by passage of organisms through its gastrointestinal tract. This does not require multiplication or development of the organism. (ii) Biological:- Propagation (multiplication), cyclic development, or a combination of them (cyclo-propagation) is required before the arthropod can transmit the infective form of the agent to man. An incubation period (extrinsic) is required following infection before the arthropod becomes infective. Transmission may be by saliva during biting, or by regurgitation or deposition on the skin of agents capable of penetrating subsequently through the bite wound or through an area of trauma following scratching or biting. This is transmitted by an infected invertebrate host and must be differentiated for epidemiological purposes from simple mechanical carriage by a vector in the role of a vehicle. An arthropod in either role is termed a vector. (c) Air-borne: The dissemination of microbial aerosols with carriage to suitable portal of entry, usually the respiratory tract. Microbial aerosols are suspensions in air of particles consisting partially or wholly of microorganisms. Particles in the 1 to 5 micron range are quite easily drawn into the lungs and retained there. They may remain suspended in the air for long periods of time, some retaining and others losing infectivity of virulence. Not considering as airborne are droplets and other large particles, which promptly settle out; the following are airborne, their mode of transmission indirect: (i) Droplet nuclei: Usually the small residues which result from evaporation of droplets emitted by an infected host. Droplet nuclei also may be created purposely by a variety of atomising devices, or accidentally, in microbiology laboratories or in abattoirs, rendering plants, autopsy rooms, etc. They usually remain suspended in the air for long periods of time. (ii) Dust: The small particles of widely varying size which may arise from contaminated floors, clothes, beddings, other articles; or from soil (usually fungus spores separated from dry soil by wind or mechanical stirring).Note: Air conditioning and similar air circulating systems may play a significant role in air-borne transmission (e.g. Legionnaires disease).

Transport host

An animal merely acting as a transporter for a parasite, c.f. Paratemic host.

Trap nets

Nets used to sample the living mosquito population. By permitting access to a bait but restricting movement away from it, trap nets tend to concentrate female mosquitoes near the bait.

Trauma

An injury to the body from a mechanical force.

Travel medicine

That aspect of public health which seeks to prevent illnesses and injuries occurring to travellers, especially those going abroad, and manages problems arising in travellers coming back or from abroad. It is also concerned about the impact of tourism on health and the provision of health and safety services for tourists.

Travellers Diarrhoea

Diarrhoea frequently recorded from travellers, especially those visiting tropical or developing regions of the world. Probably the commonest travel-related infection. Although it can be caused by a range of viral, bacterial, protozoan and even on occasions, fungal and helminthic agents, in excess of 80-90% of cases are due to enterotoxigenic Escherichia coli (ETEC) or less commonly enteroadherent Esch. coli (E.Ad.EC).

Trophozoites

The motile, feeding stage of protozoan parasites.

Tropical eosinophilia

A syndrome found in certain tropical areas in which patients present with hypereosinophilia, pulmonary infiltration, cough, chest pain and asthma-like attacks. Associated with infection by the filarial nematodes Wuchereria bancrofti and Brugia malayi. These infections are usually amicrofilaraemic, , especially in expatriates, i.e. no microfilariae can be detected in peripheral blood.

Tropical Medicine

In simple terms, tropical medicine is the medicine practised in the tropics. It arose as a discipline in the 19th century when physicians responsible for the health of colonists and soldiers from the dominant, European countries were faced with diseases not encountered in temperate climates. With extensive worldwide travel possible today, tropical diseases are now being widely seen in returning travellers and expatriates.

Tropical sprue

A chronic malabsorptive, diarrhoeal, steatorrhoeic condition of unknown aetiology but often associated with secondary bacterial involvement.

Tropical ulcer

A cutaneous ulcer seen particularly in malnourished individuals. The cause of these ulcers is often ascribed to a synergistic infection by the spirochaete Treponema vincentii and the anaerobic Gram negative rod, Fusobacterium nucleatum.

Tropism

An affinity for a particular organ or body system (e.g. neurotropic).

Trypanosomiasis

A disease caused by parasites of the genus Trypanosoma and including sleeping sickness in Africa and Chagas disease in Central and South America.

Tsetse

A biting fly found in Africa, genus Glossina, which may transmit sleeping sickness.

Tularaemia

A zoonotic infection of rabbits and other small mammals, caused by the Gram negative rod, Francisella tularensis.

Tumour

A mass or swelling. The lump can be a neoplasm (benign or malignant) or a tumour can be a mass due to an infection or inflammation.

Typhoid (Enteric) fever.

A septicaemic infection of humans caused by Salmonella typhi. A similar but generally milder enteric fever, paratyphoid, is caused by Salmonella paratyphi A,B,C.

Typhus

A louse-borne febrile illness of humans caused by Rickettsia prowazekii, A similar but milder zoonotic illness is murine typhus, caused by R. typhi harboured by rodents and transmitted by the tropical rat flea, Xenopsylla. The so-called tick typhus group of diseases are better called spotted fevers.