Dictionary of Tropical Medicine


Injection of a vaccine to prevent certain diseases. (Syn. immunisation).


A preparation of dead particulate or weakened bacteria or viruses prepared for injection into the body so that antibodies are formed to prevent disease (eg polio). Detoxified but genetically potent toxins (called toxoids) can also be used (e.g. tetanus and diphtheria)

Vas deferens

A canal connecting vas efferens to cirrus.

Vas efferens

A canal extending from a testis to the deferens.


Venereal Diseases Research Laboratory Test. One of the non-treponemal reaginic tests for syphilis.


An organism which carries or transmits a pathogen from a plant or animal to another plant or animal of the same species which is free of the disease. Anopheline mosquitoes are the vectors of human malaria.

Vector density

The number of a given vector species present. It may be expressed in relative terms (e.g., the biting density in relation to the human host) or in absolute numbers (e.g., the number present in a room, cattle-shed or artificial shelter).


A folded-in extension of the edge of the bell in the cubozoa which helps create a jet of water to propel the jellyfish forwards It may contract differentially to enable a change of direction.


A toxin which usually enters the body by injection through intact skin (e.g. a jellyfish sting or a snake bite by a venomous species).

Ventricular fibrillation

A very fast 'flickering' of the heart with no measurable circulation of blood by the heart. This usually occurs after a heart attack (or electrocution).


A fluid-containing blister on the skin, often quite itchy.


Acetic acid (4-6%) - this totally de-activates the nematocysts of all cubozoans (box-jellyfish) tested to date. Despite popular misconception it has no effect on the venom injected and does not help pain.


Presence of a virus in the blood.


Complete infective virus particle.


The relative infectiousness of a microorganism, or its ability to overcome the defences of the host.


An extremely small infective agent requiring living cells for replication. Are either RNA or DNA, never both.

Visceral larva migrans

The end results of heavy infection and migration of larva of Toxocara spp (especially T. canis - the dog Ascarid) in the viscera, producing a granulomatous reaction and pathology at the site.

Visceral leishmaniasis (Kala azar)

A protozoan disease caused by Leishmania donovani, found around parts of the Mediterranean basin, tropical Africa, South America, and central and eastern Asia. The disease is transmitted by female sandflies of the genus, Phlebotomus in the Old World and Lutzomyia in the New World. Full-blown disease is often fatal, if untreated. Growth nodules of the disease or leishmanioma form initially and, if spontaneous recovery does not occur, proliferating parasites burst out of the nodules, disseminating throughout the body.

Vitelline glands

The glands which provide substances for the development of the egg and the formation of the shell in trematodes and cestodes.


An opening of the female reproductive system, may be situated at the anterior, middle or posterior parts and on the ventral side of the body according to groups of nematodes.