Dictionary of Tropical Medicine


An almost invariably fatal viral infection of the CNS in mammals. Caused by a rhabdovirus and mostly transmitted by bite. While there is no effective treatment for the infection, it can be prevented by the use of a human diploid vaccine if given before the onset of symptoms.

Radical surgery

An operation to remove a cancer, plus adjacent tissue and lymph nodes.


A cancer that responds to radiotherapy.


A treatment which uses atomic particles and high energy rays to destroy cancerous cells.

Random sampling

The sampling process whereby each unit in the population has an equal chance of being selected.


A rate is the frequency with which a health event occurs in a defined population. The components of the rate are the numbers of deaths or cases (the numerator), the population at risk (denominator), and the specified time in which the events occurred. All rates are ratios, calculated by dividing the numerator by the denominator.

Reaginic antibody

As used by immunologists, this term refers to IgE antibodies. As used by microbiologists, it refers to antibodies produced in syphilis probably in response to the tissue damage caused by Treponema pallidum. Production of these antibodies in patients with syphilis has been utilised in the development of the non-treponemal serological tests for syphilis such as the VDRL Test, the RPR Test and the now superceded Wasserman Complement Fixation Test. These tests are useful in that they are only positive in active syphilis but they have many biological false positive reactions, including pregnancy.


Reactivation of infection; in malaria, renewed manifestation of infection due to survival of RBC forms.

Red back spider

Spider found mostly in Australia and is similar to the Black Widow of America and the Button spider of South Africa. Belongs to the species Latrodectus hasseltii.

Red tide

The appearance of a reddish-brown scum on the surface of the sea caused by dinoflagelates at certain times of the year when heat and other climatic conditions allow for vast expansion in their numbers. Unlike the dinoflagellates that cause PSP, they seems to cause no medical problem apart from irritation of the eyes (conjunctivitis), foul-tasting sea water, and leaving a rotting, unpleasant smell when they dry out on the beach.

Reduviid bugs

Blood sucking hemipterans found in Latin America and which serve as vectors for Trypanosoma cruzi, the cause of Chagas Disease. These insects are also known as cone nose bugs, assassin bugs or triatomids. They belong to the family Reduviidae and the genera Rhodnius and Triatoma, Panstrongylus amongst others.

Reef spawn

Colloquial term for red tide. Contrary to the popular belief this has nothing to do with the spawning of the reef seen at set times of the year.


Resistant to ordinary treatment or infection.


Recurrence of malarial parasitaemia with fresh infection of RBC's by merozoites derived from hypnozoites in the liver. The reappearance of a disease after a period when the symptoms lessened or ceased. A renewed manifestation of clinical symptoms and/or parasitaemia associated with malaria infection, separated from the previous manifestation by an interval greater than the one reflecting the normal periodicity of paroxysms.


The period when the symptoms or signs of a disease have ceased.

Renal failure (acute)

Inefficient functioning of the kidney, leading to death unless acute medical attention is available. Envenomation (especially snake bite) is a common cause, as well as a range of medical conditions, including infection..

Representative Sample

A sample that gives an indication of the composition of the whole population.


The surgical removal of tissue.

Reservoir host

An animal species which carries a pathogen without detriment to itself and serves as a source of infection. Host which acts as a reservoir of the infection in nature.

Reservoir of infectious agent

Any human beings, animals, arthropods, plants, soil, or inanimate matter in which an infectious agent normally lives and multiplies and on which it depends primarily for survival, reproducing itself in such manner that it can be transmitted to a susceptible host.


An inherited ability of a pathogen or vector to survive treatment with a chemical designed to kill it. The ability of a parasite to live in the presence of a drug, that would normally kill members of the same species.

Resistance (Host)

The sum total of body mechanisms which interpose barriers to the progress of invasion or multiplication of infectious agents, or to damage by their toxic products.1. Immunity - That resistance usually associated with possession of antibodies having a specific action on the microorganism concerned with a particular infectious disease or on its toxin. Passive immunity is attained either naturally, by maternal transfer, or artificially, by inoculation of specific protective antibodies (convalescent or immune serum or immune serum (gamma) globulin (human) and is of brief duration (days to months). Active immunity lasting months to years is attained either naturally, by infection, with or without clinical manifestations, or artificially, by inoculation of fractions or products of the infectious agent or of the agent itself, in killed, modified or variant form.2. Inherent resistance - An ability to resist disease independently of antibodies or of specifically developed tissue response; it commonly rests in anatomic or physiologic characteristics of the host; it may be genetic or acquired, permanent or temporary.

Respiratory arrest

Cessation of breathing, often caused by envenomation (or poisoning).

Resting habits

The habits determining the places and times of day or night that mosquitoes rest.


A muscular structure of three parts proximal bulb, narrow isthmus and distal body or corpus as in free-living rhabditoids, parasitic oxyuroids, and free-living and non-infective stages of Strongyloides spp.


A member in the Order of jellyfish having 8 modified mouth arms armed with nematocysts, rather than the usual tentacles. Each mouth arm has numerous small mouth openings rather than the usual single manubrium.

Rhopalium (pl. rhopalia)

The specialised structures present in the sensory niches between the four pedalia of cubozoan (box) jellyfish. It houses the ocellus (eye) and statocyst (balance organ). Rhopalia are also present, although less obvious, in scyphozoan jellyfish.


Microbial agent(s) appearing like small bacteria and multiplying by simple fission, but only within a living host cell.


See tinea.


The probability of harmful consequences arising from a hazard.

Risk Factor

An aspect of personal behavious or lifestyle, an environmental exposure, or an inborn or inherited characteristic that is associated with an increased risk of a person developing a disease.


Ribonucleic acid. A type of nucleic acid that carries the message coded in DNA (the genes) to the manufacturing system of the cell.

Romanas Sign

Oedema of the eyelid in early Chagas Disease (South American trypanosomiasis) due to the infected faeces of the vector assassin (triatomid) bug causing swelling of the mucosa of the eye.

Ross River Fever

See Epidemic Polyarthritis, Ross River Virus.

Ross River virus

A mosquito-borne arbovirus causing epidemic polyarthritis in Australia and certain islands of the Western Pacific to which it has spread.


The protuberant anterior part of the scolex of certain tapeworms. May be unarmed or armed with rows of hooklets.