Dictionary of Tropical Medicine

Pacific man-o'war

The colloquial term for the multi-tentacled hydrozoan colony Physalia physalis, recently described on the eastern coast of Australia.


A widespread epidemic which may affect large areas of the world.


Benign epithelial neoplasm in which neoplastic cells cover finger-like processes of dermis. Also any benign epithelial neoplasm growing outward from an epithelial surface.

Paralytic shellfish poisoning

Poisoning by saxitoxin, a toxin present in some shellfish, usually in tropical or sub-tropical seas. Symptoms of respiratory arrest, or brain involvement occur in some 8% of cases, resulting in death. Saxitoxin is related to tetrodotoxin.


Parasites circulating in the blood stream.


A plant or animal which lives upon or within or upon another living organism at whose expense it obtains some advantage without compensation. By convention, human parasitology covers the study of the protozoa, helminths and arthropods infecting humans.

Parasite density

The number of malaria parasites in a specified volume of blood.


A type of association where one organism depends for metabolism on the other.

Paratenic host

An intermediate host which becomes infected by consuming another intermediate host and in which the parasite does not develop any further than in the first intermediate host. Also called a transport host.


Administration, other than orally, of a substance e.g. intramuscular or intravenous.


Tingling and burning in the skin frequently described as "pins and needles". It is caused by irritation of cutaneous nerves by a variety of causes including trauma and envenomation.

Parous rate

The proportion of female mosquitoes that have laid eggs at least once. Use for age-grading a mosquito population.


Cyclic manifestation of acute illness in malaria, characterised by a rise in temperature with accompanying symptoms, usually caused by invasion of the blood by a brood of parasites released from RBC's.


An organism or substance which caused diseases.


Ability to cause disease.


A doctor that specialises in the interpretation of changes in tissues.


The study of how disease changes the anatomy (histopathology-and histology) of tissues.

Peak biting time

The period during which the biting cycle of a given mosquito species when the largest number of females take blood meals.

Pedalium (pl. pedalia)

The four flattened "corners" of cubozoan (box) jellyfish from which arise the tentacles - unlike other jellyfish where the tentacles arise from many, or any, areas of the bell.


A parasitic infestation of the head, the hairy parts of the body and the clothing by adult lice, larvae and nits (eggs), which often results in severe itching and excoriation of the scalp and body. Secondary infection can occur. Infesting agents include Pediculus capitis, the head louse, P. humanus, the body louse, and Pthirus pubis, the crab louse, which usually infest the pubic region, but may also infest the hair of the face, axillae and the body surfaces.


The open sea (ocean) habitat of some animals.


A syndrome resulting from niacin deficiency, associated with photosensitive dermatitis, mucous membrane inflammation, diarrhoea and psychiatric disturbances.


Recurrence at regular intervals of symptoms in malaria, characterised clinically by paroxysms and resulting from the invasion of the blood by new generations of parasites. Periodicity may be quotidian, tertian, quartan or double quartan according to the intervals between paroxysms.


Recurrence at regular intervals of symptoms in malaria, characterised clinically by paroxysms and resulting from the invasion of the blood by new generations of parasites. Periodicity may be quotidian, tertian, quartan or double quartan according to the intervals between paroxysms. Periodicity also used to refer to the cyclic appearance in the blood of microfilariae of Wuchereria bancrofti (nocturnal) and Loa loa (diurnal).

Persistent Chronic Diarrhoea

Diarrhoea that begins acutely but lasts more than 21 days. The usual enteropathogens are Shigella spp., Salmonella spp., Campylobacter jejuni, Yersinia enterocolitica, Capillaria philippinensis, Cryptosporidium. Giardia can also be a cause.

Person/vector contact

The number of times a person is bitten by a vector mosquito, normally expressed as the number of bites per person per night.


Pin point haemorrhages.

Peyers patches

Group of lymphoid tissue in the small intestine, especially involved in typhoid infections.


A group of biting flies commonly called sandflies including the genus Phlebotomus, sometimes vectors of leishmaniasis.


The taxonomic group below a Kingdom, and above a Class. See Taxonomy.


A nonvenereal tropical treponemal disease similar to yaws and caused by Treponema pertenue.


Apicomplexan protozoa of the genus Babesia. Transmitted by Ixodid ticks and cause diseases such as red water fever in cattle and biliary fever in dogs. Rare human infections are recorded, especially in the splenectomised.


An inert substance with no actual effect, but administration of which may produce a beneficial effect to help a patient (eg pain relief).


Any self-replicating genetic component of a cell, e.g. bacteria, which is outside the chromosomes.


The platypus, Ornithorhynchus anatinus is found in fresh water streams along the eastern seaboard of Australia from Cooktown, in northern Queensland, to Tasmania. It is an unusual looking, furry mammal with a bill like a duck, webbed feet with claws (used for digging burrows), and a paddle-like tail for swimming. The male has spurs on its hind legs connected to venom glands. Venom injection causes excruciating, long-lasting pain needing hospital admission and treatment. Although never fatal in humans, death has occurred in hunting dogs.


The third stage larva of pseudophyllidean tapeworms, which has a solid body.


A toxin which introduced to the body via the gastrointestinal tract or the respiratory tract.


Inflammation in several joints. Common features of a number of arboviral infections (e.g. Ross River virus and Barmah Forrest virus infections).


Wide varieties of form of a species.


The immature life-cycle form of a jellyfish (or other cnidarian) which is attached to a substrate. Tumour projecting from mucosal surface.

Portuguese mano'-war

The colloquial term used for the multi-tentacled hydrozoan colony of Physalia physalis common in the north Atlantic Ocean.

Potentially Pathogenic Environmental Mycobacteria (PPEM)

The atypical mycobacteria. The commonest PPEM to cause human disease is the Mycobacterium avium-intracellulare complex. PPEM differ from M. tuberculosis in their source (environmental or zoonotic), rate of growth, temperature of growth and ability to produce pigment on culture. Mostly infect immunologically compromised humans and the disease caused by some species may be clinically indistinguishable from true human tuberculosis.


(see Purified protein derivative)


A broad spectrum anthelmintic very effective against many human trematodiases (including all forms of schistosomiasis) and some cestode infections (e.g. hymenolepiasis; cysticercosis).

Predictive Value Negative

The probability that a person with a negative test is free of the disease and is not a false negative.

Predictive Value Positive

The probability that a person with a reactive test has the disease and is not a false reaction.

Preferred breeding sites

Sites suitable for egg-laying and satisfactory for all aquatic stages of development.

Prepatent Period

Time of infection (bite) to the first finding of the organism (eg, malaria parasite) in the bloodstream, i.e. from the time of infection to time when first diagnostic stages can be detected.


The number of cases of a disease or other condition existing for a given area or at a given time, for a given population. Prevalence includes both new (incidence) and existing instances of a disease.

Prevalence rate

quotient using as the numerator, the number of persons sick or portraying a certain condition, in a stated population, at a particular time, regardless of when that illness or condition began, and as the denominator, the number of persons in the population in which they occurred.


Used for radical cure of malaria and to prevent relapse. It is used to kill the liver stages of the malarial parasite. It also has the potential to be used as a causal prophylactic drug. This 8-aminoquinoline must be used with care or not at all in people who are G6PD deficient.

Primary cancer

An original cancer still at the site at which it started to grow.


Formally known as the slow viruses. Prions are in reality transmissible abnormal proteins infecting the CNS. They cause such human diseases as Kuru, Creutzfeld-Jacob Disease (CJD), bovine spongiform encephalitis (mad cow disease) all of which are characterised by their extremely long incubation period.


The second stage larva of pseudophyllidean tapeworms which bears six hooks near the posterior end.

Prodromal period

Premonitory period; indicating the approach of a disease.


A premonitory symptom or precursor; a symptom indicating the onset of a disease.


Single segment of a tapeworm.


An estimate of the outcome of a disease. Poor prognosis indicates that outcome is liable to be fatal.


A biguanide antimalarial used alone or in combination for the prevention of malaria.

Proportional mortality rate (PMR)

A measure of the relative contribution to total mortality by a specific cause and these are expressed as number of deaths assigned to the state cause in a calendar year per 1000 total deaths in that year.


Molecular constituent of all cells comprising amino acid building blocks.


A gene in a cell that regulates cell growth and development in an orderly fashion. If a proto-oncogene mutates, it can give rise to cancer by causing growth without the normal controls. The proto-oncogene is then called an oncogene.


The scolex of a larval stage of the hydatid tapeworm. Morphologically it resembles the adult scolex.


The lowest division of the animal kingdom, including unicellular or acellular organisms with a eukaryotic structure.


The area of the body that is closest to the heart.




See paralytic shellfish poisoning.


Infestation with the crab (or pubic) louse, Pthirus pubis.

Pulmonary oedema

Fluid in the small air sacs of the lungs, from inefficient pumping by the heart or leakage of fluid from the blood vessels in the lungs (possibly from envenomation). As it prevents air exchange in the lungs it causes hypoxia and may lead to death.


The third stage in mosquito and other endopterygote insect development, emerging when the last larval instar shed its skin. Pupae swim but do not feed.

Purified Protein Derivative (PPD)

Reagent used by intradermal administration in the Mantoux (tuberculin) test for TB.P


A fever - a raised body temperature (above 37C in humans).


Fever causing