Dictionary of Tropical Medicine

L1, L2, and L3

Immature developing (L1 and L2) and infective (L3) stages of nematode larvae, e.g. filariasis, hookworm etc.... In filariasis, after an infective blood meal, microfilariae exsheath, penetrate the stomach wall and pass into the haematocoele, from where they migrate to the thoracic muscles of the mosquito. In the thorax, the small larvae become more or less inactive, grow shorter but considerably fatter and develop, after 2 days, into "sausage-shaped" forms (L1). They undergo two (2) moults and the resultant third stage larvae (L3) become active. This is the infective stage and is formed some 10 days or more after the microfilariae have been ingested with a blood meal.

Lability

Chemical instability.

Larva currens

A rash rather like that of cutaneous larva migrans resulting from penetration of the filariform larva of Strongyloides stercoralis in the skin around the anus and buttocks, as part of autoinfection.

Larval habitat

The type of aquatic environment in which mosquito larvae are typically found.

Larval survey

The process of searching for mosquito larvae in a defined area. Larvae are collected and taken to the laboratory for identification and enumeration.

Larvivorous fish

Fish species which feed preferentially on mosquito larvae. They may contribute significantly to the reduction of vector densities.

Lassa Fever

A serious viral haemorrhagic fever of humans harboured by small rodents such as the multimammate mouse of West and Central Africa.

Latent period

The time between initiation of infection and the first shedding of the agent.

Latent stage

Resting or inactive stage found in some viral infections such as the herpes viruses.

Laticaudidae

Family name for sea snake kraits.

Leaf-crown

The cuticular extension to fine pointed processes in the nematodes which have no lip; extension from the rim of the mouth called "external leaf-crown", from the rim of the buccal capsule called "internal leaf-crown" as in Strongyloidea.

Leech

A blood-feeding annelid worm.

Legionnaires disease

Infection by the Gram negative rod, Legionella pneumophila and other species of the Genus. Often presents as an atypical pneumonia. Outbreaks have been reported from various countries.

Leishman-Donovan Bodies

(LD Bodies) Amastigote stages of protozoa of the genus Leishmania. These stages in a skin biopsy, bone marrow or spleen aspirate are diagnostic of Leishmaniasis.

Leptospirosis

A zoonosis. It is an acute, febrile, septicaemic disease caused by the Leptospira interrogans which has more than 200 serovars. The disease is characterised by a broad spectrum of clinical manifestations including fever, chills, headache, conjunctivitis and muscular pains. The disease may be subclinical in mild cases but jaundice and renal failure are observed in severe cases. Includes Weils Disease. Can result in an aseptic meningitis.

Leucocyte

A white blood cell.

Life cycle

The stages of development through which a plant or animal passes during its life. For mosquitoes these stages are: egg, larva, pupa, adult Normally, development of nematodes included four moults and five successive stages as follows: Egg, First-stage larva,(first moult),Second-stage larva, (second moult),Third-stage larva, (third moult), Fourth-stage larva, (fourth moult), adult. Generally, there are two types of life cycle for nematodes: direct and indirect types. 1. Direct Life Cycle: requires no intermediate host, after hatching from the eggs the larvae develop in the open from free-living to infective stages and gain access to the definitive host by mouth or penetration through skin. 2. Indirect Life Cycle: requires one or two intermediate hosts for development to infective stage.

Light traps

A mechanical trap which use a combination of light and/or carbon dioxide to attract and trap adult mosquitoes, e.g. Centres for Disease Control and Prevention (CDC) Light Trap.

Lion's mane

A colloquial term for Cyanea - used in many countries other than Australia.

Lionfish

See Scorpaenidae.

Lip

An extension of cuticle around the mouth of nematodes; there may be three, one dorsal and two subventral as in Ascaroidea or two as in Spiruroidea or absent as in Strongyloides and Filarioidea.

Little mauve stinger

Colloquial term for Pelagia noctiluca.

Louse

Insects belonging to the orders Anoplura (sucking lice) or Mallophaga (biting/feather lice). Human lice include the Head louse (Pediculus humanus capitis), the body louse (P.h.corporis) and the pubic louse (Pthirus pubis).

Lung flukes

Trematode worms infecting the lungs of humans and other crab-eating mammals. Belong to the genusParagonimus and are found in parts of Africa, Latin America, Asia and SE Asia.

Lyme Disease

A zoonotic disease caused by the spirochaete Borrelia burgdorferi and other species of the genus. Common in Europe and the USA and transmitted by Ixodid ticks.

Lymphadenopathy

Enlargement of the lymph nodes. Swelling of the body lymph glands which is sometimes painful, especially after envenomation. Lymph glands when swollen may be almost anywhere in the body, but are more easily felt in the neck, under the arms (axillae) and in the groins.

Lymphogranuloma venereum

(LGV) A tropical sexually transmitted disease caused by Chlamydia trachomatis serotypes L1, L2 and L3.

Lymphoma

A malignant neoplasm of lymphoid tissue.

Lyssa virus

A group of rhabdoviruses closely related to the rabies virus. The Australian Bat Lyssa virus is found in flying foxes (fruit bats) and can cause a rabies-like disease in humans. The disease should be handled as for rabies and can be prevented by using rabies vaccine.