Nematodes in the filariases in photos

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Wuchereria bancrofti and Brugia malayi

Distribution Wuchereria bancrofti

Distribution Wuchereria bancrofti is widely distributed throughout the tropics. Although normally nocturnal, a subperiodic diurnal form occurs in the Eastern Pacific. B. malayi has only been recognised in Asia. The periodic form occurs in India, SE Asia and Japan. The subperiodic form occurs only in Malaysia, Borneo and the Philippines.

Wuchereria bancrofti and Brugia malayi cycle

Wuchereria bancrofti and Brugia malayi cycle.

 Third-stage infective larvae (a) enter the mouthparts of the mosquito from which they penetrate the skin when the insect bites (b). They enter the lymphatics where the worms mature into thread­like adults (c) which can live for many years. Blockage of lymphatic vessels by the adult worms leads to elephantiasis (d) in some individuals. Larvae (e) are produced in the female worms and transform to microfilariae (f) which enter the peripheral circulation. From there they are picked up by mosquitoes with a blood meal (g). The microfilariae (h) penetrate the insect's gut wall to develop in the thoracic muscles (ij) in which they mature to the third stage larvae. {See also 214, 215, 225, 226, 234, 245.)

Larvae in mosquite thorax.

Photo 1. Larvae in mosquite thorax. Microfilariae in the peripheral circulation are ingested by mosquitoes when they suck blood. Microfilariae exsheath, migrate from the midgut, and penetrate the thoracic muscles where they mature to sausage-shaped first and second stage larvae, fx 100) Differential characters of some of the mosquito vectors, Mansonia, Culex and Aedes, are shown in 217-223 (see also 2-15; 768).

Infective larvae.

Photo 2. Infective larvae. After about two weeks they develop into third stage, filariform larvae which enter the proboscis. These infective larvae later penetrate the skin of a new host through the puncture wound made when the mosquito bites. (X20)

Female Aedes (Stegomyia) polynesiensis.

Photo 3. Female Aedes (Stegomyia) polynesiensis. Night biting Culex pipiens fatigans and various species of Ano­pheles are the main vectors of the nocturnal periodic form of VF. bancrofti. Day biting Aedes polynesiensis trans­mits the subperiodic form of W. bancrofti in various Pacific islands. Species of Mansonia are the main vectors of B. malayi. Compare the hump-backed stance with that of Ano­pheles. (x5)

Aquatic stages of Culex and Mansonia.

Photo 4. Aquatic stages of Culex and Mansonia. Unlike Anopheles mos­quitoes or those of Culex Mansonia larvae (5) and pupae (6) are attached by their breathing tubes (siphons) to underwater roots, stems and leaves of aquatic plants. Note the saw-edged tips of the siphons. Their ideal breeding habitats are open swamps with Pistia, water lilies and other aquatic plants. (X 60)

Aquatic stages of Culex and Mansonia (2).

Photo 5. Aquatic stages of Culex and Mansonia (2).

Aquatic stages of Culex and Mansonia (3).

Photo 6. Aquatic stages of Culex and Mansonia (3).

Tarsal claws of Aedes and Culex.

Photo 7. Tarsal claws of Aedes and Culex. The tarsal claws of Aedes (7) have strong hooks and a simple pulvillus. (X 1000). Culex (8) has fleshy pulvilli and no hooks, (x 7300) (In these scanning electron micrographs the hooks are not seen in the Aedes. The contrast between the simple pulvillus of Aedes and the fleshy pulvillus of Culex is clearly demonstra­ted.)

Tarsal claws of Aedes and Culex (2).

Photo 8. Tarsal claws of Aedes and Culex (2).

Wing scales of Culex and Mansonia.

Photo 9. Wing scales of Culex and Mansonia. The adults are distinguished from other culicines by the typical large wing scales. Culex (8); Mansonia (9). (X 370)

Wing scales of Culex and Mansonia (2).

Photo 10. Wing scales of Culex and Mansonia (2).

Peridomestic culicine breeding site near Delphi.

Photo 11. Peridomestic culicine breeding site near Delphi. Septic pits and drains containing stagnant water are ideal breeding grounds for Culex pipiens fatigans which is a peridomestic vector of bancroftian filariasis.

Male and female W. bancrofti adults.

Photo 12. Male and female W. bancrofti adults. On maturation the infective larvae copulate and the adult filariae become localised in lymph glands, eg in the groin. Adult male W. bancrofti (12) are about four cm long, females eight to 10 cm (13). (x8)

Male and female W. bancrofti adults (2)

Photo 13. Male and female W. bancrofti adults (2).

Lymphangitis.

Photo 14. Lymphangitis. Acute involvement of lymphatic vessels is common, especially in the extremities. In association with lymphangitis there is almost always some local lymphadenitis and fever.

Hydrocele.

Photo 15. Hydrocele. In the acute stages orchitis may occur. It is commonly associated with hydrocele and microfilariae may be found in the hydrocele fluid.

Elephantiasis due to B. malai.

Photo 16. Elephantiasis due to B. malai. In regions of high endemicity, lymphatic obstruction may occur, especially in the leg; progressing in chronic cases to the grotesque extreme called 'elephantiasis'. This may also arise in the arm, breast or scrotum. By this stage microfilariae are rarely found in blood films.

Elephantiasis of right epitrochlear gland in a Fijian.

Photo 17. Elephantiasis of right epitrochlear gland in a Fijian. A feature which is unusually frequent in the South Pacific and is also due to W. bancrofti is gross enlargement of the epitrochleariymph node.

lephantiasis of the scrotum due to W. bancrofti in Tahiti.

Photo 18. lephantiasis of the scrotum due to W. bancrofti in Tahiti. Severe elephantiasis of the scrotum may produce gross and incapacitating deformity that requires radical surgery to remove the surplus tissue.

Lymphogram in patient with chyluria.

Photo 19. Lymphogram in patient with chyluria. Obstruction of the cisterna chyli or its tributaries may occur. The dilated lymph vessels rupture and discharge chyle into the urinary tract, thus producing the milky appearance known as chyluria (20).

Lymphogram in patient with chyluria (chyluria ).

Photo 20. Lymphogram in patient with chyluria (chyluria ).

Microfilariae in blood films and skin snips.

Photo 21. Microfilariae in blood films and skin snips.

 If microfilariae are present in the peripheral circulation they can usually be found by examining a fresh preparation of blood taken between 10 pm and midnight. The worms may be seen in a wet preparation but morphological differentiation is only possible after suitable staining with a Romanowsky stain (Leishman or Giemsa), or haema- toxylin. W. bancrofti (21); B. malayi (22 & 23); L. loa (24 & 25); M. ozzardi (26); T. perstans (27); O. volvulus (28 & 29); T. streptocerca (30 & 31). (X 600)

Microfilariae in blood films and skin snips (2).

Photo 22. Microfilariae in blood films and skin snips (2).

Microfilariae in blood films and skin snips (3).

Photo 23. Microfilariae in blood films and skin snips (3).

Microfilariae in blood films and skin snips (4).

Photo 24. Microfilariae in blood films and skin snips (4).

Microfilariae in blood films and skin snips (5).

Photo 25. Microfilariae in blood films and skin snips (5).

Microfilariae in blood films and skin snips (6).

Photo 26. Microfilariae in blood films and skin snips (6).

Microfilariae in blood films and skin snips (7).

Photo 27. Microfilariae in blood films and skin snips (7).

Microfilariae in blood films and skin snips (8).

Photo 28. Microfilariae in blood films and skin snips (8).

Microfilariae in blood films and skin snips (9).

Photo 29. Microfilariae in blood films and skin snips (9).

Microfilariae in blood films and skin snips (10).

Photo 30. Microfilariae in blood films and skin snips (10).

Microfilariae in blood films and skin snips (11).

Photo 31. Microfilariae in blood films and skin snips (11).

Glemsa-stained microfilaria.

Photo 32. Glemsa-stained microfilaria. The sheathed microfilaria of W. bancrofti (left) is easily distinguished from that of B. malayi (right) by its size, the staining characteristics of the sheath in Giemsa stain, and the distribution of the nuclei in the posterior end. (cf 21-23) (x 350)

Microfilarial counts.

Photo 33. Microfilarial counts. Counts of microfilariae per unit quantity of blood are necessary for the epidemiological evaluation of filariasis (although not for individual diagnosis). 20 cu mm pipettes are commonly used to make a thick blood film of specified size.

Circadian rhythmm.

Photo 34. Circadian rhythmm. In a typical W. bancrofti infection parasite counts reveal a marked noc­turnal periodicity. In the diurnal subperiodic type microfilariae are readily seen in blood taken during the day.

Serological diagnosis of filariasis.

Photo 35. Serological diagnosis of filariasis. The Complement Fixation Test using Dirofilaria immitis of the dog as antigen will confirm a diagnosis of filariasis, but it does not distinguish between the different species of filaria. (Row A negative control serum; row B shows a positive titre of 1/64; row C is a negative reaction from another patient; E is complement control.)

Positive skin test with Dirofilaria antigan.

Photo 36. Positive skin test with Dirofilaria antigan. A similar antigen may also be used to demonstrate delayed cutaneous hyper­sensitivity.

Tetrapetalonema perstans.

Larvae of Culicoides.

Photo 37. Larvae of Culicoides. T. perstans is found in tropical Africa and coastal regions of Central and South America. The vectors of T. perstans are small speckled wing flies of the genus Culicoides of which C. austeni and C. grahami appear to be the main vectors in West Africa. The aquatic stages are commonly found in tree holes, leaf axils and other small natural water containers. (x 60)

Pupa of Culicoides.

Photo 38. Pupa of Culicoides.

Adult culicoides biting.

Photo 39. Adult culicoides biting.

Wing of C. grahami.

Photo 40. Wing of C. grahami.

T. persians and Loa loa in blood film.

Photo 41. T. persians and Loa loa in blood film. film The unsheathed microfilaria of T. perstans is readily distinguished from the sheathed microfilaria of Loa loa (or that of VF. bancrofti) in blood films by its smaller size, even at a fairly low magnification. Multiple infections with several species of blood-dwelling microfilariae are common. T. perstans infection is usually asymptomatic and may last many years. The adults live in body cavities, the peritoneal cavity being the commonest site. Males measure about 45 mm in length, females about 70 to 80 mm. (x 125)

See also: LoaiasisOnchocerciasis, other Filariases

 


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