Helminths

Filariae

Filariasis is one of the five major parasitic disease in world and also one of the six major tropical diseases to which WHO devotes much attention (malaria, shistosomiasis, filariasis, leishmaniasis, trypanosomiasis) . Wuchereria bancrofti and Brugia malayi are found mainly in south east asia and Africa.

Eight Species of Filariae Parasitizing Humans_____________________________________________________________________________ Species Site of inhabitation Vector Pathogenesis Distribution_______________________________________________________________________ W. bancrofti lymphatic tissues mosquito lymphatic damage worldwide____________________________________________________________________ Brugia malayi lymphatic tissues mosquito lymphatic damage Asian_______________________________________________________________________ Brugia timori lymphatic tissues mosquito lymphatic damage Island of timor ____________________________________________________________________ Onchocerca subcutaneous; eye black fly蚋 river blindness Africa volvulus_______________________________________________________________________ Loa loa subcutaneous deer fly斑虻 skin swellings Africa_______________________________________________________________________ Dipetalonema subcutaneous midge库蠓 indefinite Africa streptocerca _______________________________________________________________________ Dipetalonema thoracic and midge库蠓 indefinite Middle and perstans abdominal cavities South America_______________________________________________________________________ Mansonella peritoneal cavity midge库蠓 indefinite South America ozzardi _______________________________________________________________________

I. Morphology

Adult worm of filaria

Microfilaria of W. bancrofti and B. malayi

Microfilaria of W. bancrofti

Anterior part and posterior part of bancroftian microfilaria

Microfilaria of W. bancrofti showing it’s appearance


Bancroftian microfilaria:body nuclei equal sized, clearly, defined, countable without caudal nucleus

Microfilaria of W. bancrofti

Microfilaria of B. malayi: the body nuclei is unequal sized, coalescing,uncountable. The cephalic space is longer with two caudal nuclei.

Microfilaria of B. malayi

II. Life Cycle:
1.Biohelminth: intermediate hosts(vector) are mosquitoes, bancroftian filaria is transmitted by Culex pipiens pallens in which the larval development takes 10-14 days, the development of malayan filaria in Anopheles sinensis requires 6-6.5 days; 2. Infective stage: filariform larva(L3); 3. Infective route: by skin( the wound bitten by mosquito );

4. Site of inhabitation: lymphatic tissue; 5. Life span: 4-10 years; 6. Microfilariae may survive 1-3 months; 7. Viviparous; 8. Nocturnal periodicity: The microfilariae present in the peripheral blood during daytime is very low in density. The number of microfilariae gradually increase from evening to midnight.

Proboscis of a mosquito containing filariform larvae

A large number of 3rd stage larvae of a filarial sp emerging from the proboscis of a mosquito.



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III. Clinical manifestation

1- asymptomatic 2. Acute stage: The symptoms are due to allergic reaction. It begins with a chill followed by a high fever. It is called filarial fever. The lymphangitis, lymphadenitis may occur, orchitis and inflammation of spermatic cord are only found in infection of W. bancrofti.

3. Chronic stage obstrective: The manifestations are caused by lymphatic lesion. (1) Elephantiasis: Lymph edema may occur in the limbs, scrotum, breast, vulva and etc. (2) Chyluria only caused by W. bancrofti. (3) Hydrocele is only found in infection of W. bancrofti. 4- tropical pulmonary eiosinophillia

A patient of elephantiasis

Elephantiasis of leg due to filariasis

Elephantiasis due to Brugia malayi. Pitting does not occur in this stage (solid edema)

Elephantiasis due to Brugia malayi, complicated by severe dermatitis and secondary bacterial infection

This lady has elephantiasis of the right leg and edema in the left

Hydrocele is only found in infection of W. bancrofti.

elephantiasis of the left leg and scrotum

IV. Diagnosis

V. Treatment and Prevention

Trichinella spiralis
T.spiralis is the smallest human nematode and a biohelminth. The adults and juveniles (larvae) live in the same host, but they have to change a host to complete their life cycle.They cause trichinosis, a zoonosis, which is spread by mammals kill each other. Human infections result from eating raw meat.

I. Morphology

1. Adults: ♂1.5mm, ♀3-4mm, both have a single set of reproductive organs and stichocytes surrounding the esophagus. The secretions of stichocytes are relative to digestion and pathogenesis. 2. Juvenile: 124Ч6 µm, one or more coil in a cyst in the skeletal muscle fibers. The cyst is about 0.25-0.5 Ч0.21-0.42mm in size. This is infective stage. There are stichocytes around the esophagus.

Trichinella spiralis encysted larva

T. spralis – posterior end, male & female


II. Life cycle
1. Infective stage: juveniles in cyst 2. Site of inhabitation: adults in small intestine(mainly in duodenum and jejunum), juveniles in skeletal muscles 3. Route of infection: by mouth 4. Life span of female: 1-2 months 5. Final host and intermediate host: person 6. Reservoir host: pigs, cats, dogs, mice etc

swallowed by man digestive juice Juveniles in raw meat duodenum cysts rupture penetrate mucosa, develop and moltLarvae free from the cysts ♂adults return to intestinal lumen ♀ die Mate give birth to portal vein ♂burrow into mucosa juveniles ♀ Liver R.H lungs L. H skeletal muscle cells

III. Clinical manifestation

The process of the pathogenesis may be divided into 3 stages: 1. Invading stage(about 1 week): The damage is mainly found in the intestine. In this stage, abdominal pain, nausea,vomiting,diarrhea and fever may occur. 2. Migrating stage of the juveniles(2-3weeks):The damage is mainly in the skeletal muscles. In this stage, muscular pain with high fever is main symptoms, especially in active muscles. Wandering juveniles may also cause pneumonitis, pleurisy, encephalitis, nephritis and myocarditis etc. 3. Encysted stage(4-16 weeks): In this stage, only muscular pain present without other symptoms.

IV. Diagnosis

1. Muscular biopsy; 2. Examination of left food and xenodiagnosis; 3.Immunodiagnosis:(1) CPT(circumlarval precipitin test) (2) ELISA (3) IHA V. Treatment: Albendazole and Mebendazole VI. Epidemiology: Worldwide distribution. Lots of mammals can serve as reservoir hosts. The spread of trichinosis is due to mammals killing each other. Humans get the infection by eating raw meat. VII. Prevention 1. Quarantine of meat; 2. Avoid eating raw meat and feeding animals on raw meat.