Parasitology Lec 3.01b Blood and Tissue Nematodes

3.01

January 6, 2017

BLOOD AND TISSUE NEMATODES Dra. Nacpil

Department of Parasitology

TOPIC OUTLINE I. Filariasis a. Lymphatic Filariasis Wuchereria bancrofti Brugia malayi b. Loaiasis Loa loa c. Mansonelliasis Mansolnella ozzardi Mansonella perstans Mansonella streptocerca d. Onchocerciasis Onchocerca volvulus II. Trichinosis Trichenella III. Angiostrongyliasis Angiostrongylus IV. Toxocariasis Toxocaria V. Anisakiasis

-



 

Female worms produce microfilariae which circulate in the blood except: O. volvulus (in the skin and eye) and M. streptocerca (in the skin) Inside the arthropod, microfilariae develop in 1-2 weeks into infective filariform (3rd stage) larvae During a subsequent blood meal by the insect, the larvae infect the vertebrate host → migrate to the appropriate site and develop into adults, a slow process that can require up to one month in the case of Onchocerca

Table 2. Summary of vectors and body parts inhabited

Species W. bancrofti B. malayi

Anisakis



Causative agent: Nematodes (round worms) that inhabit the lymphatics and subcutaneous tissues 8 main species infect humans and 3 of these cause most of the morbidity due to filariasis: W. bancrofti, B. malayi and O. volvulus

Mosquitoes

O. volvulus

Blackflies (Simulium)

L. loa

Deer flies (Chrysops) Midges

FILARIASIS 

Vector

M. streptocerca M. perstans

Midges

Table 1. Geographic distribution of blood and tissue nematodes

Species Wuchereria bancrofti Brugia malayi Brugia timori Onchocerca volvulus Loa loa Mansonella streptocerca Mansonella perstans Mansonella ozzardi

   

Distribution Tropical areas Asia Islands of Indonesia Africa, Latin America, Middle East Africa Africa Africa, South America American continent

Life Cycle Infective larvae are transmitted by infected biting arthropods during blood meal Larvae migrate to the appropriate site of the host’s body, where they develop into microfilariaeproducing adults Adults dwell in various human tissues where they can live for several years. The agents of lymphatic filariasis reside in the lymphatic vessels and lymph nodes

1 of x

[E na na, what’s my name?]

M ozzardi

Midges & blackflies

Inhabited body part Lymphatic vessels and nodes Nodules in subcutaneous tissue Subcutaneous tissue Dermis and subcutaneous Body cavities and surrounding tissues Subcutaneous tissues

Lymphatic Filariasis 







Wuchereria bancrofti Mosquito vector depends on geographic distribution → most widespread filarial parasite (India, SE Asia, Pacific islands, Africa, South and Central America); Philippines: Bicol Region, Mindoro, Masbate, Romblon, Bohol, Samar, Bontoc, Sulu, Tawi-Tawi Adults produce microfilariae which are sheathed and have nocturnal periodicity (except the South Pacific microfilariae which have the absence of marked periodicity) Anopheles minimus flavirostris – principal vector for malaria in the Philippines also a vector of bancroftian filariasis in Mt. Province, Sulu, and Palawan Aedes poecilus – vector in other provinces; breeds in water accumulated in the axils of abaca and banana plants Brugia malayi

Blood and Tissue Nematodes     

Palawan, Eastern Samar, Agusan del Sur → coexists with W. bancrofti Vector is Mansonia bonnae → breeds in freshwater swamps and Mansonia uniformis → breeds in rice fields Night biters: 5-11pm; Prevalence: 3% Cats are important reservoir host & transmit infection to humans by means of catmosquito-man cycle There are two strains of B. malayi: 1. Nocturnal periodic strain – widely distributed in Asia, the microfilariae being in their highest concentrations between 10pm to 2am 2. Subperiodic strain – in Malaysia, Indonesia and Philippines where humans exhibit a microfilaremia all the time with the highest numbers being detected between noon and 8pm

Life Cycle (W. bancrofti and B. malayi) DIAGNOSTIC: microfilariae INFECTIVE: 3rd stage filarial larvae

 

 

A mosquito ingests the microfilariae during a blood meal (4). After ingestion, the microfilariae lose their sheaths and some of them work their way through the wall of the proventriculus and cardiac portion of the mosquito’s midgut and reach the thoracic muscles (5). There the microfilariae develop into 1st stage larvae (6) and subsequently into 3rd stage infective larvae (7). The 3rd stage infective larvae migrate through the hemocoel to the mosquito’s proboscis (8) and can infect another human when the mosquito takes a blood meal.

Term

Disease caused

Vectors

Figure 1. Life cycle of W. bancrofti and B. malayi



 

During a blood meal, an infected mosquito introduces 3rd stage filarial larvae onto the skin of the human host, where they penetrate into the bite wound (1). They develop in adults that commonly reside in the lymphatics (2). The microfilariae migrate into lymph and blood channels moving actively through lymph and blood (3).

Developm ent of microfilari ae → infective stage Mean length Cephalic space (breadth) Sheath in Giemsa Nuclei Tail

2 of x

[E na na, what’s my name?]

Parasite Biology W. bancrofti B. malayi FILARIAL WORM Bancroft’s filarial Malayan worm filarial worm Bancroftian Malayan filariasis → chronic filariasis → disfugring disease chronic → lymphedema, infection also elephantiasis, presents with hydrocele, chronic lymphedema epididymis, and thickening of elephantiasis spermatic cord but not as severe; enlargement of epitrochlear, inguinal, axillary lymph nodes Aedes, Culex, Mansonia Anopheles 6-20 days 2 weeks; maturation time for 3rd stage larvae → adult is 3-9 months 290µm 222µm 1:1

2:1

Unstained

Pink

Regularly spaced, separately situated

Irregularly spaced and overlapping Single row of

Single row of

Blood and Tissue Nematodes

Terminal Nuclei

Appearan ce in blood film Male Female

Length Appearan ce

  

nuclei that does not reach the tail’s ends None

Smoothly curved ADULT 2-4 cm 8-10 cm – creamy white, long, filiform in shape MICROFILARIA 270-290µm by 67µm Enclosed in hyaline sheath longer than the microfilariae itself; nocturnal periodicity; central axis is seen as composed of dark staining nuclei; column of nuclei are in 2-3 rows and are distinctly conspicuous; has several curvatures; microfilaria appears snake-like in fresh specimens among RBC

nuclei that reaches the tail’s ends 2 nuclei which bulge the cuticle, conspicuousl y placed Kinky

 

13-23 mm 43-55 mm

177-230µm Enclosed in sheath; has angular curvatures with secondary kinks; has 2 nuclei at the tip of the tail; column are in 2 rows which are indistinct or confluent

Clinical Manifestations Lymphatic filariasis most often consists of asymptomatic microfilaremia Development of lymphatic dysfunction causing lymphedema and elephantiasis With W. bancrofti, there is hydrocele & scrotal elephantiasis

3 of x



[E na na, what’s my name?]

  

Febrile lymphangitis and lymphadenitis may occur Persons who have newly arrived in diseaseendemic areas can develop afebrile episodes of lymphangitis & lymphadenitis Tropical Pulmonary Eosinophilia Syndrome (TPE) o An additional manifestation of filarial infection, mostly in Asia o Immunologic hyperresponsiveness to filarial infection o Characterized by nocturnal cough, wheezing, fever, and eosinophilia, diffuse military lesions or increased vascular markings, high titers filarial antibody (IgE, good therapeutic response to Diethylcarbamazine citrate); can progress to pulmonary fibrosis and respiratory failure In endemic countries, symptoms may overlap Microfilariae → less pathology associated with TPE, granulomas of the skin, allergic reactions following destruction by drugs Expatriate Syndrome – those who are infected after migration to endemic regions present with this syndrome; clinical and immunologic hyperresponsiveness to the mature or maturing worms; presents with lymphadenitis and lymphangitis with allergic reactions such as hives, rashes, and blood eosinophilia

I. ASYMPTOMATIC STAGE  Presence of thousands to millions of microfilariae in the peripheral blood and adult worms in the lymphatic system with no manifestations of filariasis  Seen among those with highly down regulated immune state  May have hidden lymphatic pathology and kidney damage  Brugia can selectively induce CD4+ lymphocyte apoptosis which contributes to immune system unresponsiveness to filariasis  Also seen in ‘endemic normals’ who harbor the parasite antigen in their blood instead of the microfilariae II. ACUTE STAGE  Early manifestations: fever, inflammation of the lymph glands (especially of the male genital organs, arms, and legs)  Recurrent attacks: swelling and redness of the arms and legs, accompanied by vomiting and headache

Blood and Tissue Nematodes 

S/sx reflect immunologic phenomenon caused by sensitization to the products of living or dead worms collectively called adenolymphangitis (ADL) or dermatolymphangioadenitis (DLA)

III. CHRONIC STAGE  With repeated acute episodes, acute manifestations merge into a chronic proliferative overgrowth of fibrous tissue around the dead worms → lymphatic obstruction, recurrent attacks of DLA and lymphedema, elephantiasis or hydrocele  Cellular reaction and edema are replaced by fibrous hyperplasia (parasite absorbed and replaced by granulation tissue, while lymph varices are produced; increased lymphatic fluid pressure and high protein content of lymph stimulate growth of dermal and collagenous tissue elephantiasis (hard, loss of skin elasticity, fibrosis)  Develops slowly: chronic pitting edema, chronic nonpitting, edema with repeated acute inflammatory episodes o Lymphedema: 6 months; Elephantiasis: 1 year  In endemic communities – different stages overlap  Manifestations are caused by adult worms, living, dead, or degenerating  Microfilariae cause less pathology but have been associated with: TPE, skin granulomas, allergic reactions following destruction by drugs

Fig. 3. Wuchereria scrotum

Wuchereria scrotum – worms in scrotal lymphatics stimulates proliferation of lymphatic endothelium and accumulation of hydrocele fluid Chyluria – rupture of lymphatics in the kidney due to blockage of retroperitoneal lymph nodes; several reports of glomerulonephritis in bancroftian filariasis

Loaisis    

Loa loa African eye worm: Sudan rainforest, basin of Congo and W. Africa Causes Loaisis: similar to onchocerciasis and can cause blindness Migrates throughout subcutaneous tissues of the body Most conspicuous and irritating when crossing the conjunctiva

Fig.4 L. loa microfilariae (L) and its vector, Chrysops (R )

  Fig. 2. Wuchereria elephant foot

Wuchereria Elephant foot – increased lymphatic fluid pressure and high protein content of lymph stimulate growth of collagenous CT; enlarge parts hidden with loss of skin elasticity and fibrosis producing elephantiasis







Vectors: Chrysops silacea and C. dimidata (deerflies), both are day-biting flies Adult males: 2-3.5 cm long ; Adult females: 57cm long Microfiariae: 250-300 um long, sheathed and have body nuclei that are continuous to the tip of the tail (difference to that of Wuchereria’s & Brugia’s microfilariae Microfilariae has diurnal periodicity o During the day → peripheral blood o During the non-circulation phase → lungs Microfilariae have been recovered from spinal fluids, urine, and sputum Life Cycle

4 of x

[E na na, what’s my name?]

Blood and Tissue Nematodes DIAGNOSTIC: microfilariae INFECTIVE: 3rd stage filarial larvae 

 

 

 

     

During a blood meal, an infected fly introduces 3rd stage filarial larvae onto the skin of the human host, where they penetrate into the bite wound (1). The larvae develop into adults that commonly reside in subcutaneous tissue (2). Adults produce microfilariae that are found in peripheral blood during the day but during the non-circulation phase, are found in the lungs (3). The fly ingests microfilariae during a blood meal (4). After ingestion, the microfilariae lose their sheaths and migrate from the fly’s midgut through the hemocoel to the thoracic muscles of the arthropod (5). There the microfilariae develop into 1st stage larvae (6) and subsequently into 3rd stage infective larvae (7). The 3rd stage infective larvae migrate to the fly’s proboscis (8) and can infect another human when the fly takes a blood meal (1). Clinical Manifestations Often asymptomatic Episodic angioedema & subconjunctival migration of an adult worm can occur Non painful migration through tissues Conjunctival edema Calabar swelling – patches of localized subcutaneous edema Eosinophilia

Fig. 5. Calabar swelling (L) and may lead to progressive keratitis (R )

Mansonelliasis Mansonella M. ozzardi M. perstans Vecto r

Midges (Culicoides) or Black flies (Simulium)

Midges (Culicoides)

Adult s

Females: 65- 81 mm in length and 0.21 to 0.25 mm in diameter Males: unknown

Females:70 80 mm in length and 120 µm in diameter

Females: 27 mm in length by 50 -85 µm

Males: 45 mm by 60 µm. Deep connective tissue

Males: 50 µm

Unsheathed

Unsheath ed

No periodicity (Doc Nacpil); Weak diurnal periodicity (Doc Malijan)

No periodicit y (Doc Nacpil); Weak diurnal periodicit y (Doc Malijan) Nuclei extend to the tip of the tail which is bent in the form of a shepher d’s crook

Microfilaria e Perio di-city

Tail

Clinic al

5 of x

[E na na, what’s my name?]

M. streptoc erca Small midges (Culicoid es)

Inhabit mesenterie s and visceral fat Unsheathe d No periodicity

Nuclei do Nuclei not extend extend until to the tip of the tip of the the tail and tail tail is shorter and less tapered than Onchocerc a ; button hook Found in the blood; may be obtained by skin biopsy Generally Often Skin asymptoma asymptomati manifest

Blood and Tissue Nematodes Manif estati ons

tic, inguinal adenopathy has been reported, skin lesions, arthritis, fever, marked eosinophilia and pulmonary symptoms, adenopathy , hepatomeg aly, pruritus

c, associated angioedema, pruritus, fever, headaches, arthralgias, and neurologic manifestatio ns; edema and inflammatory changes and granulomas from around dead filariae; marked eosinophilia

ations including pruritus, popular eruptions and pigmenta tion changes

   

Life Cycle DIAGNOSTIC: microfilariae INFECTIVE: 3rd stage larvae 

Life Cycle DIAGNOSTIC: microfilariae INFECTIVE: 3rd stage larvae









  

 

During a blood meal, the infected vector introduces 3rd stage filarial larvae onto the skin of the human host, where they penetrate into the bite wound (1). The larvae develop into adults that commonly reside in the subcutaneous tissue (M. ozzardi), peritoneal or pleural cavity (M. perstans), dermis (M. streptocerca) (2). Adults produce unsheathed and nonperiodic microfilariae that reach the bloodstream (3). A vector ingests microfilariae during a blood meal (4). After ingestion, the microfilariae lose their sheaths and migrate from the fly’s midgut through the hemocoel to the thoracic muscles of the arthropod (5). There the microfilariae develop into 1st stage larvae (6) and subsequently into 3rd stage infective larvae (7). The 3rd stage infective larvae migrate to the fly’s proboscis (8) and can infect another human when the midge takes a blood meal (1).

Onchocerciasis  

Onchocerca volvulus Causes onchocerciasis or river blindness which is a major cause of blindness in some parts of Africa Vector: black fly (Simulium)

6 of x

[E na na, what’s my name?]

Adult worms: wire-like, whitish, lie coiled within fibrous tissue capsules o Females: 50cm; Males: 5cm Microfilariae: unsheathed – 15-350µm; often found in the skin rarely in urine, blood, and sputum Developing worms wander through subcutaneous tissues Most worms become encapsulated – nodules are produced

   

 

During a blood meal, an infected blackfly (Simulium) introduces 3rd stage filarial larvae onto the skin of the human host, where they penetrate into the bite wound (1). In the subcutaneous tissues the larvae (2) develop into the adult filariae, which commonly reside in the nodules of the subcutaneous tissue (3). Adults can live for approximately 15 years. Some nodules may contain numerous male and female worms. In the subcutaneous nodules, the female worms are capable of producing microfilariae for approximately 9 years. (4). A black fly ingests the microfilariae during a blood meal (5). After ingestion, the microfilariae migrate from the blackfly’s midgut through the hemocoel to thoracic muscles (6). There the microfilariae develop into 1st stage larvae (7) and subsequently into 3rd stage infective larvae (8). The 3rd stage infective larvae migrate to the fly’s proboscis (9) and can infect another human when the vector takes a blood meal (1). Clinical Manifestations Onchocerciasis can cause pruritus, dermatitis, onchocercoma or sowda (subcutaneous nodules)& lymphadenopathies The most serious manifestation consists of ocular lesions that can progress to blindness

Blood and Tissue Nematodes 

Fig. 6. Onchocercoma (L) and river blindness (R )

Review: Filariasis = Lymphatic Filariasis ,Loaisis ,Mansonelliasis ,Onchocerciasis

Generalities of Filariasis Periodicity Fluctuations in numbers of microfilariae present in the peripheral blood during a 24hour period



Table 3. Periodicity of filariasis

Periodici ty Nocturn ally periodic Diurnally periodic Nonperi odic or aperiodi c

Subperio dic

1.

Definition Species found in the blood during night time hours but absent at other times Present only during certain daytime hours Microfilariae that circulate in the blood throughout a 24 hour period without significant changes in their numbers Microfilariae normally present in the blood at all hours but whose density increases significantly during either the night or day

Example s W. bancrofti and B. malayi Loa loa

[E na na, what’s my name?]



Mansonia spp.  B. malayi

Diagnosis Examination of blood samples to identify microfilariae

7 of x

Blood samples can be a thick smear, stained with Giemsa or H&E  For increased sensitivity, concentration techniques can be used : o Centrifugation of the blood sample lyzed in 2% formalin (Knott’s technique), or filtration through a Nucleopore® membrane  Examination of skin snips will identify microfilariae of Onchocerca volvulus and Mansonella streptocerca o Skin snips are obtained using a cornealscleral punch, or a scalpel & needle o Allow sample to incubate for 30 minutes to 2 hours in saline or culture medium, and then examined for microfilariae that would have migrated from the tissue to the liquid phase of the specimen 2. Finding of microfilariae in the blood as seen in wet or thick blood smears taken between 8pm and 4am  W. bancrofti microfilariae – nocturnal periodicity  B. malayi microfilariae – Subperiodic periodicity  In low intensity infection, Knott’s method for concentration may be used  DEC (Diethylcarbamazepine) provocative test stimulates microfilariae to come out to peripheral circulation allowing blood smear collection even during daytime 3. Antigen detection techniques to detect circulating filarial antigens (CFA) – useful in low and variable infection





Diagnostic Findings Antigen detection using an immunoassay for circulating filarial antigens – useful because microfilaremia can be low and variable o A rapid-format immunochromatographic test, applicable to W. bancrofti antigens, has been recently evaluated in the field Molecular diagnosis using PCR is available for W. bancrofti & B. malayi Antibody detection has limited value o Substantial antigenic cross reactivity exists between filarial and other helminths, and a positive serologic test does not distinguish between past and current infections Identification of adult worms is possible from tissue samples collected during nodulectomies (Onchocerciasis), or during subcutaneous biopsies or worm removal from the eye (Loaiasis)

Blood and Tissue Nematodes







 



 

 

Special Procedures for Detecting Blood Microfilariae Capillary (fingerstick) blood o Since microfilariae concentrate in the peripheral capillaries, thick and thin smears prepared from fingerstick blood are recommended Anticoagulated (EDTA) venous blood (1ml) should be concentrated by one of the following methods o Centrifugation (Knott’s technique) – uses 2% formaldehyde o Filtration – uses membrane filter (Millipore® or Nucleopore® membrane filter) Ultrasonography, contrast lymphangiography, lymphscintigraphy o May demonstrate live worms in the lymphatics Treatment Different drugs are recommended for the treatment of filariasis depending on the specific causal agent Diethylcarbamazine citrate (DEC) – DRUG OF CHOICE o Bancroftian filariasis – 6 mL/day orally for 12 days (given in divided doses after meals) o Brugian filariasis – 3 to 6 mg per kg per day up to 36 to 72 mg/bw Ivermectin – 200 to 400 µg/kg single oral dose = as effective as 12 days of DEC Prevention and Control Goal for endemic communities: Eliminate microfilariae in the blood to prevent transmission of disease by vectors Control of transmission: o Identification of endemic areas o Implementation of mass treatment programs using Albendazole/DEC or DEC/Ivermectin combination in areas where onchocercosis or loaiasis is prevalent Personal protective measures Vector control: Development of sprays and polyester beads to seal latrines

TRICHINOSIS/TRICHENELLOSIS 

Trichenella In addition to the classical agent T. spiralis (found worldwide in many carnivorous and omnivorous animals), several other species of Trichinella are now recognized:

8 of x

[E na na, what’s my name?]

o o o o

T. pseudospiralis (mammals and birds worldwide) T. nativa (Arctic bears) T. nelson (African predators and scavengers) T. britovi (carnivores of Europe and western Asia)

Table 4. Different forms of Trichenella

Form Female adult

Male adult

Larva

Description 2.2 mm in length (3.5 mm by 0.06 mm) Single ovary in the posterior part of the body ; Has oviduct, seminal receptacle, coiled uterus, vagina and vulva in the anterior 5th on the ventral side of the body; Viviparous females (life span: 30 days) can produce > 1500 larvae Approximately 1.2 mm, Single testis located near the posterior end and is joined in the mid-body by the genital tube, which in turn extends back to the cloaca; Cloaca has a pair of caudal appendages and 2 pairs of papillae 80 – 120 µm by 5.6 µm at birth; Has a spear like burrowing anterior tip; Infective larvae are encysted in the muscle fiber of the host – this is used as a diagnosis through biopsy or autopsy specimens

Life Cycle DIAGNOSTIC: encysted larvae in striated muscle INFECTIVE: encysted larvae

Blood and Tissue Nematodes 





 Figure 7. Life cycle of Trichenella

 

  





 

Trichinellosis is acquired by ingesting meat containing cysts (encysted larvae) (1) of Trichinella. After exposure to gastric acid and pepsin, the larvae are released (2) from the cysts and invade the small bowel mucosa where they develop into adult worms (3). After 1 week, the females release larvae (4) that migrate to the striated muscles where they encyst (5). Trichinella pseudospiralis, however, does not encyst. Encystment is completed in 4-5 weeks and the encysted larvae may remain viable for several years. Ingestion of the encysted larvae perpetuates the cycle. Rats and rodents are primarily responsible for maintaining the endemicity of this infection. Carnivorous/omnivorous animals, such as pigs or bears feed on infected rodents or meat from other animals. Humans are accidentally infected when eating improperly processed meat of these carnivorous animals (or eating food contaminated with such meat). Clinical Manifestations Light infections may be asymptomatic Intestinal invasion is accompanied by GI symptoms: o Diarrhea, abdominal pain, vomiting

9 of x

[E na na, what’s my name?]

 

Larval migration into muscle tissues (one week after infection) can cause o Periorbital and facial edema, conjunctivitis, fever, myalgias, splinter hemorrhages, rashes, and blood eosinophilia Occasional life-threatening manifestations: o Myocarditis, central nervous system involvement, and pneumonitis o Larval encystment in the muscles causes myalgia and weakness, followed by subsidence of symptoms. Severity of symptoms depend on intensity of infection o Light infection: patients harboring up to 10 larvae o Moderate infection: 50-500 worms o Severe and potentially fatal: > 1,000 larvae Full recovery expected since it’s a self-limiting disease Complications: myocardial and neurologic Prognosis is good in mild infections o Death is uncommon except in cases with complications (heart failure, encephalitis, pneumonia, sepsis) o Low-grade or absent peripheral blood eosinophila – poor prognosis

Table 5. Phases of Clinical Conditions

Phase Enteric

Invasio n

Conval escent

 

Description Stage of incubation and intestinal invasion Larval migration & muscle invasion

Encystment and encapsulation

S/Sx Diarrhea or constipation, vomiting, cramps, malaise, nausea Myalgia, periorbital edema & eosinophilia – cardinal signs and symptoms; Also high remittent fever, dyspnea, dysphagia, difficulty chewing, paralysis of extremities, GI hemorrhage, splenomegaly Abatement of fever, pain, weakness and other symptoms

Diagnosis Based on Hx of exposure and PE Most definitive diagnostic exam demonstration of larva using muscle biopsy

Blood and Tissue Nematodes    

 

 

Biochemical test: elevated CPK, LDH and myokinase High blood count and peripheral eosinophilia – strengthen diagnosis Serology may provide confirmatory diagnosis Beck’s xenodiagnoses: when meat is suspected on harboring encysted larva o Feeding the meat to albino rats; observe them 14 days after for female worm in the duodenum and larvae in the muscles of experimental host Suspicion of trichinellosis (trichinosis) based on clinical symptoms and eosinophilia Can be confirmed by specific diagnostic tests: antibody detection, muscle biopsy and microscopy Treatment Should begin as soon as possible Bed rest, supportive treatment

Table 6. Treatment for Trichinella infection

Drug Thiabenda zole

Mebendaz ole Albendazo le Steroids

  

Description 25 mg/kg 2x/d for 7d Expels adult worm from GIT during 1st week of infection; Has no effect on migrating larvae and is useless for infections detected two weeks after exposure Larvicidal when given at 20mg/kg every 6hrs for 10-14 days Shows promise but has not yet been sufficiently evaluated Used for infections with severe symptoms; Prednisone 20mg 3x daily tapered over 2-3 weeks

Epidemiology Occurs whenever meat is part of the diet Humans get infected after ingestion of raw or insufficiently cooked meat of infected animals. Infection is maintained in a pig-to-pig or pigto-rat-to-pig cycle Prevention and Control

  

Health education



Smoking, salting, drying – not effective

Cook meat 77°C Freezing at -15°C for 20 days or -30°C for six days can kill the larvae

10 of x

[E na na, what’s my name?]



Meat inspection and keeping pigs in rat-free pens

ANGIOSTRONGYLIASIS Causal agents:  Angiostrongylus cantonensis (rat lungworm) = Human Eosinophilic Meningitis  Angiostrongylus (Parastrongylus) costaricensis = Abdominal or Intestinal Angiostrongyliasis Angiostrongylus cantonensis Form Description Female 21-25 mm by 0.30 -0.36 mm; adult Has uterine tubules which are wound spirally around the intestine; BARBER’S POLE pattern; Lays up to 15000 eggs/day Male 16 – 19 mm by 0.26 mm; adult Well-developed caudal bursa which is kidney shaped and single lobed Life Cycle INFECTIVE to intermediate host: 1st stage larvae INTERMEDIATE HOST: Snails or slugs INFECTIVE to definitive host: 3rd stage larvae DEFINITIVE HOST: Rats and rodents INCIDENTAL HOSTS: Humans

Blood and Tissue Nematodes Figure 8. Life cycle of Angiostrongylus cantonensis

 

  











 



Adult worms of A. cantonensis live in the pulmonary arteries of rats The females lay eggs that hatch, yielding 1st stage larvae, in the terminal branches of the pulmonary arteries. The 1st stage larvae migrate to the pharynx, are swallowed, and passed in the feces. They penetrate, or are ingested by, an intermediate host (snail or slug). After two molts, 3rd stage larvae are produced, which are infective to mammalian hosts. When the mollusk is ingested by the definitive host, the 3rd stage larvae migrate to the brain where they develop into young adults. The young adults return to the venous system and then the pulmonary arteries where they become sexually mature.

 

Known intermediate hosts in the Philippines: o Slugs and snails o Achatina fulica o Hemiplecta sagittifera o Helicostyla macrostoma o Vaginilus plebeius o Veronicella altae o The African Giant Snail



Many animals act as paratenic (transport) hosts: after ingesting the infected snails, they carry the 3rd stage larvae which can resume their development when the paratenic host is ingested by a definitive host. Humans acquire the infection by eating raw or undercooked snails or slugs, vegetables contaminated with mollusks secretions, or infected paratenic animals (crabs, freshwater shrimps) o Development of the 3rd stage larvae is stalled in the brain, where they die In humans, juvenile worms migrate to the brain, or rarely in the lungs, where the worms ultimately die The life cycle of Angiostrongylus (Parastrongylus) costaricensis is similar, except that the adult worms reside in the arterioles of the ileocecal area of the definitive host In humans, A. costaricensis often reaches sexual maturity and release eggs into the intestinal tissues. The eggs and larvae degenerate and cause intense local inflammatory reactions and do not appear to be shed in the stool

11 of x

[E na na, what’s my name?]

 

   

      







Clinical Manifestations Incubation period is usually between 6-15 days Intermittent occipital or bitemporal headache is often the chief complaint Eye involvement: hemorrhage & retinal detachment Clinical symptoms of eosinophilic meningitis are caused by the presence of larvae in the brain and by local host reactions o Severe headaches, nausea, vomiting, neck stiffness, seizures, and neurologic abnormalities may occur Occasionally, ocular invasion may be present Eosinophilia is observed in most of cases Most patients recover fully Abdominal angiostrongyliasis mimics appendicitis, with eosinophilia Diagnosis In eosinophilic meningitis the cerebrospinal fluid (CSF) is abnormal (elevated pressure, proteins, and leukocytes; eosinophilia). On rare occasions, larvae have been found in the CSF. CT scans – may show meningeal lesions Serologic confirmation - ELISA In abdominal angiostrongyliasis, eggs and larvae can be identified in the tissues removed at surgery Presumptive diagnosis is made by travel and exposure history In humans, eggs and larva are not normally excreted but remain sequestered in tissues. Both eggs and larvae (occasionally adult worms) of A. costaricensis can be identified in biopsy or surgical specimens of intestinal tissues. The larvae need to be distinguished from larvae of Strongyloides stercoralis, however, the presence of granulomas containing thin shelled eggs and/or larvae serve to distinguish A. costaricensis infections. Treatment No antihelminthic treatment is recommended at present although mebendazole, thiabendazole albendazole and ivermectin were found to be successful in animal experiments Antihelminthics are usually not necessary because the disease is self-limiting and killing the worms may bring about greater inflammatory reactions Analgesics; removal of spinal fluid at regular intervals can relieve headache

Blood and Tissue Nematodes     

Prednisone 30mg daily: recommended in severe cases with cranial nerve involvement Surgical removal: when parasite is lodged in the anterior chamber of the eye Prognosis is usually good Infection is self-limiting, complete recovery usually occurs Permanent neurologic deficits do occur and may occasionally be fatal

DEFINITIVE HOSTS: Dogs ACCIDENTAL HOSTS: Humans 

 

TOXOCARIASIS   

  

 

   

Toxocara canis Toxocariasis is caused by the larvae of Toxocara canis (dog roundworm) and less frequently of T. cati (cat roundworm) Accomplishes its life cycle in dogs, with humans acquiring the infection as accidental hosts Puppies are infected with T. canis as early as the fetal stage or at birth due to transplacental and transmammary transmission (important source of eggs) Man becomes infected by ingestion of embryonated eggs through contaminated food and water Other mammals and birds may serve as paratenic hosts This disease occurs worldwide Parasite Biology Males, 4-6 cm long, are smaller than females. The male's posterior end is curved ventrally and the tail is bluntly pointed. The female worms are generally around 6.5 cm but can be as long as 15 cm long. Egg contains a well-developed larvae ; this will be infective if ingested by a human (frequently, a child). These eggs are passed in dog feces, especially in puppies Human infections do not produce or excrete eggs, and therefore eggs are not a diagnostic finding in human toxocariasis

Fig. 10. Life cycle of Toxocara canis



 Fig. 9. Toxocara canis larva hatching

Life Cycle INFECTIVE : Embryonated eggs with larvae

12 of x

[E na na, what’s my name?]

T. canis accomplishes its life cycle in dogs, with humans acquiring the infection as accidental hosts. Unembryonated eggs are shed in the feces of the definitive host (1). Eggs embryonate and become infective in the environment (2). Following ingestion by dogs (3), the infective eggs hatch and larvae penetrate the gut wall. In younger dogs, the larvae migrate through the lungs, bronchial tree, and esophagus; adult worms develop and oviposit in the small intestine (4).

In older dogs, patent infections can also occur, but larval encystment in tissues is more common. Encysted stages are reactivated in female dogs during late pregnancy and infect by the transplacental and transmammary routes the puppies (5), in whose small intestine adult worms become established (6). Puppies are a major source of environmental egg contamination. Toxocara canis can also be transmitted through ingestion of paratenic hosts: eggs ingested by small mammals (rabbits) hatch and larvae penetrate the gut

Blood and Tissue Nematodes

 





 

wall and migrate into various tissues where they encyst (7). The life cycle is completed when dogs eat these hosts (8) and the larvae develop into egg-laying adult worms in the small intestine. Humans are accidental hosts who become infected by ingesting infective eggs in contaminated soil (9) or infected paratenic hosts (10). After ingestion, the eggs hatch and larvae penetrate the intestinal wall and are carried by the circulation to a wide variety of tissues (liver, lungs, brain, muscle, eyes) (11). While the larvae do not undergo any further development in these sites, they can cause severe local reactions that are the basis or Toxocarasis. Clinical Manifestations Many human infections are asymptomatic, with only eosinophilia and positive serology as the only indications of infection Death can occur rarely, by severe cardiac, pulmonary, or neurologic involvement

Table 7. Two main clinical manifestations

Disease Viscera l larva migran s (VLM)

Ocular larva migran s (OLM)



Description Larvae invade multiple tissues (liver, heart, lungs, brain, muscle) and cause various symptoms

Larvae produce various ophthalmologic lesions, which in some cases have been misdiagnosed as retinoblastoma, resulting in surgical enucleation

S/Sx Fever, anorexia, weight loss, cough, wheezing, rashes, hepatosplenom egalyand hypereosinophil ia ; Occurs mostly in preschool children Often occurs in older children or young adults, with only rare eosinophilia or visceral manifestations

Diagnosis Diagnosis does not rest on identification of the parasite

13 of x

[E na na, what’s my name?]









 

Since the larvae do not develop into adults in humans, a stool examination would not detect any Toxocara eggs o Presence of Ascaris and Trichiuris eggs in feces, indicating fecal exposure, increases the probability of Toxocara in the tissues For both VLM and OLM, a presumptive diagnosis rests on clinical signs, history of exposure to puppies, laboratory findings (including eosinophilia), and the detection of antibodies to Toxocara Antibody Detection: The only means of confirmation of a clinical diagnosis of visceral larva migrans (VLM), ocular larva migrans (OLM), and covert toxocariasis (CT), o The currently recommended serologic test for toxocariasis is enzyme immunoassay (EIA) Toxocara excretory-secretory (TES) antigens are preferable to larval extracts because they are convenient to produce and because an absorption-purification step is not required for obtaining maximum specificity Treatment VLM: treated with antiparasitic drugs, usually in combination with anti-inflammatory medications OLM: more difficult to treat and usually consists of measures to prevent progressive damage to the eye. o Albendazole, Mebendazole

ANISAKIASIS  

  

  

Anisakis Caused by the accidental ingestion of the larve of Anisakis simplex and Pseudoterranova decipiens Larval stages of anisakine nematodes persist in the alimentary canal or penetrating the tissues of humans after consuming raw or semi-raw fish, as in sushi Fish species acts as intermediate/transport hosts for the larva Larva matures into adults in warm-blooded marine mammals No human case yet reported in the Philippines but the potential for infection is great Parasite Biology Has a pseudocoel Complete digestive system Cuticle has 3 main layers and shed 4 times during their life cycle

Blood and Tissue Nematodes  

Length: 5-30 mm Sexual dimorphism: females are larger Life Cycle





  

 

Fig. 11. Life cycle of Anisakis simplex



   

  

Adult stages of Anisakis simplex or Pseudoterranova decipiens reside in the stomach of marine mammals, where they are embedded in the mucosa, in clusters. Unembryonated eggs produced by adult females are passed in the feces of marine mammals . The eggs become embryonated in water, and first-stage larvae are formed in the eggs. The larvae molt, becoming second-stage larvae , and after the larvae hatch from the eggs, they become free-swimming . Larvae released from the eggs are ingested by crustaceans . The ingested larvae develop into third-stage larvae that are infective to fish and squid . The larvae migrate from the intestine to the tissues in the peritoneal cavity and grow up to 3 cm in length. Upon the host's death, larvae migrate to the muscle tissues, and through predation, the larvae are transferred from fish to fish. Fish and squid maintain third-stage larvae that are infective to humans and marine mammals . When fish or squid containing

14 of x

[E na na, what’s my name?]

 

third-stage larvae are ingested by marine mammals, the larvae molt twice and develop into adult worms. The adult females produce eggs that are shed by marine mammals . Humans become infected by eating raw or undercooked infected marine fish After ingestion, the anisakid larvae penetrate the gastric and intestinal mucosa, causing the symptoms of anisakiasis. Clinical Manifestations Within hours after ingestion of infected larvae, violent abdominal pain, nausea, and vomiting may occur. Occasionally the larvae are coughed up If the larvae pass into the bowel, a severe eosinophilic granulomatous response may also occur 1 to 2 weeks following infection, causing symptoms mimicking Crohn's disease Diagnosis Diagnosis can be made by gastroscopic examination during which the 2 cm larvae are visualized and removed Histopathologic examination of tissue removed at biopsy or during surgery Treatment, Prevention & Control The treatment of choice is surgical or endoscopic removal Avoid ingestion of raw or undercooked seafood

Fig. 12. Fish with Anasakis





Epidemiology Found worldwide, with higher incidence in areas where raw fish is eaten (e.g., Japan, Pacific coast of South America, the Netherlands). Increasing incidence in the US due to increased consumption or raw fish.

MORE MORE MORE…………… Appendix A. Comparison of microfilariae sizes and morphology from Dr. Nacpil’s ppt

Blood and Tissue Nematodes Species W. bancrofti

Morphology Sheathed, Tail pointed and clear

B. malayi

Sheathed, Tail pointed with 2 nuclei

L. loa M. ozzardi M. perstans

Geographi cal distributio n Vectors

Microfilariae size 210- 320 µm By 8-10 µm 170-260 µm By 5-6 µm 230 – 300 µm By 6-8 µm 250 µm by 6-7 µm 200 µm by 6 µm W. bancrofti B. malayi B. timori

Tropics and subtropics worldwide

South East Asia; Indian subcontinent

Mosquitoes: Culex, Aedes, Anopheles, Mansonia Lymphatic system

Mosquitoes: Aedes, Anopheles, Mansonia Lymphatic system

Microfilari ae habitat

Blood

Periodicity

Sheathed, Tail blunt with nuclei Unsheathed, Tail pointed and clear Unsheathed, Tail blunt with nuclei L. loa M. ozzardi

M. perstans

Indonesian archipelago, Timor, Lesser Sunda Mosquitoes: Anopheles

West and Central Africa

Caribbean, Central and South America

Africa and South America

Tabanid flies; deer flies (Chrysops)

Biting midges (Culicoides)

Lymphatic system

Subcutaneous tissue, conjunctiva

Biting midges (Culicoides), black flies (Simulium) Subcutaneous tissue

Blood

Blood

Blood

Blood

Mesenteries, connective tissue of abdominal organs Blood

Nocturnal

Nocturnal

Nocturnal

Diurnal

Aperiodic

Aperiodic

Sheath

Present

Present

Present

Present

Absent

Absent

Width (µm)

7.5-10

5.0-6.0

4.5-6.0

5.0-7.0

3.0-5.0

4.0-5.0

Tail

Tapered, anucleate

Tapered; nuclei irregularly spaced to end of tail Single row of nuclei to end of tail, sheath unstained in Giemsa

Bluntly rounded nuclei to end of tail

Short head space, dispersed nuclei, sheath unstained in Giemsa, body in smooth curves

Tapered; subterminal and terminal nuclei widely separated Long head space, sheath unstained in Giemsa, terminal and subterminal nuclei

Long, slender, pointed, anucleated

Key features of microfilari ae

Tapered; subterminal and terminal nuclei widely separated Long head space, sheath stains in Giemsa, terminal and subterminal nuclei

Small size, long slender tail, aperiodic

Small size, blunt tail filled nuclei, aperiodic

Adult habitat

Summary from Dra. Nacpil’s ppt 

15 of x

[E na na, what’s my name?]