Filariasis

Question 1

What are some filarial infections?

Answer 1

Lymphatic filariasis
- Caused by parasite Wuchereria bancrofti - typical of this is a sheath around larva
- Brugia timori/Brugia malayi

Loaiasis (eye worm)
- Caused by loa loa

Onchocerciasis (blinding worm)
- Onchocerca volvulus – causes river blindness

Others
- Mansonelliasis
- Mansonella perstans/M. streptocerca/M. Ozzardi

Question 2

Life cycle

Answer 2

Transmitted by mosquito vector

Bites and in saliva the L3 Larvae are transmitted into the skin

Larvae will migrate and develop into adults, live in lymphatics

Populate and the female produces sheath like filaria into circulation, found in lymphatics and blood

Mosquito takes up the filaria in the blood and undergoes further development

Question 3

What are parasites?

Answer 3

White, slender, roundworms

Three types: Wuchereria bancrofti, Brugia malayi, Brugio timori

Live for 5-7 years in lymphatics, female adult produce millions of offspring

Adults block the lymphatic system
- Network of channels and lymph nodes that help maintain fluid levels in the body
- Blockage leads to edema (collection of fluid in tissues)

Question 4

Epidemiology of lymphatic filariasis

Answer 4

Human lymphatic filariasis is caused mainly by Wuchereria bancrofti, but also brugia malayi and brugia timori

Estimated 90-120 million people infected in 72 countries, >90% have bancroftian and <10% have brugian filariasis

Vectors
- Culex in urban and semi-urban areas
- Anopheles in rural areas of Africa and elsewhere
- Aedes in islands of pacific

Clinical disease
- 25 million men have genital disease, most commonly hydrocoele
- 15 million mostly women have lymphoedema or elephantiasis of the leg
- LF accounts for 2.8 million DALYs

South american continent, mainly brazil
Guyanas as well
Equatorial africa
Southeast asia

Question 5

Clinical presentation of filiariasis

Answer 5

Adults live in lymphatics
- Dysfunction of lymphatics
- Filarial fever when adults die in lymphatics
- Recurrent
- Fever
- Acute lymphangitis

Acute dermatolyphangioadenitis – inflammation of lymph node, lymphatics and overlying skin

Lymphoedema

Chronic damage to lymphatic leads to progressive lymphoedema

men get scrotal hydrocele, fluid accumulates in membrane surrounding scotum

tropical pulmonary eosinophilia

Question 6

What is acute filarial lymphangitis (filarial fever)?

Answer 6

Adult worms have died in lymphatics causing acute inflammatory response.

cumulative damage to lymphatics causes accumulation of fluid (particularly in lower limbs) causes lymphoedema.

acute dermatolymphangioadenitis related to secondary bacterial infection that defers damage to lymphatics.

Question 7

How does hydrocele occur?

Answer 7

Results from accumulation of fluid

Get damage to lymphatics around it that drain scrotum

Accumulation of fluid around scrotum, scrotum enlarges, over time get elephantiasis

Elephantiasis of breast, key to prevent further progression of elephantiasis and secondary infections is cleaning the swollen legs twice a day with soap and water

Major impact in rural communities for agriculture productivity

Question 8

Tropical pulmonary eosinophilia

Answer 8

W.bancrofti microfilariae (mf) sequestered in lungs during the day
During day microfilariae stay in lungs, at night they go into blood

In the lungs they can cause an allergic type response.

Hypersensitivity reaction to mf in pulmonary blood vessels <1% of patients
- Absent mf on blood films because you have strong immune response to mf
- So you have to do blood sampling at night because that’s when you find mf in blood, but you may not find them because there are v few mf with a strong immune response

Typically men in 20-40s
Presents as chronic, non-productive cough which is more severe at night, wheezing, fever
Weight loss, malaise, adenopathy

On chest x-ray you see diffuse nodular infiltrate

Eosinophilia, elevated IgE and anti-filarial antibodies

Untreated may progress to interstitial fibrosis of lungs

Question 9

Social impact of the disease

Answer 9

Sexual disability

Communities frequently shun those disfigured

Inability to work

Women with visible signs may never marry or spouses and families will reject them

Question 10

Diagnosis

Answer 10

Thick smears using capillary blood at night for W.bancrofti 10pm to 2am

Knotts technique using 1mL blood

Rapid tests to detect circulating antigen

Anti-filarial IgG antibodies

PCR to detect parasite DNA in blood

Ultrasound – filarial dance sign

Question 11

Management of filariasis

Answer 11

Treating the infection: DEC (6mg/kg per day) for 12 days in bancroftian filariasis and for 6 days in brugian filariasis, repeated at 1-6 monthly intervals if necessary

Ivermectin

Albendazole

Side effects: headaches, fever, myalgia, lymphadenopathy and occasionally rash, itching

Question 12

Managing LF, lymphoedema and hydrocele

Answer 12

Acute dermatolymphangioadenitis managed with antibiotics, antipyretics, analgesics

Lymphoedema and elephantiasis managed with hygiene, antibacterial creams, antifungal creams

Hydrocoele managed with surgery

Question 13

treatment and management of elephantiasis

Answer 13

Prevention
- Mosquito nets, insect repellents

Voodoo healing techniques
Elevate and exercise affected body part

Skin treatment
- Wash area twice daily
- Antibacterial cream

CDP (complex decongestive physiotherapy)
- Lymph drainage, massage, compressive bandages

Question 14

What is the current reigmen to eliminate LF transmission?

Answer 14

Once yearly single dose two or three drug regimen as community-based MDA

Ivermectin + DEC + albendazole

Where onchocerciasis is co-endemic, ivermectin+albendazole

Where loiasis is co-endemic, albendazole alone

Question 15

What is onchoceriasis/ river blindness?
Geographic distribution?

Answer 15

Major blinding disease
Caused by filarial parasite Onchocerca volvulus
Transmitted by blackflies

Formerly in parts of latin america, in most of these areas it is now eliminated
Still endemic in venezuela and brazil and countries in africa

Question 16

Transmission of onchoceriasis?

Answer 16

Infection transmitted by simulium black flies, transmit microfilaria

Microfilaria will develop either into males or females

Females live under skin in fibrous nodules, males migrate from nodule to nodule, fertilising females.

Females release thousands of microfilaria which are found in the skin

In a blood meal the blackfly will take up microfilaria to keep up the life cycle.

Question 17

Pathology of onchoceriasis?

Answer 17

Repeated episodes of inflammation to presence of microfilariae leads to permanent damage and scarring in skin and eyes

Adults within subcutaneous nodules do not cause pathology except where they interfere with movement e.g at joints

Question 18

Cllinical disease onchoceriasis

Answer 18

Onchocercal nodules under skin
Skin disease
- Acute papular onchodermatitis
- Chronic onchodermatitis
- Sowda

Eye disease
Anterior segment
- Punctuate keratitis
- Acute iridocyclitis
- Sclerosing keratitis

Posterior segment
- Optic neuritis/atrophy
- Chorioretinopathy

Question 19

Subcutaneous nodules, acute papular onchodermatitis, sowda, chronic onchodermatitis, hanging groin in onchocerciasis

Answer 19

On the head, females release microfilaria which can invade the eyes
If you cut open nodules you see females

Acute papular onchodermatitis
- Allergic inflammatory response caused by microfilaria in skin
- Papules represent where microfilaria has been recognised by immune response

Sowda
- Extreme hypersensitivity to presence of microfilaria
- Blackening of skin
- Localised sowda

Chronic onchodermatitis
- Chronic damage to skin and elastin collagen in the skin causes premature aging of skin
- Particularly around thighs and buttocks where most nodules are found
- Hyperkeratosis to skin due to secondary infections

Hanging groin - Loss of elasticity to skin, causes large inguinal lymph nodes hanging over groin

Question 20

What are eyes examined for in onchoceriasis?

Answer 20

Front of eye you get punctuate keratitis, where microfilaria invade corneal stroma and you get inflammatory response around it - resolves without scarring

Inflammation of iris, iris sticks to lens – iritis

Blockage of fluid from anterior chamber resulting in glaucoma

With repeated episodes of inflammation you get vascularisation of cornea, sclerosing keratitis – causes blindness

Question 21

What is chorioretinopathy and optic atrophy

Answer 21

Back of eye, normally optic nerve is seen

With onchocerciasis you see mothling lateral to pigment epithelium

Pigment epithelium and retina overlying dies, overtime becomes extensive, get pigment clumping and you see sclera underneath

Damage to nerve cells and secondary damage to optic disc

Optic atrophy from microfilaria alone, causing inflammation resulting in damage to optic disc

Question 22

How do you diagnose onchoceriasis?

Answer 22

Using a punch of skin from around the hips, put it on slide with saline and look under microscope

Can see microfilaria

Also take nodules and cut them open to see adult worms inside

Antibody test to pick up exposure to infection

Question 23

Treatment of onchoceriasis

Answer 23

Macrofilaricidal drugs – kill adults
- Suramin – anti cancer drug, severe side effects
- Amocarzine – severe side effects
- Tetracycline – daily for 6 weeks but effective

Microfilaricidal drugs – more widely used - - Diethylcarbamazine – adverse effects e.g papular dermatitis
- Ivermectin – less effects

Question 24

Control strategies for onchoceriasis

Answer 24

Nodulectomy
- Systemic campaigns of nodulectomy reduced microfilarial burdens in Ecuador and Mexico

Vector control
- Extremely effective in volta River basin but suspended in 90s because complex to administer and expensive

Ivermectin
- Introduced in early 90s
- Now mainstay of control
- Treatment annual or semi-annual

Others
- Tetracycline, moxidectin, flubendazole

Question 25

What is loaisis?

Answer 25

Eye worm infection transmitted by chrysops fly which causes a painful bite

Transmit L3 larvae, which develop into adults, migrate through tissues under the skin

Female produces thousands of larvae found in peripheral blood

Chrysops fly takes up microfilaria from blood and continue life cycle

Question 26

Epidemiology of loaisis

Answer 26

Loa loa found in west and central africa

Transmitted by bites of deerflies (genus Chrysops), most common during rainy season and found in high-canopied forest

Human and baboon natural hosts

People most at risk for loiasis are those who live in certain rain forests in west and central africa

Estimated 3-13 millions infected

Adult females 5-7cm, males 3cm long

Question 27

Clinical presentation of loasis

Answer 27

Asymptomatic
- Adult worms migrate through subcutaneous tissues at 1cm/min and can survive up to 17 years
- However increased mortality in heavily infected

Eye worm
- Takes a few hours to a weak to cross sclera
- Accompanied by conjunctivitis and swelling
- Sometimes worm can get lost

Recurrent calabar swellings
- In tissues where worms die it causes inflammatory reactions, calabar swellings
- Extremities and face, generally painless
- Painful near joints

Rare
- Invasion of brain by microfilaria causing meningoencephalitis
- Renal-immune complex mediated or mechanical trauma from mf
- Endomyocardial fibrosis

Calabar swellings
- Episodic angioedema
- Most commonly affects extremities
- Lasts 1-4 days

Question 28

Diagnosis of loasis

Answer 28

Definitive diagnosis
- Detection of microfilaria in daytime blood
- Identification of adult worm in the subconjunctiva or subcutaneous tissue
- PCR using loaf loa repeat sequence

Presumptive diagnosis
- Compatible clinical picture and positive antifilarial antibodies
- Problematic due to geographical, serologic and clinical overlap with other filarial infections

Question 29

Treatment of loasis

Answer 29

DEC (diethylcarbamazine) treatment of choice for those with no or few circulating mf
- DEC 8-10 mg/kg/day for 21 days
- May be severe side effects among those with high levels circulating microfilariae

Albendazole useful in DEC- refractory cases or to reduce mf counts

Ivermectin
- May be severe, life-threatening side effects among those with high levels circulating microfilariae (ie >3000 mf/ml)

Prophylaxis
- Weekly DEC in travellers to endemic areas
- Avoid chrysops bites

Question 30

Control of loasis

Answer 30

No control programmes but many areas are co-endemic with onchocerciasis and/or LF where control programmes are in operation
- Co-endemic regions with onchocerciasis prelude use of ivermectin in MDA for loa loa
- Recommendation for twice annual albendazole in co-endemic regions but epidemiology inadequate