Lecture 8

Question 1

Which filarial parasites cause lymphatic filariasis?

Answer 1

Wuchereria bancrofti
Brugia malayi
Brugia timori

Question 2

What causes onchocerciasis?

Answer 2

Onchocerca volvulus

Question 3

What causes tropical eye worm?

Answer 3

Loa loa

Question 4

What are the vectors for each filarial parasites?

Answer 4

• Wuchereria bancrofti, brugia malayi and brugia timori : mosquitos
• Onchocerca volvulus : black flies
• Loa loa : Tabanid flies

Question 5

Why is distirbution of Wuchereria bancrofti wider than of Brugia?

Answer 5

More mosquito species can transmit Wuschereria

Question 6

When does a Loa loa infection become dangerous?

Answer 6

During a coinfection with Onchocerca

Question 7

Outline the life cycle of the lymphatic filarial worms

Answer 7

L3 (infectious larvae) burst out mouth of mosquito (too large for proboscis) and enter skin through mosquito bite site. Travel to the lymphatics and moult to form L4 and then adult, over around 3 months. Adults produce 100’s of microfilariae (L1 larvae), 100-200µm in length, per day. Microfilariae travel to blood where can they be picked up by mosquito during blood meal. L1 larvae travel to flight muscles and undergo moult to L2. L2 moults to L3 and travels to mouth. L1 to L3 in mosquito takes 14 days; exact time between feeding of female mosquito.

Question 8

What is meant by microfilarial periodicity?

Answer 8

They make themselves available in the peripheral blood during the time of day that the vector feeds. 3 types; nocturnal periodic, diurnal periodic and nocturnal sub-periodic Also helpful in avoiding the spleen.

Question 9

Outline the life cycle of Onchocerca volvulus

Answer 9

Black fly takes a blood meal and transmit L3 into blood wound. Initially enter lymphatics but travel to subcutaneous tissues, in particular bony protrusion, and develop into adults. Females form nodules, in which they are surrounded by fibrotic tissue, which males travels between to fertilise. Microfilariae are released and travel to skin, lymphatics, blood, urine and sputum. Black fly takes blood meal and infected by microfilariae in skin. Microfilariae penetrate midgut and travel to thoraic muscles to develop into L3 and then to mouth for next infection.

Question 10

What makes up the nodules?

Answer 10

Balls of females but also host inflammatory cells, collagen and ECM

Question 11

Outline the life cycle of Loa loa

Answer 11

Tabanid flies take blood meal and transmit L3 into blood wound. Initially enter lymphatics but travel to subcutaneous tissues and develop into adults. Males and females are migratory and move. Sheathed microfilariae are released and travel to spinal flouid, urine, sputum, peripheral blood and lungs. Tabanid flies takes blood meal and infected by microfilariae. Microfilariae shed sheath and penetrate midgut. Travel to thoraic muscles to develop into L3 and then to mouth for next infection.

Question 12

What diseases are caused by lymphatic filariasis?

How?

Answer 12

• Filarial lymphoedemas; elaphantiasis and hydrocoele

Due to adults dying in the lymphatics causing irreparable damage to the lymphatics and loss of ability to remove fluid

Question 13

What diseases are caused by onchocerciasis?

How?

Answer 13

• River blindness
• Dermiitis

Due to microfilariae dying

Question 14

What effect can treatment for onchocerciasis have when patients have Loa loa coinfection?

Answer 14

Death of Loa loa microfilariae in nervous system can cause coma and death

Question 15

Which endobacterium is seen in the species, except Loa loa, studied in this module?

Answer 15

Wolbachia

Question 16

Where do you find Wolbachia in the worms?

How is it transmitted

Answer 16

In the hypodermis

Transmitted by the females into the microfilariae; bacteria found in the embryonic stem cells of their ovaries

Question 17

What happens to the Wolbachia in embryogenesis?

Answer 17

Asymmetric mitotic segregation of Wolbachia into only the hypodermal cells

Question 18

What happens to the numbers of Wolbachia in the host?

Answer 18

Stays low in insect vector then increases during development in human host (temperature)

Question 19

What processes does Wolbachia affect?

Answer 19

• Larval development
• Embryogenesis
• Longevity of adults

Question 20

Which genes does Wolbachia have?

Answer 20

Undergoing reductive evolution (on way to organelle)

Remaining genes for heme biosynthetic pathway, vitamin co-factors and excess nucelotide provision

Question 21

Why are the Wolbachia genes needed?

Answer 21

Provide components needed by the worms, especially during rapid growth

Question 22

Which Wolbachia function has been shown to be essential?

Answer 22

Heme biosynthesis; worms can’t make themselves and die without it

Question 23

What genetic interactions have occurred between Wolbachia and the nematodes?

Answer 23

Lateral gene transfer; Wolbachia genes found in species that are now Wolbachia negative

Question 24

How has Wolbachia been shown to be the major driver of innate inflammation?

Answer 24

• Nematodes without Wolbachia symbiote, Loa loa, have no innate inflammation seen in the Wolbachia positive nematodes in vitro
• Removal of Wolbachia, by tetracycline treatment, from nematodes causes loss of inflammatory response in vitro
• In vivo treatmnet with doxycycline shows nodules with fewer nuetrophils

Question 25

How does Wolbachia interact with the innate immune system?

Answer 25

Toll-like receptors (TLR) 2 and 6, with adaptor protein MyD88, recognise peptidoglycan associated lipoprotein (PAL) and Type IV secretory pathway VirB6 components (VirB6) on Wolbachia

Question 26

How does Wolbachia lead to river blindness during a Onchocerca volvulus infection?

Answer 26

Death of microfilariae releases wolbachia into eye, recognised by TLR2/6 and neutrophils are recruited, release their granules and cause visual impairment

Question 27

Why does treatment with anti-filarial’s of Wolbachia positive nematodes sometimes have adverse effects?

Answer 27

Death of the nematodes causes release of the Wolbachia

Question 28

Why do 3/5 patients not develop filarial lymphoedema?

Answer 28

These patients display suppressed T cell responses to helminth antigens. Up regulation of regulatory T cells and immunosuppressive cytokines

Question 29

What is the target for the drugs currently used?

Answer 29

The microfilariae; so stop transmission

Question 30

What treatment strategy is being used for filariasis?

Answer 30

Mass drug administration
- DEC and Albendazole (out of Africe)
- Ivermectin and Albendazole (In Africa)
Both treatments are given once a year for 4-6 years; until the adults are dead. Requires mass use across entire range of parasite

Question 31

What treatment strategy is being used for onchocerciasis?

Answer 31

Give Ivermectin once a year (or more) to suppress microfilariae in skin and stop transmission. Will need >20 years and >80% coverage to fully break the cycle

Question 32

What environment treatment has been used in west Africa to stop onchocerciasis?

Answer 32

Insecticides in water sources to kill the black flies

Question 33

What are the challenges to African Programme for Onchococerciases control?

Answer 33

• No vector control
• Civil strife
• Insufficient health resources
• Political commitment and funding
• Loiasis (Loa loa coinfection) severe adverse events to ivermectin

Question 34

What is the only curative treatment?

Answer 34

Doxycycline to kill the Wolbachia

• Kills the adults
• Reduces severity of limb lymphoedema
• Kills macrofilariae

Question 35

What are the Doxycycline issues?

Answer 35

1) Long term course of treatment

2) Contraindication in children

Question 36

What is the future?

Answer 36

Curative treatments that work faster then doxycycline; Macrolides real candidates