Nematoda 3 III

What does Onchocerca volvulus cause? What is the only host?

It causes onchocerciasis or river blindness. Humans

Where is onchocerciasis prevalent throughout?

Eastern, central, and Western Africa where it is the major cause of blindness. It is also found in Guatemala, Mexico, Colombia, and Venezuela in the Americas

Where is Onchocerciasis confined to?

Neighbourhoods of low elevation with rapidly flowing small streams where black flies breed

What is Onchocerciasis caused by?

By a filaria worm 

How does the worm get into a human?

Through the bite of a blackfly

Where do black flies live?

They live by fast-flowing streams and rivers, thus those who are infected usually live close to such bodies of water, giving it the nickname river blindness

What happens once the worm is in the skin?

It births thousands of microfilariae which move to the eyes and the skin

What happens when microfilariae die?

Their decomposing bodies produce toxins that cause extreme itchiness and lesions. After enough time, this toxicity causes blindness and extreme skin disfiguration 

What is a genera of black fly that will transmit river blindness? How do black flies feed?

Simulium sp. They will chew holes in the skin and then through a tiny proboscis they will suck the blood.

Describe the life cycle for Onchocerca volvulus

1. Black fly (genus simulium) takes a blood meal and L3 larvae enter bite wound (I)

2. The L3 larvae will now be in subcutaneous tissues

3. Adults will be in subcutaneous nodule after 8-10 months

4. Adults produce unsheathed microfilariae that typically are found in skin and in lymphatics of connective tissues, but also occasionally in peripheral blood, urine, and sputum (D)

5. Black fly will take a blood meal and ingest microfilariae

6. Microfilariae penetrate blackflys midgut and migrate to thoracic muscles

7. L1 larvae

8. L3 larvae

9. Migrate to head and blackflys proboscis and the whole cycle repeats

What do the adults typically occur as for Onchocerca volvulus?

Usually occur as a group of tightly coiled worms (2-3 females and 1-2 males)

What are microfilaria?

They are a pre-larvae or advanced embryos which will develop into the first stage larvae (L1) in the arthropod vector. In simple terms it is the stage which develops from the egg

In most tissue-dwelling species, where are the eggs hatched and released? What about for blood-dwelling species?

The eggs hatch in the uterus of the female and the unsheathed microfilariae are released. For blood-dwelling species, embryonated eggs are released and they will only hatch after being ingested by the arthropod intermediate host

What do all microfilariae burrow through and develop into? Are many of the organs of microfilariae in a very early or late stage of development?

Burrow through the stomach wall after being eaten by the arthropod host and develop into infective third stage larvae (L3). Early stage

What do the microfilariae of many species undergo?

A development phase called the sausage stage, which is where they become temporarily shorter and thicker while the first stage (L1) larval organs develop 

What can be said about the release of microfilariae in some species of Onchocercidae?

The release by the adult female is periodic, occurring daily at a particular time of the day or night

What does the timing of the release of microfilariae increase the chance of?

Increases the chance that they might be picked up by a blood-feeding arthropod vector which are often more active at certain times of the day.

What does onchocerciasis result in?

1. Nodular and erythematous lesions in the skin and subcutaneous tissue due to a chronic inflammatory response to persistent worm infection

2. Eosinophilia and urticaria during the incubation period of 10-12 months 

3. Photophobia, lacrimation and blindness 

What is urticaria? What is lacrimation?

It is a kind of skin rash notable for dark red, raised, itchy bumps. Lacrimation is tear production  

Why might someone develop photophobia, lacrimation, and blindness from Onchocerciasis?

This is because ocular involvement consists of trapping of microfilaria in the cornea, choroid, iris and anterior chambers

What is diagnosis of Onchocerciasis based on?

Based on symptoms, history of exposure to black flies and presence of microfilaria in nodules 

What medication is effective in killing the worm? What might someone be given corticosteroids when they are treating onchocerciasis?

Diethylcarbamazine. This is because destruction of microfilaria produces extreme allergic reactions which can be controlled by corticosteroids

What preventative measures are in place for onchocerciasis? Can the worms be removed? Why are so many people still getting infected?

Vector control and treatment of infected individuals and avoidance of black fly. No. This is because it is difficult to transport medication here

What is the common name for loa loa? What does it cause? Where is it limited to?

Eye worm. It causes loasis. It is limited to the areas of African equatorial rain forest 

What is loa loa an agent of? What is it transmitted by? Can it be removed from eyes?

It is an agent of filariasis. It is transmitted by deer flies. Yes it can be

Is the life cycle the same as onchocerca?

Yes it is, the only difference is that the deer fly is the one taking a blood meal and ingesting microfilariae.

What genera of deer flies is transmitting loa loa?

Chrysops sp.

What does loasis result in? What is the rate that loa loa migrates under the skin at?

Subcutaneous swelling (called Calabar). At a rate of up to an inch every two minutes 

What is calabar swelling marked by? Does the swelling appear spontaneously? How long does it persist for?

It is marked by erythema and angioedema usually in the extremities. Yes it does and persists for 4-7 days before it disappears.

Does loa loa cause any serious problems?

No it doesn’t except when passing through the orbital conjuctiva or the nose bridge

What is diagnosis of loa loa based on?

Based on symptoms, history of deer fly bite and presence of eosinophilia. Recovery of worms from the conjuctiva is confirmatory though

What is the treatment and control for loa loa?

It is the same as onchocerciasis 

What is the common name for dirofilaria immitis? What is it? Where does it occur in?

Canine or dog heart worm. It is a common parasite of dogs in many parts of the world (mainly US). It occurs in many other animals such as cats but it rarely infects humans

Where does dirofilaria immitis live?

Live in the dogs pulmonary artery and right heart

Do males or females produce microfilariae for dirofilaria? What is the primary method of diagnosis?

Female worms and demonstration of microfilariae in blood is the primary method of diagnosis.

When are microfilariae of dirofilaria immitis ingested? What happens after this?

They are ingested by a mosquito when it feeds and the microfilarie mature into infective juveniles in the vector and the infection is transmitted to a new host when the mosquito feeds.

What is the vector for dirofilaria immitis?

Many species of mosquitos

What are symptoms of canine heart worm? Why do these symptoms occur? Can the disease be fatal?

Respiratory insufficiency, chronic cough, and vomiting because of inflammation and thickening of the heart. Yes it can be

How can canine heart worm be treated?

Through immiticide if the worm is still small. Also a number of effective chemoprophylactic agents are available for this species.