Toxocara

Question 0

Toxocara eggs are present in the faeces of infected dogs. Another dog may ingest these eggs in their food or by licking their coat. The eggs hatch into larvae in the dog’s intestine from where they migrate into…

Answer 0

Various organs in the dog

Question 1

Toxocara canis is a roundworm that lives in the…

Answer 1

Gut of dogs, but it can sometimes infect humans

Question 2

The eggs don’t develop any further in adult dogs, however when a female dog becomes pregnant, these larvae become…

Answer 2

Reactivated and migrate back to the intestines where they develop into adult worms. Larvae also migrate to the placenta where they can infect the foetal puppies and the mammary glands where they can infect the young puppies in milk

Question 3

Life cycle of Toxocara canis:

Answer 3

1) Dog (larvae become active when female dog is pregnant)
2) Larvae from mother infect puppies via placenta or milk
3) Puppy (larvae become adults in the puppy’s intestine)
4) Adults produce eggs that are released in the puppy’s faeces
5) Eggs in the soil accidentally swallowed by humans and animals
6) Humans

Question 4

Larvae in the puppy’s intestines migrate from the intestine via the blood system to the lungs, then they migrate through the bronchi, bronchioles and trachea to the oesophagus where they are…

Answer 4

Swallowed and return to the intestine and develop into adult worms

Question 5

Toxocara enter humans when the eggs are…

Answer 5

Swallowed and hatch into larvae that cause illness but cannot reproduce

Question 6

Children are most vulnerable, they can become infected when they…

Answer 6

Ingest soil contaminated with eggs or even ingest soil invertebrates

Question 7

Humans are also susceptible to Toxocara by stroking a dog that has …

Answer 7

Eggs in the hair or by letting an infected dog lick their face

Question 8

Infection occurs in humans when a…

Answer 8

Fertile egg is eaten

Question 9

Second stage of infection is larvae hatch in small intestine and…

Answer 9

Burrow into the lining of the intestine

Question 10

Third stage is the larvae enter the blood vessels and travel to the…

Answer 10

Liver - some larvae are trapped in the liver

Question 11

Fourth stage, larvae enter the systemic circulation and may travel to any organ…

Answer 11

These larvae do not develop further

Question 12

Fifth stage, occasionally the larvae migrate to organs, such as the eye, where they can cause:

Answer 12

Pain and problems with vision such as damage to retina (blindness)

Question 13

Other organs that may be infected are:

Answer 13

Lungs, heart, kidneys, brain and liver

Question 14

Toxocara eggs in faeces can also be passed onto other…

Answer 14

Species

Question 15

When in another species the eggs hatch into larvae in the intestines and then…

Answer 15

Migrate to the tissues, do not develop further

Question 16

If a dog or cat kills or eats an infected animal the larvae become active in the intestines and…

Answer 16

Infects the dog or cat that has eaten them

Question 17

In humans infected organs can be damaged, and in rare cases infection =

Answer 17

Fatal

Question 18

The adaptations of Toxocara are:

Answer 18

• Mature eggs = very sticky, can attach to animals’ fur birds beaks (increases chances that they will infect new host)
• Worm has hooks (hold in place in intestine)
• Worm doesn’t have highly developed locomotory structures (stays in hosts intestine)
• Worm has poorly developed nervous system
• Worm has a thick, resistant cuticle (resistant to hosts enzymes)
• Highly developed reproductive organs (worm can produce enormous numbers of fertilise eggs)
• Worm can respire in low oxygen conditions in the intestine
• Worm can produce antienzymes (reduce the damage might be caused by the host’s enzymes)
• Larvae form cysts of fibrous tissue around them when in the host’s tissues (immune system are less able to reach them, also means that the parasites antigens are less likely to be detected)
• Larva sheds its cuticle regularly & replaces it (antibodies and white blood cells that attach to the worm are also shed, reducing damage that is down to the larva)