Nematodes and zoonotic nematodes Flashcards
Why would humans get infected with zoonotic nematodes?
Often we are accidental hosts.
Some can develop fully in humans whereas some arrest development.
How many trichonella species infect humans?
7 spp. E.g. trichonella spiralis
What is the distribution of trichonella spiralis and why is it a problem? What is it a disease of?
From the arctic to the tropics, is Mr Worldwide.
Is a major economic problem in porcine animal production.
Is a disease of meat eaters! Infects carnivorous and omnivorous animal tissue.
Describe the infection cycle of trichonella spiralis.
Is ingested –> emerges in the duodenum –> burrows into the intestinal mucosa where they mate –> the females then give birth to L1 larvae –> L1 penetrate through intestinal wall –> enter into blood and lymphatic circulation -> invade muscle cells and transform into a nurse cell (produce a nest inside of which is a coiled intracellular L1 with surrounding collagen).
Describe the infection cycle of trichonella spiralis.
Is ingested –> emerges in the duodenum –> burrows into the intestinal mucosa –>
What is the domestic cycle for t spiralis? What is the main source of human infection?
domestic cycle in rats and pigs. Pigs are the main source of human infection (eating pork).
What is the domestic cycle for t spiralis? What is the main source of human infection?
domestic cycle in rats and pigs. Pigs are the main source of human infection.
How long do larvae remain infective for within decaying meat?
Months!
What is something interesting to note about the temporal epidemiology of t spiralis cases?
Often cases are clustered and are associated with a particular feast or festival where large numbers of people would be eating infected pork.
How can horses also be a source of infection for t spiralis?
If infected rats get ground up in horse fodder and fed to the horses.
What is the arctic cycle of t spiralis and who does this present a problem for?
Arctic cycle in polar bears, arctic foxes and walruses. This is a problem for Inuits who eat raw meat which may be contaminated.
(There was a 50% prevalence in Alaskan Inuits in the 80s).
What animals are involved in the African cycle of t spiralis?
Bush pigs, warthogs and lions etc.
What determines the severity of infection with t spiralis?
The number of infective larvae strongly correlates with the infection severity, and produces a spectrum of pathology.
What is the host response as T spiralis larvae migrate out to muscle tissue?
An acute inflammatory response is produced. Swelling of the tongue and eyelids is often seen.
What are the symptoms often associated with a heavy infection of T spiralis?
Myocarditis, pneumonitis, diarrhoea.
If the larvae migrate through the CNS, neurotrichonellosis can occur as well as sublingual bleeding, rashes and fatality.
What is the chronic stage of T spiralis?
The cyst formation stage in tissues.
How would we diagnose T spiralis?
Look at the dietary history (e.g. could be linked with community epidemics), use serology or a biopsy.
How do we treat t spiralis? When should treatment be administered?
Early treatment is essential as it is hard to treat once encystment in muscles occurs. Treat with antihelminthics within the first few weeks, if not use long term corticosteroids for control if this window is missed.
-Albendazole or mebendazole
How do we control trichonella spiralis?
- Cook food above 55 degrees or freeze below -fifteen degrees for 20 days (species dependent).
- Meat inspection in abattoirs
- Don’t feed pork to pigs.
Where are the majority of cases of capillaria phillipinensis?
China, Phillipines, Thailand.
What is the main definitive host for capillaria philipinensis?
Marine birds.
What is the transmission cycle between the definitive host and humans for C philipinensis?
Eggs from marine birds are eaten by fish and human acquire infection by eating raw or undercooked fish.
Describe the pathogenesis produced by C phillipinensis.
Adults reside in the mucosa and produce a severe inflammatory response.
This parasite can cause internal autoinfection which can lead to a huge parasitic burden.
Malabsorption and protein loss are part of the pathogenesis.
How do we diagnose c philipinensis?
Look in the stool for eggs. They look similar to trichirus but are smaller and not as lemon shaped.
How do we treat c philipinensis?
Prolonged benznidazole treatment. Only the adults are susceptible and the juveniles are not affected which means the longer treatment takes into account the maturation of the juveniles.
What are the two types of pathology that toxocara species can produce?
Visceral larval migrans and ocular larval migrans.
What are the two main species of toxocara?
Canis and cati (from dogs and cats respectively).
Which age group is affected most by Toxocara?
Peaks in children.
What is the lifecycle of toxocara?
Adults are in the intestines of puppies and cats and eggs are excreted in the faeces –> the larvae arrest at L2 if in the adult dog but puppies can become infected if the female is pregnant –> humans can swallow eggs where they develop into L2 larvae which then migrate –> migration and death of the larvae causes an inflammatory response.
What ist he most common serial pathology found with toxocara.
Occular larval migrans. Granuloma forms in the retina where the larvae are trapped.
How do we diagnose toxocara?
Not egg detection as eggs are not shed so we cannot see them.
WE look at exposure history (exposure to young dogs or contaminated soil) and look at typical clinical signs as well as doing blood tests.
How do we treat toxocara?
Albendazole and corticosteroids.
What is the paediatric presentation of toxocara?
Unexplained febrile illness, eosinophilia.
How do we control Toxocara?
- Wash dogs (remove eggs from fur)
- Hand washing after play
- Deworm puppies
- Raw chicken liver consumption avoidance
What is the latin name for the rat lungworm?
Angiostrongylus catonensis
What does angiostrongylus catonensis cause in humans?
Eosinophilic meningitis.
What is the geographical epidemiology of angiostrongylus catonensis?
South Asia and Pacific region, also Africa and the Caribbean.
What is the lifecycle of angiostrongylus cantonensis?
The life cycle is complex and involves a rodent definitive host and an appropriate mollusk intermediate host, usually land snails or slugs (Fig. 6). Adult worms mature in rat brains, enter the central circulation, and mate in the pulmonary arteries producing eggs. The eggs become first-stage larvae that penetrate pulmonary vessels to access the respiratory tree, where they are coughed up, swallowed, and excreted in feces. These second-stage larvae must be consumed by land snails or slugs in order to mature into infective third-stage larvae, be eaten by rodents, and maintain the parasite’s life cycle. Man becomes a dead-end host by consuming raw intermediate mollusk hosts, or food items contaminated by their slime, or by consuming raw, crustacean (shrimp, crabs, fish, frogs) transport, or paratenic, hosts that consumed infected mollusks. In man and paratenic hosts, the neurotropic larvae migrate to the central nervous system (CNS) (neural larva migrans) seeking to mature into young adults as in rat brains, but eventually die causing EM.
How is angiostrongylus cantonensis acquired?
By eating slugs/snails, contaminated salad, anything contaminated with snug/snail slime.
Is angiostrongylus cantonensis fatal?
Can be benign OR fatal depending on if a strong granuloma is produced which may cause focal necrosis in the brain or anterior chamber of the eye.
How is angiostrongylus cantonensis diagnised and treated?
Antihelminthics are NOT given as this could produce an even stronger inflammation which could be fatal if it causes focal necrosis in the brain or eye.
Where is anisakid acquired from?
Raw fish
What are the two types of anisakid? What do they infect?
Simplex and dicipiens. Infect marine mammals. They live in the gut and viscera of fish (not gutting directly after catching can cause the parasites to spread into the tissue of the fish.
What is the lifecycle of anisakis?
Adult stages of anisakid nematodes 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 image . The eggs become embryonated in water, undergoing two developmental molts, and hatch from the eggs as free-swimming ensheathed third-stage (L3) larvae. These free-swimming larvae are then ingested by crustaceans. The ingested larvae grow within the crustacean hemocoel, and become infective to fish and cephalopod paratenic hosts. After preying upon infected crustaceans, the digested L3 larvae migrate from the paratenic host intestine into the abdominal cavity, and eventually to the tissues of the mesenteries and skeletal muscle. Through predation, tissue-stage L3 larvae can be transmitted among paratenic hosts. Fish and squid maintain L3 larvae that are infective to humans and marine mammals.
When fish or squid containing third-stage larvae are ingested by definitive host marine mammals, the larvae molt twice and develop into adult worms. After ingestion by humans, the anisakid larvae penetrate the gastric and intestinal mucosa, causing the symptoms of anisakiasis.
What is the pathogenesis seen in anisakis infection?
Epigastric/ abdominal pain, vomiting.
Infection is self-limiting as larvae die and the infection resolves.
However, as it is so immunogenic, secondary exposure can provoke extreme anaphylaxis in previously sensitised people.
How do we diagnose anisakis?
Ask about previous exposure to raw fish.
Often mistaken for peptic ulcers and appendicitis.
How do we control for anisakis?
Freeze fish at -20 for 24 hours. Cook fish.
How do we treat anisakis?
Hard, some reports of effective treatment with albendazole.
Describe the geographical epidemiology of gnathostoma spinigerum.
SE Asia and Central and South America.
What is the lifecycle of gnathostoma spinigerum?
In definitive hosts (cats, dogs and pigs), adult worms of most Gnathostoma spp reside in a tumor-like mass in the gastric wall; adult worms of some species are found in the esophagus or kidney. Adults mate and produce unembryonated eggs, which pass through a small opening in the tumor-like mass and ultimately into the feces. Eggs become embryonated in water, and eggs release sheathed first-stage larvae (L1). Freshwater copepods, which serve as first intermediate hosts, ingest the free-swimming L1, and the larvae molt twice to become early third-stage larvae (EL3). Following ingestion of the copepod by a suitable second intermediate host, the EL3 migrate into the tissues of the host and develop further into advanced L3 larvae (AL3). When the second intermediate host is ingested by a definitive host, the AL3 develop into adult parasites in the gastric wall. Alternatively, the second intermediate host may be ingested by a paratenic host, in which the AL3 do not develop further but remain infective. Humans become infected by eating raw or undercooked meat of second intermediate or paratenic hosts containing AL3. In the human host, AL3 migrate in various tissues and may develop into immature adults but never achieve reproductive maturity; they may range in size from 2 mm to about 2 cm depending on the species and the extent of development. Whether humans can become infected by drinking water that contains infected copepods is not clear
How long do the larvae of gnathostoma spinigerum live?
Long lived! About 10 years.
What are the clinical symptoms of gnathostoma spinigerum?
The clinical symptoms depend on the migration of the larvae, whether it is visceral or subcutaneous.
We see migratory oedema (Migration in the subcutaneous tissues (under the skin) causes intermittent, migratory, painful, pruritic swellings (cutaneous larva migrans). Patches of oedema appear after the above symptoms clear).
OR can cause eosinophilic meningitis.
How do we diagnose gnathostoma spinigerum?
Use serology, clinical history (e.g. eosinophilia, migratory lumps, diet).
How do we treat gnathostoma spinigerum.
Prolonged benznidazole and ivermectin (also perhaps albendazole)- it may never be cured!
How do we control for gnathostoma spinigerum?
Cook freshwater fish (about 5 minutes at 75 degrees).
What are the two phyla of helminths and what are the two classes within one of these phyla?
Platyhelminths and nematodes (phyla) and cestodes and trematodes (class).
Trematodes being flukes and cestodes being tapeworms.
