Lecture 3- Ascarids (Roundworms)

What is the primary mode of oral infection for Ancylostoma caninum?

The lactogenic route, with arrested larvae passed from the mother to nursing puppies.

When may nursing puppies begin to pass Ancylostoma caninum eggs in their feces?

As early as 10-12 days after birth.

What are the two main modes of oral transmission for Ancylostoma caninum?

1. Lactogenic route (arrested larvae passed to nursing puppies)

2. Direct ingestion of infective larvae from environmental sources or paratenic hosts.

What are paratenic hosts in the lifecycle of Ancylostoma caninum?

Intermediate hosts that help transmit infective larvae but are not essential for the lifecycle.

How does Ancylostoma caninum infection affect older animals (>12-15 weeks)?

Older animals are less susceptible to lactogenic transmission and may acquire infection through environmental exposure.

What is the general size and morphology of Roundworms or Ascarids?

Where in the host does Roundworms or Ascarids reside?

in the small intestine

What do Roundworms or Ascarids worms generally feed on?

host ingesta

What illnesses are associated with Roundworms or Ascarids infection?

Intestinal blockage and inflammatory responses from the host

Where does Roundworms or Ascarids develop to its infective stage?

In the environment, outside of the host.

What is the common name for Toxocara canis?

canine roundworm

What is the size range of Toxocara canis worms, and how do males and females differ?

Worms are ~7 to 18 cm long; females are larger, and males have a coiled tail.

How is the mouth of Toxocara canis different from other parasitic worms?

It has three lips rather than a large, open buccal capsule.

What is the basic lifecycle of Toxocara canis?

1. Eggs are passed in the feces of the definitive host.

2. Eggs develop to the infective stage in 2-3 weeks.

3. Larvated eggs are ingested by a host.

4. Larvae hatch, enter the hepatic blood supply, and undergo tracheal migration.

5. Adults reside in the small intestine and pass eggs by 4-5 weeks post-infection.

How many eggs can female Toxocara canis worms produce per day?

Up to 200,000 eggs per day.

What is hypobiosis in Toxocara canis?

A state where larvae are arrested in somatic tissues.

How does vertical transmission of Toxocara canis occur?

1. Puppies are infected in utero around the 42nd day of gestation.

2. Lactogenic transmission may occur but is less significant.

How long can mothers with sequestered larvae continue to infect puppies?

Up to 385 days after the initial infection.

Why is the reservoir of Toxocara canis larvae in dogs' tissues significant?

It allows dogs to continually replenish the reservoir of infective larvae.

What is the facultative indirect lifecycle of Toxocara canis?

1. Ingesting infective larvae from a paratenic host.

2. Paratenic hosts (e.g., rodents, prey, or carrion) are infected by ingesting eggs.

3. Larvae hatch and encyst in the somatic tissues of paratenic hosts.

At what age are patent infections with Toxocara canis most typical?

In puppies less than 3 months old.

What happens to Toxocara canis larvae as puppies age?

Migrating larvae have a decreasing tendency to develop into adult worms and instead divert to somatic tissues where they become arrested.

Why is the arrest of Toxocara canis larvae in somatic tissues significant?

Arrested larvae remain available for in utero transmission to future offspring.

What factors influence the variation in Toxocara canis infections?

Breed, sex, previous exposure, and infectious inoculum.

Which regions in the U.S. have the highest proportion of animals infected with Toxocara canis?

The Northwest, Plains, Midwest, and East Central United States. Although cases are found in every state

What is the national prevalence of Toxocara canis?

1.4%

What is one biasing factor in the data on Toxocara canis prevalence?

Positive fecal examination is correlated with the host's age, and data are based on cooperating clinics, which may not represent true distribution.

How does Toxocara canis pathogenesis differ between young and adult animals?

Young animals are more prone to hyperinfection due to immune naivety.

What are the respiratory consequences of Toxocara canis larvae migration?

Mechanical damage from migration through the alveoli can lead to pneumonia.

What gastrointestinal symptoms are associated with Toxocara canis infection?

Malaise (ADR), vomiting, anorexia, and diarrhea due to irritation in the gut as worms mature.

How does Toxocara canis infection cause hypoproteinemia?

Worm motility, pressure on intestinal epithelium, irritation, and inflammation stimulate tissue leakage.

What causes the pot-belly appearance in animals infected with Toxocara canis?

Leaked plasma proteins pooling in abdominal tissues and worms growing faster than the intestinal tract.

What are the severe consequences of Toxocara canis infection in the intestines?

Blockage of the intestinal lumen and potential rupture of the intestine.

What assumption should be made about puppies and Toxocara canis?

Assume all puppies are born with Toxocara canis.

At what ages should puppies be dewormed to treat Toxocara canis?

Puppies should be dewormed at 2, 4, 6, and 8 weeks of age.

What is the recommended deworming drug for puppies weighing less than 5 lbs?

Pyrantel pamoate (Strongid T) at a dose of 5 mg/kg (or 10 mg/kg for puppies < 5 lbs).

What is the goal of treating Toxocara canis larvae in the GI tract?

To prevent sexual maturation, reproduction, environmental contamination, and reinfection of the host.

Why is monthly prophylactic treatment recommended for puppies during their first year?

To manage infection as parasites are more likely to arrest in somatic tissues as the puppy ages.

What is the purpose of a shorter treatment interval than the ERP (egg reappearance period)?

To ensure effective control of infection and prevent environmental contamination.

Which monthly heartworm prevention drugs are effective against Toxocara canis, and when should they be given?

1. Interceptor (Milbemycin): Starting at 2 weeks, effective against hookworms, roundworms, and whipworms.

2. HeartGard Plus (Ivermectin + Pyrantel): Starting at 6 weeks, effective against hookworms and roundworms.

3. Advantage Multi (Imidacloprid + Moxidectin): Starting at 7 weeks, effective against hookworms and roundworms.

How do most monthly heartworm drugs help in managing Toxocara canis?

By preventing the completion of the lifecycle and reducing the risk of reinfection and environmental contamination.

What is the common name for Toxocara cati?

Feline roundworm.

How large are adult Toxocara cati worms?

Males: 3 to 6 cm

Females: 4 to 10 cm

What morphological feature distinguishes adult Toxocara cati worms?

Prominent cervical alae, which are broad, arrow-like projections of the cuticle.

What are the two main life cycle types of Toxocara cati?

Direct lifecycle

Facultative indirect lifecycle

Describe the direct lifecycle of Toxocara cati.

1. Ingestion of larvated eggs.

2. Eggs hatch and larvae migrate in the hepatic blood supply.

3. Larvae undergo tracheal migration and arrive in the alimentary tract.

4. Eggs are passed in the feces 42-49 days post-infection.

How are adult cats typically infected with Toxocara cati in the facultative indirect lifecycle?

By consuming a paratenic host due to predatory behavior.

What happens to Toxocara cati larvae in paratenic hosts?

Larvae are activated upon ingestion and proceed directly to the small intestine, where they develop into patent adults.

Does vertical transmission of Toxocara cati occur in utero?

No, there is no in utero infection.

When can kittens be infected with Toxocara cati via the lactogenic route?

Only when the Queen is acutely infected during late gestation or lactation.

How do adult felines contribute to the environmental contamination of Toxocara cati?

Adult felines pass eggs in their feces, which contaminate the environment and pose a zoonotic threat.

How does the role of adult felines in Toxocara cati infections differ from adult canines?

Adult felines continue to pass eggs and are significant in environmental contamination, whereas adult canines show immunity with age and do not pass eggs.

What is the primary source of Toxocara cati infection for adult felines?

Consuming paratenic hosts is more common than ingesting larvated eggs.

What is the zoonotic risk associated with Toxocara cati eggs?

Eggs in the environment can infect humans and other hosts, posing a significant zoonotic threat.

What is the national prevalence of Toxocara cati based on positive fecal examinations in 2024?

4.8%

In which regions of the U.S. is the highest proportion of Toxocara cati infections found?

The midwest and northeast. Although it is found in every state

What biasing factors affect the distribution data for Toxocara cati infections?

The data reflects pet cats tested and positive for parasitic infection rather than the actual occurrence of infection in cat hosts across states.

What are common clinical signs of Toxocara cati infection in cats?

Coughing, gagging (similar to choking on a hairball), and worms in feces or vomitus.

How are Toxocara cati eggs identified in fecal examinations?

- Round with a pitted shell and a "sticky" albuminous coat.

= Dark, single-cell embryo.

- Size: 60-70 μm (approximately 65 μm diameter).

Are felines at the same risk of Toxocara cati disease as canines?

No, felines are typically at lower risk, with disease occurring primarily in young, immune-naïve animals

What issues can excessive Toxocara cati worm burdens cause in commercial catteries?

Excess morbidity and mortality, leading to production losses.

What is the effective treatment dose of pyrantel pamoate for Toxocara cati?

Twice the dog dose, but it does not have FDA label approval for use in cats.

Which drug is FDA-approved for treating Toxocara cati in cats?

Pyrantel/Praziquantel (Drontal), for felines >1.5 lbs and >4 weeks of age, with an effective dose of 20 mg/kg.

Besides pyrantel and praziquantel, what other drugs are effective against Toxocara cati?

Selamectin and ivermectin.

What hosts are susceptible to Toxascaris leonina?

Dogs and cats (wild, domestic, and feral).

How does the morphology of Toxascaris leonina compare to Toxocara canis and Toxocara cati?

- Similar in size.

- Alae are linear and narrow, like T. canis.

- Different digestive tract morphology.

What are the two life cycle types of Toxascaris leonina?

1. Direct life cycle: Ingestion of larvated eggs.

2. Facultative indirect life cycle: Ingestion of infective larvae in paratenic or intermediate hosts, such as rodents.

What is unique about the lifecycle of Toxascaris leonina compared to other ascarids?

- No tracheal migration.

- No in utero infection.

- No lactogenic transmission.

What is the geographic distribution of Toxascaris leonina?

- More common in northern-temperate regions.

- Higher prevalence noted in northern Ohio and other northern states.

In which hosts are co-infections with Toxascaris leonina and other Toxocara species documented?

Wild canids and felids.

Where is Toxascaris leonina frequently found outside of domestic settings?

In exotic felids in zoological collections.

How do Toxascaris leonina eggs appear in fecal examinations?

- Round to slightly oval.

- Smooth shell without the sticky albuminous coat of Toxocara.

- Light, translucent single-cell embryo, often dividing at room temperature.

- Size: 85 to 90 μm (average 85 μm diameter).

What is the clinical presentation of Toxascaris leonina infection?

Worms in feces or vomitus of the infected host.

What is the common name for Baylisascaris procyonis?

Raccoon roundworm.

How does the size of Baylisascaris procyonis worms compare to Toxocara canis and Toxocara cati?

Baylisascaris procyonis worms are much larger, with males measuring 9-11 cm and females 20-22 cm, though their eggs are smaller.

What is unique about the cervical alae of Baylisascaris procyonis?

They are inconspicuous or vestigial.

What are the two types of life cycles for Baylisascaris procyonis?

1. Direct life cycle: Ingestion of larvated eggs.

2. Facultative indirect life cycle: Ingestion of paratenic or intermediate hosts like rodents.

How can raccoons become infected with Baylisascaris procyonis through the direct lifecycle?

- Ingesting larvated eggs from contaminated fur, communal latrines, or dens.

- Ingesting eggs adherent to their mother's fur or teats.

How many eggs can an adult female Baylisascaris procyonis produce daily?

100,000 eggs per day, with an egg production rate of 20,000-26,000 eggs per gram (EPG).

What is the prepatent period for Baylisascaris procyonis?

50 to 76 days post-infection.

What are the important lifecycle differences for Baylisascaris procyonis in its definitive host?

- No tracheal migration.

- No in utero infection.

- No lactogenic transmission.

What is unique about Baylisascaris procyonis in intermediate hosts?

- Larvae exhibit aggressive somatic migration.

- Larvae continue to grow in size within the host.

- Larvae are neurotropic, causing damage to the central nervous system.

What is the distribution and prevalence of Baylisascaris procyonis in raccoons?

- Juvenile raccoons: >90% prevalence (direct infection from eggs).

- Adult raccoons: 37-55% prevalence (infected from larvae in tissues of prey or carrion).

What is the prevalence of Baylisascaris procyonis in nuisance raccoons in Atlanta residential neighborhoods?

22%

What other animals can serve as hosts for Baylisascaris procyonis?

Raccoons, skunks, badgers, martins/fishers, bears, marmots, and ground squirrels.

How many clinical cases of Baylisascaris procyonis have been reported in candids?

At least 12 cases have been reported, though likely underrepresented

Are there any overt clinical signs of Baylisascaris procyonis infection in raccoons?

No, raccoons show no overt clinical signs.

What is the clinical significance of Baylisascaris procyonis in paratenic hosts?

Causes clinical CNS disease and mortality in >130 species.

Non-specific clinical signs.

What are the key features of Baylisascaris procyonis eggs on fecal examination?

- Sub-spherical to slightly oval shape.

- Thick albuminous shell with finely pitted surface.

- Golden brown color.

- Dark single-cell embryo.

- Size: 63-88 μm by 50-70 μm (average 65 μm diameter).

How can Baylisascaris procyonis eggs be differentiated from Toxocara canis eggs?

- B. procyonis eggs are smaller (average 65 μm) with a golden brown color.

- T. canis eggs are larger (~85 μm) with a dark brown embryo.

What is Visceral Larval Migrans (VLM)?

Somatic migration of Toxocara larvae through organs like the liver, kidney, and lungs.

What age group is most affected by Visceral Larval Migrans (VLM)?

Younger children aged 2 to 7 years.

What are the clinical symptoms of VLM?

- Abdominal pain.

- Headache.

- Weakness and lethargy.

- Fever.

- Coughing, asthma, pneumonia.

How severe are most cases of VLM caused by Toxocara canis?

Most cases are mild with low morbidity and no mortality.

How is VLM diagnosed?

By Toxocara-specific IgG serologic assay.

What factors increase the risk of VLM according to NHANES data?

Lower household education (OR 2.2).

Poverty (OR 1.5).

Dog ownership (OR 1.2).

How can zoonotic toxocariasis be prevented in puppies?

Deworming at 2, 4, 6, and 8 weeks of age and monthly for the first year of life.

What role do monthly heartworm drugs play in prevention?

Most monthly heartworm drugs also protect against Toxocara infections.

What are prevention steps for adult cats?

Adult felines should be dewormed at regular intervals.

What measures can reduce environmental contamination with Toxocara eggs?

- Removing feces from yards and play areas.

- Keeping sandboxes covered when not in use.

- Washing hands after pet contact.

- Cleaning dogs promptly if they roll in contaminated areas.