Parasites

Question 1

What is the prepatent period for large strongyles?

Answer 1

Ranges from 5.5 to 12 months

Question 2

What are possible sequelae of large strongyles?

Answer 2

L4 larvae migrate through the abdominal blood vessels (cranial mesenteric artery) and cause “verminous arteritis” and thromboembolism.

Question 3

What is important today about large strongyles?

Answer 3

Historically was an important cause of colic

Rarely seen today because of deworming strategies

Question 4

What do small strongyles do in the GI tract?

Answer 4

L3 larvae invade the mucosa of the large colon and become encysted

Question 5

What clinical signs do small strongyles cause once they leave their encysted stage?

Answer 5

Emergence of encysted L4 can cause colic, diarrhea, weight loss, colic, and rough hair coat

Question 6

What is the prepatent period for small strongyles?

Answer 6

Encysted forms may last 2 years or longer

Question 7

What anthelminthic choices are there for the encysted small strongyles?

Answer 7

Fenbendazole (double dose) and moxidection

Question 8

What do ascarids do to establish themselves in the host?

Answer 8

Eggs are very hardy. They migrate through the lungs after about a week causing cough and respiratory disease

Question 9

What clinical signs do ascarids cause?

Answer 9

Only in horses less than 2 years old

Weight loss, ill thrift, impactions in foals

Question 10

What is the prepatent period for ascarids?

Answer 10

10 to 15 weeks

Question 11

What anthelminthic concerns are there for ascarids?

Answer 11

Be very cautious with anthelminthics that paralyze or kill rapidly like moxidectin, ivermectin, and pyrantel. This could lead to impactions. Must be killed SLOWLY.

Question 12

What is different about diagnosing cestodes as compared to other parasited?

Answer 12

Because they shed intermittently, normal fecal floats are unreliable

Question 13

What is the intermediate host for cestodes?

Answer 13

Oribatid mites

Question 14

What clinical signs do cestodes cause?

Answer 14

Adult parasites reside at the ileocecal valve area

Cause colic, impaction, intussusceptions, ill thrift, and weight loss

Question 15

What anthelminthic choices are there for cestodes?

Answer 15

Only praziquantel is effective and approved. A double dose of pyrantel also works.

Question 16

What is the prepatent period for cestodes?

Answer 16

6 to 16 weeks

Question 17

What form of the botfly is in horses?

Answer 17

Only the larval form

Question 18

What clinical signs do botfly larvae cause?

Answer 18

Potential oral irritation with larval migration but disease due to bots is rare

Question 19

What is the prepatent period for botflys?

Answer 19

Remain in the stomach for many months. They pass into the manure, pupate, and emerge as adult flies

Question 20

What anthelminthic choices are there for botflys?

Answer 20

Ivermectin or moxidectin

Deworm in the late summer or fall

Question 21

Lets have a DTR with benzimidazoles

Answer 21

Example: Fenbendazole

Do not induce rapid paralysis or death

Double dose recommended for treatment of ascarids or encysted cyathostomins (5 day treatment for cyathostomins)

Question 22

Lets have a DTR with tetrahydropyrimidines

Answer 22

Example: Pyrantel

Causes an irreversible rigid paralysis

Only treats adult parasites

Double dose can be effective against tapeworm

Question 23

Lets have a DTR with macrocyclic lactones

Answer 23

Example: Ivermectin and Moxidectin

Acts on chloride channels to cause flaccid paralysis. Do not use for ascarids.

Can kill migrating parasites, encysted cyathostomin, lice, mites, habronema, draschia, etc.

Question 24

Lets have a DTR with isoquinolones

Answer 24

Example: Praziquantel (only type used in horses)

Only effective in tapeworms

Question 25

What are the main goals for a parasite program?

Answer 25

A. Minimize the risk of parasitic disease - Be okay with minimal levels B. Control parasite egg shedding C. Maintain efficacious drugs (decrease anthelmintic resistance(

Question 26

What are steps to dealing with parasites?

Answer 26

1. Determine the shedding status of adult horses - 20% of the horses in the herd shed about 80% of eggs - Horses with a FEC of < 200 EPG are low contaminators 2. Determine whether foals and weanlings have ascarids and/or ascarids 3. Evaluate anthelmintic efficacy using FECRT 4. Evaluate and monitor strongyle egg reappearance period after deworming

Question 27

What is a fecal egg count reduction test?

Answer 27

Used to determine if parasites are resistant to an anthelmintic Collect a sample for FEC prior to and 10-14 days after deworming Calculate the percent reduction for each horse and then the mean for all horses on the farm as an indicator of farm resistance

Question 28

How must you interpret a FECRT?

Answer 28

At the herd or population level and not based on an individual animal. Results will vary on an individual basis.

Question 29

What are the limitations of the fecal egg count testing

Answer 29

1. Does not accurately reflect the total strongyle or roundworm burden 2. Does not detect larval stages (migrating or encysted) 3. Tapeworm infections are often missed or underestimated 4. Pinworms are usually missed

Question 30

General principles for parasite control: Adult horses

Answer 30

1. One or two annual treatments for strongyles, tapeworms, bots with usually ivermectin or moxidectin with praziquantel 2. Additional treatments should target the horses with FEC > 200 EPG 3. Treat mainly during peak transmission like spring and fall 4. Include praziquantel for tapeworms at least annually if tapeworms are present in the area

Question 31

General principles for parasite control: Foals and weanlings

Answer 31

A. Minimum of four treatments in the first year of life B. First treatment at 2-3 months with fenbendazole (slow kill so they don’t get an impact ion) C. Second treatment just before weaning; can base drug choice on FEC D. Third and fourth treatments at 9-12 months , including praziquantel for tapeworms E. Yearlings and 2-year-olds should be treated as “high” shedders with 3-4 yearly treatments

Question 32

What are 3 scenarios in which gastrointestinal parasites could be present and causing weight loss, but the quantitative fecal egg count is negative?

Answer 32

1. Tapeworms and intermittent shedding 2. Encysted stage 3. Ascarids have a long pre-patent period