Exam 2 - Lecture 11

Question 1

Gastrointestinal Nematode Parasites of Domestic
Production Animals

Answer 1

-Cattle: Ostertagia spp., Type 1 Disease and Type 2 Disease

-Sheep, Goats, and
Camelids: Haemonchus contortus

-Other Trichostrongylid worms of lesser importance: Trichostrongylus and Cooperia

Question 2

Trichostrongylid Nematode Parasites of Cattle, Sheep, Goats, and Camelids

Answer 2

-Small gut‐dwelling nematodes

-No extensive tissue migration

-Simple, direct life cycle

-“Arrested Development” (aka Hypobiosis) as an important adaptation to survival and maintenance of parasite populations

-Primary target of producer initiated
parasite control programs

Question 3

Arrested Development

Answer 3

-Recently ingested pasture larvae enter the gut tissue, stop developing, and remain in juvenile state for several months

-Arrested larvae resume development when environmental conditions are favorable for parasite reproduction

-Adaptive strategy for survival of parasite populations: hostile or adverse environmental conditions and founding population to “seed” pastures each season

Question 4

Life Cycle Biology of Trichostrongylid
Parasites

Answer 4

-Adult worms live in the gut &
reproduce

-Eggs passed in feces

-Develop larvae and hatch

-Free living larvae develop to infective stage on pasture

-Sensitive to climatic conditions

-Animals become infected while grazing

-Pre‐patent period ~ 21 days from infection

Question 5

Diagnosis of Trichostrongylid
Nematodes

Answer 5

-Periodic (frequent) assessment of herd health: high FEC shedders, treatment efficacy, and occasionally “sick animals”

-Eggs (70‐90 x 40‐45) of all species are morphologically indistinguishable: attributed risk of parasite disease is by host species, and “the important parasite” for the host

-Diagnostic methods: fecal Flotation (semi‐quantitative) and McMasters Quantitative (Fecal Egg
Count Test)

Question 6

Thin‐shelled, morulated eggs on fecal examination

Answer 6

-Hookworm‐like (dogs, cats): Ancylostoma, Uncinaria

-Strongyle‐like (horses, pigs): Large Strongyles and Cyathostomins

-Trichostrongyle‐like (cattle, sheep, goats, camelids): Ostertagia, Trichostrongylus, Cooperia, and Haemonchus

-Host & Size!

Question 7

Ostertagia spp. Brown Stomach Worm

Answer 7

-Adult worms are parasitic in the abomasum
-Small worms, sexually dimorphic: males (6 to 7mm) and females (8 to 9mm), males w/ copulatory bursa (morphology of spicules are diagnostic)

-Direct life cycle w/ arrested development in gastric pits: pathologic significance and epidemiologic significance

-Highly pathogenic: type I disease, type II disease, and associated with tissue damage to abomasum

-Most economically significant parasitism of cattle

Question 8

Clinical Disease Spectrum

Answer 8

-Type 1 Disease: many worms acquired over short period of time, favorable environmental conditions, and usually young animals (1 st season on pasture)

-Type 2 Disease: occurs months after initial infection and older animals (2nd season on pasture)

Question 9

Type 1 Clinical Disease Southern Pattern

Answer 9

-Young cattle acquire substantial worm burdens
grazing pasture between October and March: favorable (medium temp/moisture) pastures

-Continuous infection while grazing, turn‐over in adult worm populations

-Ingested infective larvae begin to arrest in tissues April‐September: hostile (high temp/drier) pastures

Question 10

Type 1 Clinical Disease

Answer 10

-Larvae mature in gastric glands of the stomach

-Damage occurs when larvae leave glands to become adult worms and reproduce

-The process is continuous and cumulative

Question 11

Type 1 Ostertagiosis

Answer 11

-Characterized by:
-Profuse watery diarrhea (often bright green
from grazing lush spring pastures)
-Bottle jaw from tissue leaking and impaired digestive function
-Loss of appetite, failure to gain weight, loss of body condition
-Young animals, 1st season on pasture, are most severely affected

-Positive response to timely treatment

Question 12

Type 2 Clinical Disease Southern Pattern

Answer 12

-Infective larvae acquired during late spring months

-Larvae enter the gastric glands and remain
dormant

-Damage occurs when larvae leave the glands “en masse” during late summer‐fall months

-The process may be catastrophic or protracted

Question 13

Type 2 Clinical Disease

Answer 13

-Accumulation of large numbers of parasites over longer period of time when environment hostile to pasture larvae survival

-Older cattle (usually 2nd grazing season) clinical disease often associated with stress (nutritional, post‐calving, etc.)

-Clinical signs similar to Type 1 disease, but more severe, often results in high mortality

-Fecal exams likely negative, disease related to emergence of larvae and tissue destruction

-Generally poor response to worming

Question 14

Type 2 Ostertagiosis

Answer 14

-Characterized by:
-Brown watery diarrhea
-Loss of appetite & loss of body condition
-Rumen PH approaches neutral
-Negative fecal exams
-Older animals, 2 nd season on pasture, are most severely affected

-Poor response to treatment

-Diagnosis based on clinical signs & seasonal onset of disease from emergence of larvae

Question 15

Trichostrongylus sp.

Answer 15

-Common parasite in Cattle:
-Less Pathogenic
-Disease associated with large numbers (10,00 to 100,00 worms)
-Young and nutritionally stressed animals @ greatest risk

Question 16

Cooperia sp.

Answer 16

-Common parasite in Cattle:
-Disease typically associated with calves
-Associated w/ subclinical production
losses in ADG (cost of feeding to selling weight)
-~$75 increase/head in sale price
compared w/ non‐dewormed cattle

Question 17

Nematodirus spp.

Answer 17

-Common parasite in Cattle:
-Seasonal (spring) hatching concentrates infective worms
-Disease typically associated with calves in late spring

Question 18

Trichostrongylid Parasites of Cattle

Answer 18

-NAHMS statistical sampling of
88% of US beef inventory: cooperia most prevalent in 91% of all cattle by PCR and Ostertagia in 80% of cattle (PCR)

-Emerging drug resistance in Cooperia: dose limiting species w/ macrocyclic lactone drugs
-Suggestion that “pour‐on” ML use for fly & lice control has led to decreased efficacy

-Ostertagia still controlled effectively with Smart de‐
worming

Question 19

Anthelmintic Control of Parasites in Herd
Animals: Strategic de-worming

Answer 19

-Removal of parasites from the host by exploiting
their seasonal biology: targeting inhibited larval
stages (differential selectivity against inhibited larvae)

-Reduction of worm burdens by removal of accumulated adult parasites

Question 20

Anthelmintic Control of Parasites in Herd
Animals: Selective de-worming

Answer 20

-Removal of parasites from “selected hosts” within a managed population: allowing a portion of the total parasite population to survive & reproduce in the absence of drug selection
-“Refugia” parasites not subjected to drug selection
-Maintain genetic heterogeneity (susceptible & resistant genotypes)

-Host selection based on risk mapping individuals w/in the herd:
-Young vs. Older animals
-High Egg‐Count shedders
-Clinically ill vs. Asymptomatic animals

Question 21

Anthelmintic Control of Parasites in Herd
Animals: Not Mutually Exclusive

Answer 21

-Treat young animals, reduce adult worm burdens & disease potential @ high pasture infectivity (seasonal biology)

-Treat high FEC shedders to reduce pasture contamination

-Target inhibited larvae seasonally w/ effective drug to reduce overall or selected portion of parasite population (low pasture infectivity @ mid‐summer)

Question 22

Prevention & Control of Ostertagiosis (Part 1)

Answer 22

-Not feasible to eliminate parasites from cattle herds

-Goal is reduce pasture contamination and hazardous re‐infection

-Map disease risk in the herd:
-Type 1 Disease
-Young cattle (1 st season on pasture)
-Lack of previous exposure provides inadequate immunity
-Accumulate substantial worm burdens resulting in high fecal egg counts
-Environmental conditions favorable for larval development and high rate of parasite transmission

Question 23

Prevention & Control of Ostertagiosis (Part 2)

Answer 23

-Not feasible to eliminate parasites from cattle herds

-Goal is reduce pasture contamination and hazardous re‐infection

-Map disease risk in the herd:
-Type 2 Disease
-Older heifers (2nd season)
-Mass emergence of arrested larvae
-Fecal exams likely negative

-Treating “older” adult cattle with sub‐clinical
infection not practical, not cost‐effective, & may lead to drug resistance:
-Effective immunity
-Low worm burdens
-Low FEC

-Stocker’s & New Additions must be treated to prevent importation of “resistant” parasites, avoid hazardous contamination.