Epidemiology of bovine ostertagiosis

Question 1

Define epidemiology

Answer 1

The pattern of disease within a population

Question 2

Bovine ostertagiosis affects cattle at what ages?

Answer 2

• Dairy replacement calves

- First grazing season

Question 3

What factors may affect epidemiology of ostertagiosis?

Answer 3

• Immune status of the cattle
• Numbers of L3 on pasture
• Temperature and humidity
• Previous pasture usage, rotation
• Worming

Question 4

Development of the pre-parasitic stages requires what conditions?

Answer 4

Temp of more than 10 degrees
Humidity and rainfall
Dispersion from the faecal pat

Question 5

What factors help and determine the survival of L3?

Answer 5

• Being ensheathed gives them an extra level of protection
• Temperature (tolerates cold, hates heat)
• Desiccation is lethal so need adequate moisture levels
• Food reserves

Question 6

Which host factors affect the epidemiology of Ostertagia?

Answer 6

• age
• immune status
• over dispersion – small proportion of the host population carries the majority of the parasite population

Question 7

Describe the pattern of Bovine ostertagiosis in May

Answer 7

• First season dairy calves turned out
• They begin to graze and ingest L3
• No disease as L3 levels are too low

Question 8

Where do the L3 in may come from?

Answer 8

• field used the previous year

- overwintered L3

Question 9

Describe the pattern of Bovine ostertagiosis in June

Answer 9

• overwintered L3 die off but animals are already infected
• L3 mature over the 3 week PPP
• eggs produced onto pasture
• ambient temperatures gradually start to increase, eggs start to develop, a higher temp = faster development

Question 10

Describe the pattern of Bovine ostertagiosis in July

Answer 10

• Eggs continue to develop on pasture

- Peak of L3 development in mid-july

Question 11

Describe the pattern of Bovine ostertagiosis in August

Answer 11

• large numbers of L3 develop in the abomasum of calves

- type 1 disease 3 weeks later

Question 12

Describe the pattern of Bovine ostertagiosis in Autumn

Answer 12

• after a dry summer L3 might be released from faecal pats by rainfall
• calves moved back onto contaminated pasture
• L3 on pasture are exposed to decreasing temperature’s which triggers L4 to hypobiose
• hypobiosed L4 accumulate in gastric glands

Question 13

Describe the pattern of Bovine ostertagiosis in late winter/early spring

Answer 13

• Larval development resumes
• simultaneous emergence of L5
• type II ostertagiosis
• severe clinical disease and high mortality

Question 14

Why is clinical disease less common in beef herds?

Answer 14

• Calves graze with immune mothers

- Autumn born calves may be at risk when turned out in the spring – graze and ingest overwintered L3

Question 15

What can be used to give a definitive Ostertagia diagnosis?

Answer 15

Raised plasma pepsinogen levels (from a blood sample) caused by damage to the gastric glands

Question 16

Why do we see type I ostertagiosis in August?

Answer 16

Due to a build up of L3 on pasture from eggs shed by calves infected by o/w L3 at the start of the season. Eggs develop in a temperature dependent way.

Question 17

Why do we see type II ostertagiosis in Feb/March?

Answer 17

Calves pick up infection in the autumn, Ostertagia ostertagi L3, exposed to drop in temperature before ingestion, hypobiose and emerge simultaneously in late winter, causing massive pathology in the abomasum.

Question 18

Why are spring born suckler calves less likely to develop type I ostertagiosis?

Answer 18

Spring born calves start grazing with their mothers.
Dams will eat majority of o/w L3 on pasture before the calves start to graze and take in significant amounts of grass. o/w L3 have died off by early June, when calves start to graze.

Question 19

What action would you take if called to a farm with yearlings suffering from type II ostertagiosis?

Answer 19

Treat them urgently with an anthelmintic that targets L4, L5 and adults - such as a macrocyclic lactone.