Introduction
Ostertagia in animals is a genus of parasitic nematodes that primarily affect ruminants, causing severe parasitic gastritis. This condition is particularly prevalent in temperate climates and subtropical regions with winter rainfall.
Hosts and Site of Infection
Hosts: Ruminants (Cattle, Sheep, and Goats)
Site of Infection: Abomasum
Common Species
Ostertagia ostertagi – Cattle
Teladorsagia circumcincta – Sheep and Goats
Ostertagia trifurcata – Sheep and Goats
Minor species include O. lyrata, O. kolchida (cattle), and O. leptospicularis (cattle, sheep, and goats).
Distribution
Ostertagia species are distributed worldwide, with O. ostertagi being particularly significant in temperate climates.
Morphology
Adult worms are slender, reddish-brown, reaching up to 1 cm in length. They reside on the abomasal mucosa and can be difficult to detect without close inspection. Larvae develop within the gastric glands and are only visible microscopically.
Life Cycle
Ostertagia ostertagi follows a direct life cycle:
Eggs are passed in feces and hatch into first-stage larvae (L1) in the environment.
Larvae develop into the infective third stage (L3) under favorable moist conditions.
Ruminants ingest L3, which then exsheath in the rumen and migrate to the abomasum.
Two parasitic molts occur before the larvae emerge as adults after approximately 18 days.
Under certain conditions, larvae may enter an arrested (hypobiotic) state in early L4 for up to six months.
Pathogenesis
Ostertagia infections cause significant biochemical and pathological changes in the abomasum:
Destruction of parietal cells leads to a rise in abomasal pH (up to 7.0), impairing digestion.
Leakage of pepsinogen into circulation results in elevated plasma pepsinogen levels.
Protein loss into the gastrointestinal tract leads to hypoalbuminemia and submandibular edema.
The abomasal mucosa thickens, forming nodules, and can resemble “morocco leather” in severe cases.
Clinical Signs
Ostertagiosis occurs in two clinical forms:
Type I Ostertagiosis (Summer)
Affects calves during their first grazing season (July-October in the Northern Hemisphere).
Symptoms: Profuse, bright green diarrhea, weight loss, inappetence.
High morbidity (>75%), but low mortality with prompt treatment.
Type II Ostertagiosis (Winter-Spring)
Affects yearlings due to arrested larvae from the previous autumn.
Symptoms: Intermittent diarrhea, anorexia, thirst, dull coat, and rapid weight loss.
Lower prevalence but high mortality if untreated.
Epidemiology
The epidemiology varies based on climate and herd management practices:
Dairy Herds: Overwintered L3 can cause early-season infections, with peak contamination occurring mid-summer.
Beef Herds: Infection risk depends on calving season; spring-born calves have lower exposure compared to autumn-born calves.
Subtropical Regions: Outbreaks of Type I disease occur towards the end of winter, with Type II cases arising in late summer or early autumn.
Economic Impact
Ostertagia infections significantly affect livestock production:
Reduced weight gain and poor feed conversion rates.
Decreased milk yield in lactating cows.
Increased veterinary costs due to anthelmintic treatments.
Treatment and Control
Effective treatment and control strategies include:
Anthelmintic Treatment:
Benzimidazoles, macrocyclic lactones (ivermectin, doramectin), and imidazothiazoles (levamisole) are highly effective against both adult and larval stages.
Targeted deworming at critical times, such as pre-grazing, mid-season, and pre-housing, helps break the parasite’s life cycle.
Resistance management strategies, such as rotating drug classes and using combination treatments, reduce the risk of anthelmintic resistance.
Grazing Management:
Rotational grazing minimizes reinfection by preventing buildup of infective larvae in pastures.
Mixed-species grazing can help reduce parasite burden, as some species act as dead-end nematode hosts.
Nutritional Support:
Providing high-protein diets helps counteract protein loss due to parasitism.
Supplementing with minerals such as cobalt, copper, and selenium boosts immune function and resilience to infection.
Integrated Parasite Control:
Combining anthelmintic treatment with pasture management and selective breeding for parasite-resistant animals enhances long-term control.
Regular fecal egg counts help monitor parasite loads and inform treatment decisions.
Conclusion
Ostertagiosis remains a major challenge in ruminant health worldwide. Implementing strategic anthelmintic treatment, proper grazing management, and nutritional support can minimize economic losses and improve animal welfare.
FAQ’s
What animals are affected by Ostertagia?
Ostertagia primarily infects ruminants, including cattle, sheep, and goats. The most common species are Ostertagia ostertagi in cattle and Ostertagia circumcincta in sheep and goats.
2. What is Ostertagia’s predilection site?
The abomasum is the primary site of infection. Larvae embed in the gastric glands, while adults reside on the mucosal surface.
3. What are the symptoms of Ostertagia infection?
Symptoms include diarrhea, weight loss, poor growth, and reduced appetite. In severe cases, animals may develop a “bottle jaw” due to fluid accumulation.
4. How is Ostertagia diagnosed?
Diagnosis involves clinical signs, fecal egg counts, plasma pepsinogen levels, and post-mortem examination of the abomasum.
