Anaplasma infection in cows is most commonly seen in which age group?

• A. 0-1 year
• B. 2-4 years
• C. 5-7 years
• D. Adults over 8 years

Answer: (B)

Anaplasma marginale infection in cattle tends to cause clinically noticeable disease most often in animals that are past the neonatal period but not very old. Calves under a year usually have maternal antibodies and milder or subclinical infections, so they’re less likely to show obvious illness. In very old cattle, prior exposure and acquired immunity, along with management practices, often reduce the chance or severity of clinical disease. The two- to four-year-old group sits in the sweet spot: their immune system is mature and they have had enough opportunity for vector exposure to permit meaningful parasitemia, but they haven’t yet developed strong, lasting immunity or management-related protection. When infection becomes evident, these animals commonly show anemia and related signs, making this age range the one most frequently seen with clinical anaplasmosis.