means that calves born of cows with good immunity have passive immunity (via colostrum) for the first 6-8 months of their lives; if they get vaccinated or infected naturally by ticks in this period often lifelong immunity occurs.
Susceptible animals occur when:
- Passive immune calves receive no booster infection or vaccination up to 8 months of age.
- Animals are moved between clean and contaminated regions.
- Total tick control is applied.
- Animals, especially calves in dairies, are kept indoors ie. with no tick contact and then released onto pastures at a few months of age only.
- Long periods of unusual weather cause an absence of contaminated ticks.
Weather ie. rainfall and temperatures determine the geographical distribution of tick population that transmit red water (see attached map).
Buying, selling and moving cattle also spreads the disease as tick populations hitch a ride from one farm or region to the next.
This is not a simple problem. Please contact your vet for further recommendations.