These blood-borne parasites are spread by the common tick, which results in peaks of the disease in association with peak tick activity in the spring and autumn. Cattle on farms with tick populations need to be monitored closely for redwater during these periods of high tick activity.

Cause

Redwater is mainly encountered in later spring, summer and early autumn as main tick activity occurs during the months of May/June and again in September/October. It is rare to see disease in calves less than six months old. The condition is more common on heavy land and in old pastures that have a butt of dead grass at the base of the sward and where there are rushes. The tick lives in this butt of grass during the winter months. During the active period they climb to the top of the grass and attach themselves to passing animals. When feeding the tick transmits the small protozoa into the blood and it is these small parasites which cause the breakdown of red blood cells in the blood. While cattle reared on the tick-infested pasture will develop natural immunity, newly purchased cattle are at extreme risk when moving on to infected pasture. Older stock never previously exposed to the tick are most at risk.

Symptoms

Once these parasites gain entry to the bloodstream of an animal lacking in immunity they invade the circulating red blood cells (RBCs). They multiply, leading to rupturing of the red blood cells, allowing the release of haemoglobin, which gives blood its red colour. This is excreted in the urine leading to red coloured urine, the most obvious sign of the disease. A clear indication is also that the urine will also be quite frothy once it is discharged on to the ground or pasture.

The disease progresses in stages if the animal is not treated. In the first 24-36 hours of sickness the animal will have a very high temperature (up to 42°C) and diarrhoea that may be passed in a thin, watery stream, described as a pipe-stem diarrhoea.

After 48 hours, the animal develops dry dung and constipation. The animal becomes progressively weaker, with ongoing blood loss. The animal will develop pale gums and eye colour (pale vulva in cows/heifers also) and a very fast, loud heart. The urine also tends to become darker with time, which is also a bad sign.

The animal will become recumbent towards the end and may develop jaundice (yellow colour to the eyes, gums and vulva). In advanced stage, the animal will collapse and become unable to stand. Death is inevitable without veterinary treatment as early as possible in the course of the disease.

Treatment

Where you suspect an animal to be suffering from redwater you should seek veterinary advice immediately.

In early cases, treatment involves the injection of imidocarb dipropionate (Imizol) under the skin as early in the course of the disease as possible. Laxatives such as treacle, epsom salts or liquid paraffin can be used to counter the constipation. Anti-inflammatories are indicated if there is a high temperature and antibiotics such as oxytetracyclines will also kill any secondary tick-borne fever infection that could be a complication

Later in the course of the disease, blood transfusion(s) are indicated and may be the only viable option to keep the animal alive long enough for the Imizol to kill the parasite and stop blood breakdown.

It is important to note that Imizol has a meat withdrawal period of 213 days while it has a milk withdrawal period of 21 days.

Prevention and control

Redwater is a tick-borne disease, so elimination of a habitat conducive to tick survival is the best way to prevent it. Ticks survive in rough grazing, especially where there is a heavy density of rushes, ferns etc. For this reason, improvement of pasture is a key issue to address. There are seasonal peaks in tick activity in April and September, but the condition occurs throughout the summer.

Recently purchased animals are most susceptible to redwater and should be kept off rough pastures during periods of greatest risk.

The use of ectoparasiticides such as pyrethroid pour-ons or avermectin pour-ons prior to risk periods will help to kill ticks and reduce exposure over time but they cannot be depended upon to prevent the disease. The use of injectable avermectins for worm control has led to a dramatic reduction in the prevalence of redwater in many areas. The use of Imizol at double the dose will give protection for four weeks and can be used at high-risk times of the year.