The term redwater (babesiosis) is a generic term. It is thus important to distinguish between two diseases: African redwater and Asiatic or European redwater.
Redwater disease in cattle is caused by a protozoan blood parasite in the erythrocytes (red blood cells).
Two species of the pathogenic blood parasite occur in South Africa.Babesia bigemina causes African redwater, while Babesia bovis causes Asiatic or European redwater.
Cattle infected with the parasites remain carriers for considerable periods, and carriers have long-term immunity against redwater. Animals that have recovered from African redwater have a degree of immunity against Asiatic or European redwater, although the converse is not the case.
To protect cattle against serious disease and mortality caused by the redwater parasite, less virulent vaccine strains of the parasite in the form of live blood vaccines are used to immunise cattle against both types of the disease.
Geographical distribution Redwater is widespread throughout and endemic to large areas of South Africa, excluding areas of very low rainfall where tick populations are low. Its distribution is connected to tick-transmitted gallsickness (anaplasmosis) in cattle, although gallsickness has a wider distribution as it is also transmitted by biting flies.
African redwater has the wider distribution, absent only in arid parts of South Africa such as the Northern Cape and Great Karoo, corresponding with the distribution of two blue tick species (see map 1). Asiatic redwater occurs in most of Limpopo, Gauteng, Mpumalanga, KwaZulu-Natal and along the Eastern Cape coast and the Western Cape (see map 2). Its distribution range is expanding due to the expanding distribution of the ticks as intermediate hosts.
African redwater is transmitted through the bite of two species of blue tick; the Asiatic blue tick Rhipicephalus (Boophilus) microplus and the African blue tick Rhipicephalus (Boophilus) decoloratus. Both are single host ticks. The red-legged tick Rhipicephalus evertsi can also transmit the parasite but its role in transmission is more limited.
The blue tick favours traditionally hot, humid conditions and is sometimes absent in the more arid parts of the Western and Northern Cape, western Free State and higher-lying parts of the Drakensberg and Lesotho. Asiatic redwater has a more restricted distribution as it is only transmitted by the Asiatic blue tick R. microplus, which occurs in high rainfall regions including the Eastern Cape, KwaZulu-Natal and the eastern parts of Mpumalanga.
Redwater is only transmitted by ticks, and the distribution of African and Asiatic redwater is closely associated with the distribution of their respective tick hosts.
- Transmission of African redwater
Ticks (vectors) are infected with the disease when feeding on an infected or carrier animal. The disease transmitted from the larval stage via the nymph stage to the adult. Infected females dropping off the host animal carry the disease through the egg stage (eggs are laid on the ground) and then to the next generation of larvae in a process called trans-ovarian transmission. The nymphs and adults of the next generation transmit the disease to susceptible host animals.
- Transmission of Asiatic/European redwater
The course of the disease is similar to that of African redwater. The infected female transmits the disease transoviarially to her progeny, although only the larval stage of the tick transmits the disease to cattle. Although the larvae no longer carry the disease after transmitting it, the next generation of nymphs is again infected by feeding on a carrier bovine, which once more transmits the disease to adult ticks.
In areas normally free of redwater, climatic conditions favouring tick survival may promote outbreaks of the disease should ticks be brought into the area. Infection of an unborn calf may lead to abortion or the death of the calf shortly after birth.
Occurrence, immunity and resistance
Although all cattle breeds are susceptible to redwater, Zebu and Sanga cattle are more resistant than European breeds.
After a single exposure to redwater, most animals develop a long-term immunity, which may be life-long.
Redwater often exhibits a pronounced seasonal nature, with outbreaks habitually occurring during the hotter summer and autumn months. This increased incidence of the disease corresponds with an increase in the number and activity of ticks during that period.
- Calf susceptibility
Calves younger than two months, born from dams that have not been exposed to the redwater parasite and have no immunity against it, are susceptible to infection. From about two months, calves often have a non-specific natural immunity to redwater that persists until they are about eight months old. Calves born to cows that are immune to redwater are protected through colostrum immunity (passive immunity) until the age of about two months.
After this, they are protected for a further four to six months by a non-specific natural resistance to the disease that gradually decreases as the animal ages. This non-specific resistance is probably at its strongest at around six months, but calves of up to nine months seldom show disease symptoms and develop only a mild form of the disease.
However, the immunity of calves up to eight or nine months is not absolute. A calf with a sub-optimal immune system, including those suffering from diseases such as bovine viral diarrhoea and enzootic bovine leucosis, is malnourished or under a high endoparasite or ectoparasite load, and can be susceptible to redwater.
It should be noted that even older animals previously exposed to the disease and developing an immunity against it, can become susceptible during conditions of high stress. Around calving time, the cow’s resistance against disease decreases and serious cases of redwater are not uncommon. In fact, the disease may be far more serious in adult animals contracting it for the first time. In such cases, disease and mortality can lead to serious losses.
In an area with a sufficiently high population of infected ticks, all calves should become infected at an age of up to nine months. Therefore, as calves become ‘naturally immune’ at an early age, no outbreak of the disease should occur among adult cattle in such an area.
When the incidence of infected ticks in an area is too low, whether due to tick control or natural factors such as drought, some calves are susceptible to redwater. All calves are therefore not exposed to infection and an outbreak of the disease can be expected the following year when they are more susceptible.
Although calves should preferably be naturally immunised through tick-transmitted infection, the influence of natural factors such as rainfall on tick populations cannot be controlled. For this reason, redwater immunisation is usually used to supplement natural infection to protect animals that have not become infected as calves against the serious consequences of natural infection at a later stage.
Should cattle in a redwater area be moved from one farm to another, or from one camp to another, they can also contract redwater. Always be aware of the danger of a redwater outbreak when moving cattle. Safeguard them before moving them with prophylactic (preventative) injections of imidocarb (Imizol) or diminazene (Berenil), according to prescription.
Cattle usually show clinical symptoms of redwater around two weeks to three weeks after exposure to infected ticks. Symptoms are usually characterised by high fever (>40,5°C), light to dark red urine – hence the name – anaemia and sometimes jaundice, as well as depression and a lack of appetite.
African and Asiatic redwater symptoms are similar and distinction is therefore difficult. The disease progresses rapidly and animals may die if not treated timeously. A fever reaction (a body temperature of 40°C to 41,5°C in the morning) is usually present for a few days before other symptoms appear.
This is followed by poor appetite, listlessness, weakness and a reluctance to move. Anemia and even jaundice follows, especially in more advanced cases. A dry nose, dull hair coat and diarrhoea are less specific symptoms.
Urine is not always discoloured. Nervous symptoms, caused by the accumulation of parasites in the blood vessels of the brain, such as increased or reduced reaction to stimuli, poor coordination, muscular tremors, convulsions and even coma may occur in advanced cases.
When these occur, the disease is called cerebral redwater and can be confused with heartwater, among others. In serious cases, mortality is high, despite good professional treatment.
In many cases of Asiatic redwater, the animal may go into shock due to the accumulation of the parasites in peripheral (superficial) blood vessels. This leads to a shortage of oxygen in the organs, organ failure and eventually death.
It is believed that the greatest cause of cattle mortality in South Africa is Asiatic redwater.
Consult a vet for a provisional diagnosis – he will perform a blood and/or brain smear, or consider disease symptoms and/or post-mortem lesions.
Do not stress sick animals. Ensure they are protected from inclement weather and provide free access to fodder and clean water. Treat the animal as soon as possible after observing disease symptoms and/or a blood smear confirms a positive diagnosis.
Several redwater remedies can be obtained without prescription; including diminazene (Berenil RTU, G2702; Dizene, G2611; Rednil, G3911; Veriben, 3827) and imidocarb (Imizol, G0831). Establish dosage according to the live weight of the animal and ensure the animal is treated according to the prescription – using a dose of diminazine lower than the prescribed dose can lead to the parasites developing a resistance to the active ingredient, and over-dosing can be toxic.
If treated timeously, the animal should recover.
However, in advanced cases, the prognosis and the chance of recovery are poor. In such cases, supportive vet treatment, which may even include a blood transfusion, may be life-saving. Consult a vet for appropriate treatment.
Redwater can be controlled by keeping cattle free of ticks. Resistance to acaricides has dramatically increased in local tick populations over the years and on some farms they are no longer effective. The ideal is to maintain a balance of tick exposure that enables the development of natural immunity, and to ensure that cattle are not detrimentally affected by ticks. Where macrocyclic lactones are used in blue tick control, the larvae can still transmit Asiatic redwater before they are killed. Consult your vet regarding this.
In redwater-endemic areas, cattle must adapt to the conditions, and the ideal is to strive for endemic stability. Inoculating animals with blood vaccines (African and/or Asiatic redwater vaccine) affords good protection and is recommended. The blood vaccine for both is provided in frozen form.
- Immunisation and exposure
Calves must be inoculated or exposed to the disease between three and nine months. The level of infection in blue tick populations on farms with redwater is very low (0,04% for Asiatic redwater and 0,23% for African redwater), and large populations of the various blue tick species are required on calves to ensure exposure to natural infection at an early age.
Redwater vaccination reactions usually develop between one week and three weeks after inoculation or infection: African redwater symptoms appear within seven days, with Asiatic redwater symptoms appearing 10 days to 12 days after infection.
Symptoms vary from an increase in rectal temperature to serious clinical signs in susceptible ‘unsalted’ animals. Young calves show the highest resistance and seldom develop serious symptoms after infection or inoculation, but in susceptible adult cattle serious clinical symptoms may appear.
Calves younger than two months should not be inoculated, as the passive immunity obtained from the dam may influence the effectiveness of the vaccine. A vaccinated animal must be regularly exposed to tick bites containing the normal wild redwater parasite strains in order to boost immunity.
- Administering the blood vaccine
Live redwater vaccines (African and Asiatic strains) may be administered together. Animals treated with imidicarb must not be vaccinated with Asiatic redwater vaccine within four months of treatment. The same applies to diamazine, its period being two months. These drugs will block infection for the respective periods and prevent immunisation.
Once the animals have been immunised, disease-specific drugs will not suppress the animal’s immunity. Only conditions that affect the immune system can make the animal susceptible to the disease once more. The vaccine must be stored or transported on dry ice (-80°C) or in liquid nitrogen (-196°C). The dose is 1ml, administered intramuscularly, irrespective of the age or size of the animal. The frozen vaccine may be thawed slowly, or rapidly in lukewarm water (40°C).
- Slow thawing
Place the frozen vaccine directly on melting dry ice and transport it to the work station. Only thaw enough to be used immediately after thawing – it must be used within four hours of being removed from the dry ice or liquid nitrogen. Once the vaccine has thawed, it cannot be refrozen. A vaccine that has thawed during transport or storage must not be used. Never store frozen vaccine in a conventional freezer (-10°C to -18°C).
Details on vaccine use are contained in the vaccine’s instructions; study the contents each time the vaccine is administered, as the prescriptions and instructions may change from time to time. Pregnant heifers and cows may abort should serious vaccine reactions occur.
Redwater vaccine may be administered together with anaplasmosis blood vaccine or any other vaccine, except heartwater vaccine.
Steps to be taken during an outbreak will mainly depend on herd size, the manpower and facilities available and the cost of the remedies. A vet should be consulted for details on measures to limit losses. Cattle that have been vaccinated as part of a treatment programme must be kept clean of ticks for six weeks.
Testing for susceptibility
Blood samples can be serologically tested to establish whether the herd is susceptible to African and/or Asiatic redwater. Should the herd be susceptible, the correct redwater immunisation programme can be followed.