It was decided during the discussion on Information Exchange that a small committee should draft a classification of Theileria parva reactions in cattle. This classification could then be used in reporting experiments or trials so that a generally accepted description of disease reactions is used and so that the interpretation of results from different studies by different authors is made easier.
The following clinical and parasitological parameters are used routinely in describing T. parva reactions:
Clinical
· fever, a rectal temperature greater than 39.4 °C associated with schizont parasitosis is considered a febrile reaction· condition, general appearance of the animal, respiratory rate and consistency of faeces
· lymph node enlargement associated with hyperplasia, parasitosis and fever
· lacrimation and/or corneal opacity
· white blood cell count
· time to death or recovery
Parasitological
· prepatent period to detection of schizonts
· dissemination of schizonts
· degree of schizont parasitosis
· duration of schizont parasitosis
· prepatent period to detection of piroplasms
· piroplasm parasitaemia
· duration of parasitaemia
Broad classifications of reactions have been attempted using combinations of these parameters. A generally accepted and recommended classification is as follows:
· No reaction or no apparent reaction: no parasites are detected and no clinical signs are apparent.· Mild reaction: few schizonts are detected, no fever occurs or fever persists for less than four days. The animal is otherwise clinically normal and recovers.
· Moderate reaction: schizonts are detected, fever persists for longer than four but less than nine days. The animal shows mild and transient clinical signs and recovers.
· Severe reaction and recovery or death: schizonts are detected, fever persists for eight days or longer and the animal has obvious clinical signs of theileriosis. The animal may recover from a severe reaction but usually dies.
Schizont parasitosis should not be used alone to classify reactions because a direct correlation between parasitosis and the severity of disease is not always found. This is particularly true of T. p. lawrencei and T. p. bovis infections. Moreover, the estimation of schizont parasitosis is subjective and may also reflect a variation in the distribution of schizonts within and between lymph nodes.
Animals with a severe reaction should be treated to avoid unnecessary suffering or death. These cases can be recorded as severe reactions and/or as death.
