AFRICAN REDWATER – THE DISEASE DEVELOPMENT PROCESS

Below is an example of the disease development of a tick-borne blood parasite that causes destruction of red blood cells leading to blood loss.

START OF INFECTION

The blood parasite (Babesia bigemina ) is transmitted by the nymph and adult stages of the blue tick when it sucks blood from the animal.

The blood parasite will enter the small blood vessels in the skin with the spit (saliva) of the tick when it sucks blood. It will then enter a red blood cell where it will grow and divide.

In this process, it will destroy (burst) the red blood cell, and the two parasites formed will now enter two new red blood cells.

Initially, only a very few red blood cells will be infected (fewer than one in 100).

WEEK 1 – 2

For the next two weeks, the animals will show no sign of disease and will behave, eat and walk normally.

Over these two weeks, the blood parasites will multiply and infect more and more red blood cells. Infected red blood cells burst, leading to blood loss (anaemia).

The liver or kidneys must dispose of the red content of the burst red blood cells. The animal’s own immune system now starts to react against the infection, giving rise to a fever.

AFTER 2 WEEKS

Infected cattle suddenly develop general signs of disease: They stop eating and chewing the cud, heads and ears hang and they become reluctant to move. More specific signs such as difficult or faster breathing and red-brown urine become apparent.

The animal’s fever will rise to over 40°C at least two days before visible signs of disease appear.

The animal copes with the blood loss up to the point when there are too few red blood cells left to carry enough oxygen to the rest of the body cells.

The animal will show sudden weakness and when examined, the inner eyelid will be white. The animal normally dies within 24 hours after advanced signs of disease.