Ticks are one of the most significant disease carriers affecting livestock in southern Africa, posing a constant threat to animal health, farm profitability and even human safety. Charl van Rooyen asks Dr Tom Strydom and Dr Faffa Malan how diseases spread through different tick species, how their life cycles influence infestation levels and why effective control remains a critical challenge for livestock producers.
Which diseases are transmitted by ticks?
Hard ticks are, economically speaking, the most far-reaching external parasites of production animals in tropical and subtropical regions. Livestock production is the largest farming sector in southern Africa, and cattle farming is the most important, despite the harsh climate with its sparse and unpredictable rainfall. But it is not only the climate that hampers farming; pests such as external parasites do too.
It is estimated that 80% of the world’s roughly 1.58 billion head of cattle are adversely affected by ticks (Statista, 2024). They are therefore a serious hazard to successful animal production.
Ticks pose various threats: they carry diseases, some fatal, transmit toxins, cause anaemia and damage hides and skins.
Ticks with long mouthparts, such as the bont tick and the bont-legged tick, cause great economic losses to livestock farmers because they sometimes damage the skins or hides to such an extent that marks or holes occur. As a result, the value of such hides or skins is reduced when they are sold.
The wounds they cause sometimes become septic and result in abscess formation. This can also lead to screwworm infection and mastitis in cows.
As blood-suckers, ticks can cause anaemia in cattle during severe infestations, resulting in weight and production losses.
They are also associated with certain animal diseases, such as redwater (babesiosis), heartwater and gall sickness (anaplasmosis), because ticks are carriers of the organisms that cause these diseases. In some species, the toxins they transmit in their saliva cause diseases such as sweating sickness, Karoo paralysis and spring lamb paralysis.
Ticks also carry organisms that cause biliary fever – a disease caused by the parasite Babesia canis rossi, commonly known as tick bite fever – in horses and dogs.
Humans can contract Crimean-Congo haemorrhagic fever, which is a viral disease, from the bite of a tick. In this case, the culprit is an infected bont-legged tick. Humans can also contract tick bite fever, which is transmitted by several tick species.
If a dog is bitten by the bont-legged tick, a large wound sometimes develops on its skin at the site of the bite.
Ticks are divided into three categories according to their life cycles, namely one-, two- or three-host ticks.
One-host ticks
All three life stages of the tick (larva, nymph and adult) occur on the same host. This category is represented by the blue tick, previously thought to be a Boophilus sp., but now considered a Rhipicephalus sp., which is a carrier of redwater, gall sickness and tick bite fever in humans.
Its life cycle takes about two months to complete, but development from larva to engorged female takes only three weeks.
When a female is engorged, she falls off the host and lays between 2 500 and 4 500 eggs. The eggs hatch after three to eight weeks – a larva with six legs emerges from the egg and climbs up a grass stalk.
While cattle graze, larvae climb onto them and suck blood for seven days. They then moult and a nymph emerges, still on the animal. They suck blood for another seven days, moult, and then adult females and males emerge. The ticks mate and the female sucks so much blood during the last day or two of the life cycle that she is easily visible – this is where the name “blue tick” comes from.
Professor Emeritus Ivan Horak made the following calculation: if 68 fully engorged females can be counted on an animal with the naked eye, this number represents only a seventh of all the females on the animal, so there are, in fact, 476 female ticks on the animal. The males live on the animal for a longer period (sometimes weeks). There are two males for each female, so on the hypothetical animal above there would be 952. Thus, in total, there are 1 428 adult ticks on the animal, two nymphs for each (2 856 nymphs) and two larvae for each nymph (5 712 larvae).
So, for the 68 ticks that can be seen with the naked eye, there will be about 10 000 ticks in various developmental stages on the animal.
In warmer, humid areas they occur throughout the year, mainly on cattle, but also on horses, donkeys, sheep and goats.
Two kinds of blue tick are carriers of redwater: one that transmits African redwater (Rhipicephalus decoloratus) and one that carries African and Asiatic redwater (Rhipicephalus microplus).
In southern Africa, intensive dipping programmes were enforced by the State up to the 1960s. As a result, blue ticks and redwater were effectively controlled. After that, there was a relaxation of control measures. At the same time, resistance to acaricides in the dips began to build up in ticks.
Since then, losses resulting from redwater have begun to increase again.
Two-host ticks
The two juvenile stages (larvae and nymphs) occur on the same host (for example, cattle, birds, game and rodents). The adult stage occurs primarily on cattle, horses, sheep, goats and larger game animals.
These are the red-legged and bont-legged ticks. Their life cycle is longer – three months compared with the one-host tick’s 21 days. The female red-legged tick (Rhipicephalus evertsi evertsi), the juveniles of which often attach in the animal’s earor under the tail, falls off when she is engorged and lays about 7 000 eggs on the ground.
The larvae that hatch climb onto the host (cattle, rodents or birds), where they suck until they are engorged with blood. They then moult to become nymphs, which engorge with blood before falling off.
They climb onto the next host, suck blood until engorged, and become males and females. They mate, the females suck a lot of blood and then fall off to lay eggs, and so the cycle continues.
The red-legged tick is the carrier of biliary fever in horses, East Coast fever and redwater in cattle, and tick bite fever in humans. They prefer to attach to the tail switch, feet and under the tail. The female lays about 5 000 eggs. Bont-legged ticks (Hyalomma spp.) produce a toxin that causes sweating sickness in calves. They have long mouthparts that can damage the animals’ hides.
Secondary infection sometimes occurs, causing bacterial abscesses, foot rot and teat loss in cows, which can result in mastitis. Blowfly maggots may appear in infected areas.
Bont-legged ticks have a similar life cycle. Adult ticks are found mainly on the tail switch and under the tail.
Ticks occurring between the claws of sheep and goats can cause severe lameness.
Three-host ticks
All three stages of these ticks occur on different hosts. Some of the best-known ticks in this group are the bont tick, the brown ear tick and the Karoo paralysis tick.
The engorged female falls off its host and lays a clutch of eggs. The larvae that hatch climb onto a host, suck blood until they are full and then fall off. These then moult before climbing onto the next host as nymphs. The nymphs also suck blood until they are engorged, then drop off, moult and climb onto another host as adults.
The life cycle of the bont tick, or heartwater tick (Amblyomma hebraeum), takes about five months to complete. A female can lay up to 18 000 eggs. The life cycle of the Karoo paralysis tick (Ixodes rubicundus) takes 24 to 35 months to complete, and the females lay about 2 000 eggs. The life cycle of the brown ear tick (Rhipicephalus appendiculatus) takes eight months to two years to complete, and each female lays about 5 000 eggs.
The favourite attachment site of the larvae of Rhipicephalus appendiculatus is the skin of an animal’s head, neck, dewlap and legs; the nymphs prefer the neck and base of the ears. The adult ticks prefer the belly, inside the ears and the neck.
The bont tick is the carrier of the organisms that cause heartwater. This ticck has well-developed mouthparts that cause painful wounds, which can lead to abscess formation and damage to the hide.
The brown ear tick prefers high-rainfall areas and attaches primarily to the animal’s ear. In severe infestations, they can cause such extreme damage that the ears fall off. They also attach to the skin around the eyes, cheeks, topline and neck.
This tick carries the organism that causes Corridor (buffalo) disease and East Coast fever. The ticks can cause damage to the ears, as well as tick toxicosis.
