Can Sheep Get Sick From Tick Bites?

External parasites can quickly wreak havoc on sheep flocks. According to the scientific journal, Parasites & Vectors, approximately 13 percent of sheep farms reported tick presence. Although tick-borne illnesses aren’t well-studied among sheep (as, say, cattle and domestic pets), we do know that ticks cause adverse health effects in sheep and can lead to significant economic impacts for farmers.

Sheep can get sick from tick bites. Tick-borne diseases that affect sheep include louping ill virus, tick paralysis, relapsing fever, cowdriosis (heartwater), anaplasmosis, and parasitic illnesses. Secondary complications include pyemia, skin and ear infections, wool destruction, and anemia.

This article discusses tick-borne diseases in sheep, as well as their diagnosis and treatment. Additionally, it covers potential secondary complications caused by these tick-borne illnesses in ruminants. Read on to learn more.

Tick-Borne Diseases in Sheep

There are hundreds of tick-borne diseases found in sheep. Farmers and veterinarians consider certain diseases more critical than others due to their significant economic impact. This section dives into eight tick-borne illnesses found in sheep, their geographical distribution, symptoms, diagnosis, and treatment options. We’ll also briefly touch on sheep and Lyme disease at the end of this section.

Louping Ill Virus (LIV)

Louping Ill Virus (LIV) is a tick-borne encephalitis flavivirus transmitted to sheep and other mammals via the bite of an infected tick.

In severe cases, death may occur within three days of symptom onset.  Cases seem confined to Great Britain, primarily in Scotland, Ireland, and Wales.

Diagnosis typically depends on clinical manifestations (symptoms), although diagnosis may be confirmed using various tests, including the haemagglutination inhibition assay. In many cases, confirmations occur postmortem by isolating the virus from a specific bodily organ.

There are no effective treatments available for LIV, though sheep vaccines are available.

Tick Paralysis

This disease is exactly as it sounds — a progressive type of paralysis that starts at the lower part of a sheep’s body and ascends over time. Symptoms usually begin with poor muscle control, limb lameness, and breathing impairment before developing into full-blown paralysis.

Tick paralysis occurs in sheep due to salivary neurotoxins found in different species of ticks, including Dermacentor variabilis (American dog tick) and Dermacentor andersoni (Rocky Mountain wood tick).

Cases occur worldwide. In the United States, most cases happen in and around the Rocky Mountain states and the Pacific Northwest, though it is sometimes found in the American south.

Diagnosis of tick paralysis typically occurs in the presence of a tick on the sheep combined with clinical manifestations. Some ruminants experience rapid deterioration, so severe cases require prompt emergency veterinary care.

Treatment options include the removal of the tick (which may lead to considerable improvement) as well as antitoxin administration and/or antibiotics.

Tick-Borne Fever (Relapsing Fever)

Also known as relapsing fever, tick-borne fever is a bacterial disease transmitted by Ixodes ricinus (sheep tick). Rickettsia, the bacteria responsible for the illness, is often transmitted to mammals via ticks, lice, and fleas. In sheep, symptoms include sudden fever, depression, and weight loss.

Tick-borne fever occurs among sheep primarily in Europe, though there is a form of tick-borne fever in the United States caused by Borrelia hermsii that infects humans.

Diagnosis of tick-borne fever in sheep is usually made using a Polymerase Chain Reaction (PCR) test.

Treatment typically involves the administration of antibiotics, particularly oxytetracycline. This antibiotic has been approved by the FDA for use in sheep.

Babesiosis

Sheep may be infected by several species of Babesia, a type of parasite, but two particular species are more clinically significant concerning sheep.

Babesia motasi causes sheep babesiosis and is transmitted by tick species of the Haemaphysalis genus, including Haemaphysalis punctata, or the red sheep tick. Babesia ovis is transmitted by Rhipicephalus bursa, a multi-host tick.

It’s important to note that B. ovis regularly causes severe illness in sheep, with mortality rates as high as 50 percent.

Babesiosis infections are seen worldwide but are most common in tropical and subtropical regions. Cases are common in the Middle East, southern Europe, and some African and Asian countries.

Diagnosis of babesiosis usually involves light microscopy of blood smears.

Treatment options for sheep babesiosis include Imidocarb or diminazene aceturate. Imidocarb is considered the most effective treatment.

Theileriosis

There are several types of theileriosis parasitic infection among sheep, including:

• T. lestoquardi (transmitted by ticks of the genus Hyalomma)
• T. luwenshuni (transmitted by ticks of the genus Haemaphysalis)
• T. uilenbergi (transmitted by ticks of the genus Haemaphysalis)

In China, theileriosis is highly pathogenic, causing considerable health effects and disease among sheep flocks. T. uilenbergi, in particular, causes significant mortality in sheep. Sheep infected with theileriosis experience a multitude of symptoms, including:

• Persistent fever
• High heart rate
• Cough
• High respiratory rate
• Loss of appetite
• Slow-moving digestion (ruminal hypomotility)
• Enlarged lymph nodes

Most cases of theileriosis among ruminants occur across southern Europe, northern Africa, and various countries in Asia, rarely expanding outside of the tropical and subtropical regions.

Diagnosis involves microscopic observation of blood and lymph smears.

Treatment options include chemotherapeutic drugs, such as parvaquone, buparvaquone, and imidocarb. However, these pharmaceuticals rarely eradicate the parasite. As such, sheep with theileriosis may be treated but maintain a carrier status (meaning they’ll always have the parasite, though internal populations are controlled).