Blue Tongue Disease and the Sting Knot

Tiny Midge Bites: Sweden Lacks Funding to Track Disease-Spreading Insects

Sweden is facing a critical gap in itS surveillance of biting midges,or “svidknott,” small insects capable of transmitting serious animal diseases. Despite the growing threat posed by climate change and the northward spread of infections like epizootic hemorrhagic disease and Schmallenberg virus, the country lacks dedicated state funding to monitor these vectors.

The biting midge,measuring just a few millimeters,doesn’t have a distinct suction like mosquitoes. Instead, it bites and feeds from the wound. “They use their saliva to prevent the blood from coagulating and thus spreading the virus through the saliva to the animals,” explains Tobias Lilja, a researcher at Sweden’s National Veterinary Institute (SVA). Viruses like blue tongue are not hardy enough to survive in the habitat and require direct transmission into a new host animal’s blood.

While some EU countries actively survey biting midges, Sweden’s last complete data collection occurred between 2008 and 2010. This older data is still used in EU-level compilations. “We had surveillance of sting in Sweden at the Blue Tongue outbreak in 2008,” says Lilja. However, Erika Chenis, a state veterinarian at SVA, confirms, “We have no state funding today to pay for surveillance.”

This lack of ongoing monitoring means Sweden is potentially unaware of shifts in the biting midge’s active period or its population dynamics. “The active period of the svidkotten may have changed somewhat since our latest monitoring. It may start a week earlier and maybe lasts another week.But we do not know that,” Chenis states.

The implications are significant as climate change facilitates the spread of vector-borne diseases. Epizootic hemorrhagic disease, similar to blue tongue, is currently found in southern Europe and could pose a future risk to Sweden. The Schmallenberg virus, also spread by biting midges, was detected in Swedish sheep and cattle early in 2023.

“It would have been fascinating to monitor the presence of sting knots to be able to make modeling at the detailed level when, where and how the burning knot is affected by the environment, climate and weather factors,” Chenis adds.

Currently, research into biting midges in Sweden is only possible through research funding. A collaborative project between SVA and the Swedish University of Agricultural Sciences (SLU) is investigating the extent to wich biting midges can survive in animal stables during winter. Using UV light traps in selected southern Swedish stables, researchers aim to collect the insects. “We will use UV light that attracts these flying burning knots and then we have a fan that blows them into a catch can. At the bottom of the jar we have ethanol that causes the burning knot to die,” Lilja explains.This two-year project hopes to provide valuable insights for both researchers and animal owners on how to best protect livestock from diseases transmitted by these tiny, yet impactful, insects. However, the broader need for national surveillance remains unaddressed due to funding limitations.

What role do *Culicoides* midges play in the transmission of Blue Tongue Disease?

Blue Tongue Disease and the Sting Knot: A Comprehensive Guide

Understanding Blue Tongue disease (BTD)

Blue Tongue Disease (BTD) is a viral disease primarily affecting sheep, goats, and cattle. While not directly transmissible to humans, it poses a significant economic threat to livestock industries globally. The disease is characterized by cyanosis (blueness) of the tongue, swelling of the face and jaw, and fever. Though,the clinical signs can vary considerably depending on the viral strain and the species affected.

Causative Agent: Orbivirus, a genus within the Reoviridae family. There are multiple serotypes, contributing to the complexity of BTD.

Transmission: Primarily through the bite of Culicoides midges – tiny biting insects. Direct contact with infected animals, contaminated feed, or water can also contribute to spread, though to a lesser extent. Vertical transmission (from mother to offspring) is also possible.

Geographic Distribution: Historically confined to Africa, Asia, and Southern Europe, BTD is increasingly spreading due to climate change and global trade. Recent outbreaks have been reported in areas previously considered free, including parts of Europe and the Americas.

The Sting Knot: A Key Indicator in BTD Diagnosis

The “sting knot” – a localized swelling at the site of a Culicoides midge bite – is often one of the earliest visible signs of Blue Tongue Disease. It’s crucial for early detection and differential diagnosis.

Identifying the Sting Knot

The sting knot typically appears as:

1. Small, raised bump: Initially, it resembles a typical insect bite.
2. Localized swelling: The area around the bite becomes noticeably swollen, often on the ears, muzzle, or around the eyes.
3. redness and inflammation: The skin around the knot will be red and inflamed.
4. Potential for ulceration: In some cases, the knot may ulcerate, leading to secondary bacterial infections.

It’s important to note that not all Culicoides bites result in a sting knot,and the presence of a knot doesn’t automatically confirm BTD. However, it raises suspicion and warrants further examination. Distinguishing it from other insect bites is key; BTD-related knots tend to be more persistent and accompanied by systemic signs.

Clinical Signs of Blue Tongue Disease – Beyond the Sting Knot

while the sting knot is an early indicator,BTD progresses to more severe symptoms. Recognizing these is vital for prompt veterinary intervention.

Fever: Often the first noticeable sign, reaching up to 40-42°C (104-107.6°F).

Swelling: Significant swelling of the face, tongue, lips, and ears. The tongue may become enlarged and protrude from the mouth.

Cyanosis: The characteristic “blue tongue” – a bluish discoloration of the tongue – occurs due to oxygen deprivation.

Salivation: Excessive drooling due to difficulty swallowing.

Lameness: Swelling and inflammation of the coronary band (the area where the hoof meets the leg) can cause lameness.

Ulceration: Ulcers may develop on the mouth, nose, and feet.

mortality: Mortality rates vary depending on the viral strain and the species affected. some strains are highly virulent, causing significant losses in livestock.

Diagnosis and Differential Diagnosis

Accurate diagnosis is crucial for effective BTD management.

Diagnostic Methods

Clinical Signs: Initial assessment based on observed symptoms.

Virus Isolation: Detecting the virus in blood or tissue samples.

PCR (Polymerase Chain Reaction): A highly sensitive and specific method for detecting viral RNA.

Serology: Detecting antibodies against the virus in blood samples. This indicates past or present infection.

Differential Diagnosis

Several other diseases can mimic BTD. It’s essential to rule these out:

Orf (Contagious Ecthyma): A viral disease causing sores around the mouth and nostrils.

Foot and Mouth Disease (FMD): A highly contagious viral disease affecting cloven-hoofed animals. FMD is a reportable disease and must be promptly reported to authorities.

Mucosal Disease (Bovine Viral Diarrhea): A viral disease affecting cattle.

Photosensitization: A condition causing skin sensitivity to sunlight,leading to inflammation and ulceration.

Prevention and Control Strategies

managing BTD requires a multi-faceted approach.

Vaccination: Vaccines are available for some BTD serotypes,providing protection against specific strains. Vaccination programs are crucial in endemic areas.

Vector Control: Reducing Culicoides midge populations through insecticide spraying, habitat modification (reducing breeding sites), and the use of midge traps.

biosecurity: Strict biosecurity measures to prevent the introduction of the virus into susceptible populations. This includes quarantine of imported animals and control of animal movements.

Early Detection and Reporting: Prompt reporting of suspected cases to veterinary authorities is essential for rapid response and containment.

* Livestock Management: Providing adequate