Jackson Conaty, School of Veterinary Science, University of Sydney; Jarrad Sanderson and Sally Thomson, Department of Agriculture and Water Resources
Lumpy Skin Disease
Lumpy skin disease (LSD) is a vector borne viral disease of cattle that causes relatively low mortality however morbidity associated with the disease can result in animal welfare issues and significant production losses. Infection typically causes an acute disease with fever, depression and characteristic skin nodules. There may also be a marked reduction in milk yield as well as abortion in pregnant animals. Originally limited to Africa, LSD has spread rapidly throughout the Middle East, southeast Europe and Russia in recent years.
The global distribution of LSD is changing and as LSD becomes established in more countries, particularly in Europe, the risk of introduction to Australia increases.
LSD is listed as a notifiable disease by the World Organisation for Animal health (OIE) and is on the Australian national list of notifiable animal diseases. Australia is free of LSD and has never reported a case of the disease.
Aetiology
The LSD virus is a large, enveloped, double-stranded DNA virus of the genus Capripoxvirus and family Poxviridae. Other diseases caused by capripoxvirusesinclude sheep and goat pox. LSD virus is very stable, surviving in an infectious state for months in skin lesions and scabs. Virus can persist in the environment for up to six months and in dried hides for up to 18 days1. Farm environments may therefore remain contaminated for long periods, particularly in the field where cleaning and disinfection is not possible.
LSD virus primarily infects cattle, with Bos taurus breeds being more susceptible to clinical disease than Bos indicus breeds. Asian water buffalo (Bubalis bubalis) are also susceptible to LSD, therefore the disease has the potential to become endemic in northern Australia if it becomes established here.
Distribution
LSD was first described in southern Africa and has since spread northwards through most of sub-Saharan Africa. Since 2012, LSD has become endemic in Turkey and has spread throughout the Middle East (including Israel, Palestine, Jordan and Lebanon), Caucasus (including Azerbaijan, Armenia and Georgia), Kazakhstan, the Southern Russian Federation and the Balkan Peninsula (including Cyprus, Greece, Bulgaria, the Former Yugoslav Republic of Macedonia, Serbia, Montenegro, Albania and Kosovo). Currently there is an increased risk of LSD reaching Central Asia, Western Europe and Central Europe1.
Transmission and spread
Transmission of LSD is primarily associated with mechanical transfer of virus by a range of biting arthropod vectors.2 Other routes (such as direct contact, fomites and contaminated feed sources) are also possible but much less likely. Local and long distance spread of LSD can occur through the movement of infected cattle and vectors. Experimental transmission of LSD has been shown in multiple arthropod species including mosquitos, blood-sucking ticks such as Rhipicephalus appendiculatus and biting flies such as Stomoxys calcitrans2. The presence of vectors will vary between regions, while vector survival and spread are dependent on favourable environmental conditions such as humidity and warm weather3. Transmission through milk and semen is also possible.
Clinical disease
The incubation period of LSD is one to four weeks and disease may be clinical or subclinical. Clinical disease is characterised by fever (>40.5°C), enlarged lymph nodes and prominent skin nodules. The nodules commonly appear on the head, neck, perineum, genitalia, udder and limbs but may occur anywhere on the body. Nodules can vary from one to five centimetres in diameter and, depending on disease severity, may be present in small numbers or completely cover the animal. As the disease progresses, the centre of these nodules ulcerates, resulting in the formation of a scab predisposing the animal to secondary bacterial infections. Pneumonia and mastitis are common complications of the disease. Ulcerative lesions may also develop on the eyes and on oral and nasal mucous membranes. Generalised oedema may be apparent in the limbs, brisket and genitals. Other clinical signs include lachrymation, nasal and ocular discharge, a sharp drop in milk yield and a decrease in body condition score. Abortion, intrauterine infections and temporary or permanent infertility of cows and bulls may occur4. Sub-clinical infections with LSD are common.
Diagnosis
LSD should be suspected when animals present with fever, enlarged lymph nodes and the characteristic skin nodules. LSD is clinically similar to pseudo-lumpy skin disease (bovine alphaherpesvirus 2) therefore samples should be submitted to rule out LSD when clinical signs indicate the disease may be present.
Post-mortem findings may include nodular grey-pink lesions with caseous necrotic cores in the nasopharynx, trachea, bronchi, lungs, gastrointestinal tract, renal cortex and genitalia. Enlarged and haemorrhagic lymph nodes may also be observed.
Laboratory testing is necessary for a definitive diagnosis and samples should be collected early in the development of clinical signs. Samples to collect include:
- serum – from clinically affected, and suspected exposed animals
- EDTA blood (7–10ml per animal) – from live, clinically affected animals
- fresh tissue, in particular skin nodules, scabs, internal lesions and regional lymph nodes
- fixed tissue (in neutral-buffered formalin), in particular scabs, skin nodules, internal lesions and regional lymph nodes
Blood and fresh tissue samples should be chilled and transported at 4°C with frozen gel packs. Formalin fixed samples can be transported at room temperature. Do not freeze samples at -20°C or below as it reduces the sensitivity of virus isolation and molecular diagnostic tests.
Control
In the event of an LSD outbreak, the official response policy of Australia is to eradicate the disease in the shortest possible time using stamping out. Additional control measures would include control of insect vectors, tracing and surveillance, sanitary disposal of carcasses, movement controls and quarantine, decontamination of surfaces and equipment, and public awareness campaigns.
Eradication of LSD is difficult and early detection is essential for successful control and eradication, particularly if vectors become involved. There has been variable success in controlling the disease in south-east Europe where some countries still struggle to contain outbreaks from 2015. In southern Europe vaccination has been used to effectively control LSD outbreaks however in other areas vaccination has not been successful. There is currently no LSD vaccine approved for use in Australia. If wild buffalo populations and cattle in northern Australia’s extensive rangelands were exposed to LSD, reservoirs of the virus could establish. If this were to occur, eradication would be extremely difficult.
Refer to the AUSVETPLAN Lumpy Skin Disease manual for a more comprehensive explanation of Australia’s prevention and response policy.
Keeping Australia LSD Free
Australia maintains its LSD-free status and greatly reduces the risk of incursion through the enforcement of strict biosecurity policies and border controls. Australia’s focus is on ensuring that the level of risk in products that arrive at its borders is already managed to acceptable levels. Stringent, scientifically informed import regulations are in place for cattle skins and hides. The import regulations are supported by rigorous inspection and quarantine protocols at Australia’s national borders.
Risk to Australia of introduction of LSD
Illegal importation of commodities containing or contaminated with LSD virus is the most likely route of entry of LSD into Australia. Arthropod vectors carrying LSD virus may be transported to Australia in commercial containers sent from endemic countries. However the risk of this pathway is low because virus survival on insect vectors is short.
Global distribution of LSD is changing. As LSD becomes established in more countries, the risk of introduction to Australia will increase. Monitoring global spread is important and will allow us to continually revise our prevention strategies to ensure the risk to Australia remains low.
How Australian veterinarians can help
Under Australia’s current quarantine protocols and importation restrictions, the risk of LSD introduction is regarded as low. However it is important that Australian veterinarians maintain current knowledge and remain alert to the possibility of emergency disease incursions as early detection and laboratory confirmation is critical for a rapid and effective response.
Unusual cases of disease, particularly when emergency animal diseases are suspected, should be reported directly to state or territory government veterinarians or through the Emergency Animal Disease Watch Hotline (1800 675 888).
References
1. Tuppurainen, E.S.M., Alexandrov, T. & Beltrán-Alcrudo, D. Lumpy skin disease – A field manual for veterinarians. FAO Animal Production and Health Manual No. 20. Rome. Food and Agriculture Organization of the United Nations (FAO) 2017. doi:10.2903/j.efsa.2015.3986
2. Tuppurainen ESM, Lubinga JC, Stoltsz WH et al. Mechanical transmission of lumpy skin disease virus by Rhipicephalus appendiculatus male ticks. Epidemiology and infection 2013;141:425-430.
3. Tuppurainen, E.S.M., et al. Review: Capripoxvirus Diseases: Current Status and Opportunities for Control. Transboundary and Emerging Diseases 2017;64 (3):729-745. doi:10.1111/tbed.12444.
4. Tuppurainen, E.S.M., et al. Field observations and experiences gained from the implementation of control measures against lumpy skin disease in South-East Europe between 2015 and 2017. Preventive Veterinary Medicine 2018; doi:10.1016/j.prevetmed.2018.12.006.