Research and analysis

APHA parasitology group: annual review of literature and horizon scanning report, 2022

Updated 24 January 2024

Ruminant, porcine, avian and miscellaneous species parasitic disease surveillance in Great Britain in 2022

The Veterinary Investigation Diagnosis Analysis database (VIDA) contains a record of every diagnostic submission from livestock and wildlife in Great Britain (England, Scotland and Wales), not including Northern Ireland, made to the Veterinary Investigation Centres of the Animal and Plant Health Agency (APHA), its partner post-mortem examination providers and to Scotland’s Rural College Veterinary Services (SRUC VS). VIDA database represents only submissions of clinical diagnostic material.

Small ruminants

According to the VIDA database, parasitic gastroenteritis (PGE) was the most common disease diagnosed in sheep in 2022 in Great Britain. A total of 1,071 diagnoses of PGE were made in 2022, which includes haemonchosis (190 cases) and nematodirosis (95 cases). Diarrhoea, wasting and death were the main clinical signs associated with the diagnosis of PGE. Most of the diagnoses of PGE were recorded in adults (35.6%) and post-weaned lambs (36.2%). Almost 60% of all diagnoses were reached from carcase submissions. When PGE is suspected, a total estimated worm count, as part of a post-mortem examination, can be a more informative way to estimate worm burden than faecal egg count testing alone.

Historically haemonchosis (Haemonchus contortus infection) was considered only to be a problem in the South of England, but as in 2020 and 2021, the geographic distribution is now more widely across Great Britain. The relatively high number of cases in 2022, compared to previous years, is likely to have been influenced by free testing for this parasite offered by APHA.

Nematodirosis (Nematodirus battus infection) was diagnosed in 8.8% of PGE diagnoses, with 69.5% of these cases in pre and post-weaned lambs; 10.5% in adults; and 19% were of unknown age. Nematodirosis is an important cause of diarrhoea and mortality in young lambs, predominantly in spring.

Under certain climatic conditions disease can occur very quickly, with little or no warning. Cold weather delays hatching, so when there is a sudden change in temperature it can trigger a mass hatch. If this coincides with the time when lambs are starting to eat significant amounts of grass (over about 6 weeks old), the impact can be severe.

In 2022 ovine toxoplasmosis cased 136 cases of ovine abortion. Toxoplasma gondii is a protozoan parasite that can infect pregnant sheep and cause abortion or the birth of weak lambs. These ewes are then protected against further challenge by the development of immunity. An effective vaccine is also available.

Other frequently diagnosed parasitic diseases were coccidiosis (118) and sheep scab (70).

Clinical coccidiosis was the most common cause of diarrhoea diagnosed in pre-weaned lambs. Coccidiosis typically affects young lambs, 3 to 9 weeks of age, resulting in signs of diarrhoea, ill thrift and death. 15 species of Eimeria are recognised in sheep, of which 2 (Eimeria ovinoidalis and Eimeria crandallis) are significant pathogens. Thus, the presence of large numbers of oocysts in sheep is not necessarily indicative of disease and oocyst speciation is necessary to differentiate between highly pathogenic and low pathogenic species.

Control of coccidiosis relies on improving environmental hygiene and the prevention of the exposure of naïve lambs to oocysts. Anticoccidial medications are available for treatment and prevention and the timing of their use is important. More information regarding ovine clinical coccidiosis can be found in the Vet Record Surveillance focus article Coccidiosis in sheep.

Cattle

According to the VIDA database, cryptosporidiosis was the most common parasitic disease (232 cases), followed by coccidiosis (185) and fasciolosis (89), in Great Britain cattle in 2022. The top diagnoses remain the same as in 2021.

PGE can occur in any grazing animal and should be considered for those which are failing to thrive, especially if also diarrhoeic. It is important to bear in mind that faecal worm egg counts are not reliable for identifying significant parasite burdens in cattle and low counts, especially if in liquid faeces, are potentially significant. Examples of this were seen in 2022, when PGE was confirmed by estimated total worm count testing on carcases submitted for post-mortem examination, that did not have high egg count results.

The first diagnoses of parasitic pneumonia (lungworm, husk) were made this year as early as July 2022, through either faecal sampling or post-mortem examination. Reports of lungworm outbreaks in adult cattle have increased over the past 3 decades, particularly in Scotland. The main presenting sign was coughing in animals at pasture. In some submissions, parasitic pneumonia was the sole identified cause of death, but secondary bacterial pneumonia was a feature in some cases.

Pigs

According to the VIDA database, porcine coccidiosis continues to be the most common parasitic disease diagnosed through the Great Britain scanning surveillance network in pigs in 2022. Other parasitic diseases diagnosed were:

• cryptosporidiosis
• helminthiasis
• lungworm
• sarcoptic mange

Cystoisospora suis is typically associated with coccidiosis in pre-weaned piglets while Eimeria species can cause disease in older pigs, in certain epidemiological situations. An item in the pig disease surveillance and emerging threats report for January
to March 2022 and in the May 2022 Veterinary Record surveillance report described a coccidiosis outbreak in replacement breeding pigs with diarrhoea. Coccidiosis is an unusual diagnosis in older post-weaned pigs.

Diagnoses within the Great Britain scanning surveillance network are occasionally made in a well-recognised epidemiological scenario involving young adult replacement breeding pigs, reared in hygienic environments leaving them naïve to Eimeria species, are then moved to ground heavily contaminated with oocysts.

Clinical signs are of diarrhoea, sometimes also with wasting, lethargy and even deaths. Such cases are due to Eimeria species infection. Speciation is recommended when high oocyst counts are encountered in this clinical and epidemiological scenario. Eimeria debliecki is often the main species detected, although a mix of other Eimeria species may also be detected (including E. suis, E. perminuta, E. polita). The exposure to high challenge results in disease usually within 2 weeks and often concurrent with salmonellosis. 

Avian

According to the VIDA database, Coccidiosis caused by Eimeria acervulina in chickens (27 cases) was the most common parasitic disease diagnosed in poultry in 2022, followed by blackhead/histomonosis (17 cases) and helminthosis (17 cases).

Toxoplasma gondii was associated with an unusual presentation of neurological signs in chickens from a smallholder premises, probably caused by ingestion of oocysts from cats, which are the definitive host for the parasite. The consumption of raw or undercooked meat from contaminated birds represents a potential risk of zoonotic infection (APHA 2022).

Miscellaneous, exotic and wildlife species

The top 4 diagnoses in exotic and wildlife species in 2022 were PGE (alpaca, antelope, bison, deer, llama and otter), haemonchosis (alpaca, llama), coccidiosis (alpaca, hare, llama) and fasciolosis (alpaca, deer). In 2022 there were 41 cases of PGE with 28 cases in alpacas, 8 in deer and 2 in llamas. Most of the diagnoses in alpacas were in adults and post-weaned animals showing clinical signs such as wasting, diarrhoea, recumbency or just found dead without prior signs observed.

APHA parasitology surveillance projects

Haemonchus testing in sheep

APHA offered free testing for Haemonchus spp. using the peanut agglutination test between July and October 2022. For the enhanced surveillance, 342 samples from 256 holdings were tested and 81% were positive. This was a significant increase in haemonchosis in 2022 compared to previous years. However, the free testing is likely to have influenced this. Read the full report in the small ruminant disease surveillance and emerging threats report for October to December 2022.

Sheep scab testing in Wales 

Sheep scab was the most common skin disease diagnosed in sheep. Free examination of skin scrape samples from sheep showing clinical signs of sheep scab in Wales was once again funded by the Welsh Government.

The aims of the project were to:

• support accurate diagnosis of pruritic sheep
• promote correct treatment
• achieve successful control of sheep scab

The project ended on 1 April 2022 and a full report of this study was published by APHA. The full report can be viewed in the surveillance report into free sheep scab testing, November 2020 to March 2021.

Tick-borne fever and bovine babesiosis

In 2022, free testing using the dual pan-piroplasm and Anaplasma phagocytophilum PCR was available for suspected cases of bovine babesiosis and tick-borne fever. This helped to inform on-farm control planning and will also help our understanding of disease epidemiology, which is evolving in the face of climate and land use change. A summary of the Bovine Babesiosis project was published in the small ruminant disease surveillance and emerging threats report for July to September 2022 and a paper published by McFazdean et al (2023).

Parasitic gastroenteritis

APHA and Moredun Research Institute are collaborating on a surveillance project named ‘What worms? What wormer resistance risk?’ project, which aims to investigate Ostertagia ostertagi in cattle in England and Wales; and resistance, or reduced efficacy of O. ostertagi to benzimidazoles. Free testing for worm egg counts are available on faeces samples from first season grazing animals. If significant parasitic burdens are identified, effective treatments can be used and the health plan updated.

Exotic worms and worm-like parasites in imported and travelled dogs

APHA and the European Scientific Counsel Companion Animal Parasites (ESCCAP) UK and Ireland launched a project in 2022 to encourage diagnosis and reporting of 3 exotic worms and worm-like parasites in imported and travelled dogs:

• Linguatula serrata
• Dirofilaria repens
• Thelazia callipaeda

There are currently multiple sources of best practice guidance for the prevention, diagnosis and control of these exotic parasites recommended by different stakeholder groups.

• European Society of Dirofilariosis and Angiostrongylosis
• European Scientific Counsel Companion Animal Parasites
• Thelazia callipaeda information note

Exotic parasites should be considered as possible infections in imported pets. Vets and nurses are in the front line of UK biosecurity and must be prepared to give accurate travel advice to clients.

Horizon scanning for new and re-emerging veterinary parasitological threats relevant for Great Britain

Report of fowl cyst mite in England

Laminosioptes cisticola is known colloquially as the fowl cyst mite. The life cycle is poorly understood but the mite is usually found in the subcutaneous tissues, although it has been reported in a range of other tissues. The mite affects poultry and game birds, as well as psittacines and passerines. When the mites die, they become encysted in collagen and small, flat to oval nodules may be seen in the subcutaneous tissues. The mite can therefore affect meat quality. L. cisticola was last reported in Britain in 1977 (Amure and Stuart, 1977) but has re-emerged in in a smallholder flock in Southern England (Grist and others, 2022). The prevalence of this mite in the UK is currently unknown.

Antimicrobial resistance

Suspected lack of antimicrobial efficacy should be reported to the Veterinary Medicines Directorate (VMD) under the Suspected Adverse Reaction Surveillance Scheme.

If you find that an antimicrobial is not working as well as it should, this is known as a “Suspected Lack of Efficacy” situation and you should:

• report the event to the VMD’s Suspected Adverse Reaction Surveillance Scheme (SARSS) team using a ‘yellow’ form (MLA252A) or online via the VMD website
• arrange investigations to determine if this is a resistance problem or a different cause of the lack of efficacy - the manufacturer of the anthelmintic used may be able to help with this investigation

Anthelmintic resistance in ruminants

Anthelmintic resistance (AR) has been identified in worm populations in UK ruminants for decades and there are increasing trends for the presence of AR to many of the commonly used anthelmintics.

Detection and investigation of AR is an important part of APHA’s surveillance activities. The APHA offers routine Macrocylic Lactone (ML), Benzimidazole (BZ) and Levamisole (LEV) anthelmintic resistance testing. During 2022, 5 ML, 3 BZ and no LEV AR were confirmed in post-weaned ruminants.

AR in Haemonchus is common worldwide. However only resistance to Benzimidazoles has been demonstrated in the UK. In addition to Levamisoles and Macrocyclic Lactones, Closantel and Nitroxynil are also effective and provide a narrow spectrum treatment option for Haemonchus.

Experience in Australia has demonstrated that maintaining a susceptible population in-refugia is essential to combating AR and consequently, as with other gastro-intestinal parasites, worming regimes should be designed to take this into consideration. Further guidance from SCOPS is available about Haemonchus contortus.

A case of fasciolosis was detected through the APHA Thin Ewe Project and triclabendazole treatment failure was suspected. A large number of live adult fluke were in the liver at post-mortem examination, despite having received flukicide treatment 4 weeks previously. An alternative adult flukicide, which targeted adults, was recommended.

Useful information regarding the sustainable control of parasites in ruminants are available from the website of these organisations:

• Sustainable Control of Parasites (SCOPS)
• Control of Worms Sustainably (COWS) groups

Scientific and veterinary parasitology papers published in peer review journals by APHA in 2022 (APHA authors in capitals)

1. Beristain-Ruiz, D.M; Garza-Hernandez, J.A; Figueroa-Millan, J.V; Lira-Amaya, J.J; Quezada-Casasola, A; Ordonez-Lopez, S; Laredo-Tiscareno, S.V; Alvarado-Robles, B; Castillo-Luna, O.R; Floriano-Lopez, A; Hernandez-Triana, L.M; Martinez-Ibanez, F; Rivera-Barreno, R; Rodriguez-Alarcon, C.A (2022) Possible association between selected tick-borne pathogen prevalence and Rhipicephalus sanguineus sensu lato infestation in dogs from Juarez city (Chihuahua), northwest Mexico-US border. Pathogens 11 (5) 552.

2. Bianco, C; Fenemore, C; Cafiso, A; Everest, D; Schock, A (2022) Scaly leg due to Knemidokoptes sp. in a bullfinch (Pyrrhula pyrrhula): Common is common but keep an open mind for new findings! Veterinary Record Case Reports 10 (1) e244.

3. Brandell, E.E; Jackson, M.K; Cross, P.C; Piaggio, A.J; Taylor, D.R; Smith, D.W; Boufana, B; Stahler, D.R; Hudson, P.J (2022) Evaluating non-invasive methods for estimating cestode prevalence in a wild carnivore population. PLoS One 17 (11) e0277420.

4. Carson, A; Jones, B; Grove-White, D (2022) Managing liver fluke on hill farms. Veterinary Record 191 (3) 115-117.

5. Gonzalez, M.A; Goiri, F; Prosser, S.W.J; Cavidanes, A; Hernandez-Triana, L.M; Barandika, J.F; Hebert, P.D.N; Garcia-Perez, A.L (2022) Culicoides species community composition and feeding preferences in 2 aquatic ecosystems in northern Spain. Parasites and Vectors 15, Article Number: 199.

6. Hernandez-Triana, L.M; Folly, A.J; Sewgobind, S; Lean, F.Z.X; Ackroyd, S; Nunez, A; Delacour, S; Drago, A; Visentin, P; Mansfield, K.L; Johnson, N (2022) Susceptibility of Aedes albopictus and Culex quinquefasciatus to Japanese encephalitis virus. Parasites and Vectors 15, 210.

7. Johnson, N; Phipps, L.P (2022) Tick-borne diseases of livestock in the UK. In: Nuttall P (ed); Climate, ticks and disease; CABI, Wallingford, 413-417.

8. Johnson, N; Phipps, L.P; Hansford, K.M; Folly, A.J; Fooks, A.R; Medlock, J.M; Mansfield, K.L (2022) One Health approach to tick and tick-borne disease surveillance in the United Kingdom. International Journal of Environmental Research and Public Health 19 (10) 5833. https://doi.org/10.3390/ijerph19105833 0-362.

9. Jones, R.A; Williams, H.W; Mitchell, S; Robertson, S; Macrelli, M (2022) Exploration of factors associated with spatial-temporal veterinary surveillance diagnoses of rumen fluke (Calicophoron daubneyi) infections in ruminants using zero-inflated mixed modelling. Parasitology 149 (2) 253-260.

10. Jones, R.O; Geddes, E; Mohr, S; Bell, I.R; Brulisauer, A.G; Pritchard, C; Nisbet, A.J; Burgess, S.T.G; Busin, V (2022) Spatial and temporal analysis of sheep scab notifications in Scotland, 2014-2019. Veterinary Record 190 (8) e1488.

11. Lawson, B; Robinson, RA; Briscoe, A.G; Cunningham, A.A; Fooks, A.R; Heaver, J.P; Hernandez-Triana, L.M; John, S.K; Johnson, N; Johnston, C; Lean, F.Z.X; Macgregor, S.K; Masters, N.J; McCracken, F; Mcelhinney, L.M; Medlock, J.M; Pearce-Kelly, P; Seilern-Moy, K; Spiro, S; Vaux, A.G; Folly, A.J (2022) Combining host and vector data informs emergence and potential impact of an Usutu virus outbreak in UK wild birds. Scientific Reports 12, Article number: 10298.

12. Macrelli, M; Mackintosh, A (2022) Tongue worm (Linguatula serrata) infection in a dog imported into the United Kingdom from Romania. Veterinary Record Case Reports 10 (2) e281.

13. McFadzean, H; Johnson, N; Phipps, L.P; Hobbs, R.L (2022) High morbidity associated with an outbreak of tick-borne disease in a dairy herd, Cornwall. Veterinary Record Case Reports 9 (4) e171.

14. Medlock, J.M; Hansford, K.M; Gandy, S; Vaux, A.G.C; Keane, E; PHIPPS, P; Johnson, N (2022) Managing red sheep ticks in Sussex (letter). Veterinary Record 190 (5) 202-203.

15. Phipps, L.P; Hansford, K.M; Hernandez-Triana, L.M; Golding, M; McGinley, L; Folly, A.J; Vaux, A.G.C; De Marco, M.F; Carter, D.P; Medlock, J.M; Johnson, N (2022) Detection of Borrelia and Babesia species in Haemaphysalis punctata ticks sampled in Southern England. Ticks and Tick-borne Diseases 13 (2) 101902.

16. Ruiz-Gonzalez, M.X; Kelly, M; Moret, Y; Brown, M.J.H (2022) Parasite resistance and immunity across female castes in a social insect. Behavioural Ecology and Socio-biology 76, Article number: 56.

17. Swinson, V; Jorge, D; Macrelli, M (2022) Monitoring parasite burdens and investigating suspected parasiticide resistance in cattle. Veterinary Record 190 (9) 36

18. Viveros-Santos, V; Hernandez-Triana, L.M; Ibanez-Bernal, S; Ortega-Morales, A.I; Nikolova, N.I; Pairot, P; FOOKS, A.R; Casas-Martinez, M (2022) Integrated approaches for the identification of mosquitoes (Diptera: Culicidae) from the volcanoes of central America physiographic sub province of the state of Chiapas, Mexico. Vector-Borne and Zoonotic Diseases 22 (2) 120-137.

19. Wright, I; Macrelli, M; Diesel, G (2022) Surveillance for exotic worms and worm-like parasites (letter). Veterinary Record 190 (6) 244

Parasitology endemic disease alerts

Date	Subject
22 March 2022	First Nematodirus cases
13 April 2022	Rising temperatures increase risk of early blowfly strike
18 May 2022	Tick borne disease testing (national)
18 May 2022	Tick borne disease testing (Thirsk only)
29 June 2022	Sudden deaths due to haemonchosis
14 October 2022	Parasitic gastroenteritis in growing lambs

Parasitology surveillance publications (non-peer review) by the APHA parasitology team in 2022

1. Parasitology component within the hot weather alert document
2. Taking the sting out of vector borne diseases
3. APHA marks World Mosquito Day
4. Free sheep scab testing in Wales – COEEML Conference
5. Managing liver fluke on hill farms
6. Imported disease summaries for cats and dogs

Report references (alphabetical order)

APHA (2022) Disease Surveillance in England and Wales, March 2022. Veterinary Record, 190; Issue 7, 276-280.

APHA (2022) Disease Surveillance in England and Wales, May 2022. Veterinary Record, 190; Issue 11, 431-476.

Amure, J. and Stuart, J. C. (1977) A case of Laminosioptes cysticola infection. Veterinary Record, 101, 387.

Grist, A; Parsons, D. G; Bianco, C; Cafiso, A. and Foster, A. P. 2022. Suspected Laminosioptes cysticola (fowl cyst mite) lesions in backyard chickens in southern England. Veterinary Record Case Reports, e460.

McFazdean, H; Johnson, N; Phipps, L.P; Swinson, V; Boden, L.A. (2023) Surveillance and Risk Analysis for Bovine Babesiosis in England and Wales to Inform Disease Distribution. Animals 13; 13 p2118.