Pox in Sheep and Goat

Pathologic Observations on Sheep and Goat Pox

Mahir A.G. Kubba¹, Yousef M. Abouzeed² and Sayed R. El-attar¹

1Department of Pathology and Clinical Pathology, 2 Department of Microbiology and Parasitology, Faculty of Veterinary Medicine, Al-fateh University. Tripoli-Libya

Abstract Pathological investigation was carried out on pox disease outbreak in a local flock in Tripoli, Libya. Sheep and goats of different ages and sex suffered a short course of illness with mortality rate approximating 35%. Affected animals showed clinical signs of fever, depression and anorexia associated with the characteristic skin lesions and a general enlargement in superficial regional lymph nodes. Skin lesions consisted mainly of raised erythematous macules of 3-5cm which spread all over the body but were more evident in skin regions devoid of wool or hair. Postmortem examination revealed the existence of grayish nodules in the rumen. The lungs were pneumonic and showed multiple variably sized (0.5- 2 cm) well circumscribed grayish rounded patches on the pleura which extend into the parenchyma. The mesenteric and other regional lymph nodes were enlarged. The histopathological examination revealed epidermal cell vacuolation which contained eosinophilic intra-cytoplasmic inclusion bodies. The lymph nodes and the spleen were depleted and the kidneys and the heart revealed interstitial nephritis and myocarditis respectively. The lungs showed proliferative bronchiolo-alveolitis. These pathological changes are highly indicative for pox disease. In this work, we have described and discussed an outbreak of pox disease in a local flock. Reviewing the literature, it was found that this article is the first to document the pathological changes of the disease in Libya.

Key words: Sheep pox, Goat pox, Pathology, Sheep pox cells.

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Address `of correspondent: Dr. Mahir Kubba, Tripoli Libya, P.O box: 13447 e. mail : [email protected]

Introduction

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Pox is a highly contagious viral disease of animals and man. It is caused by a wide range of epitheliotropic double stranded DNA viruses which belong to the family Poxviridae. The disease in sheep and goat is caused by sheep pox virus and goat pox virus respectively, which are closely related members of the capripox genus. ( 1 ). Experimental induction of the disease has also been performed ( 2 ). Sheep pox is prevalent in North Africa, Asia and Southern Europe with a mortality rate ranging from 50% in adults and 100% in lambs ( 3 ). Variation in breed susceptibility was also reported. The virus gain access via the skin or the respiratory system then reaches the systemic circulation through the lymphatic system where it disseminate in the skin and other target organs. In the skin, the virus is thought to inhabit and replicate in the proliferating keratinocytes. Many authors have described developmental sequence of pox lesions which usually occur on wool devoid skin including the cheeks, lips and nostrils as well as the tongue and gum ( 4, 5, 6). The virus-infected keratinocytes undergo vacuolation then rupture forming multi-loculated vesicles. These changes stimulate dermal hyperemia and leukocyte immigration forming macule. The advancement in cellular vacuolation and inflammatory response causes progression of macules into papules, vesicles, pasteules, crust and scar. Inclusion bodies in the epidermal cells and in ‘sheep-pox cells’ which represent sites of viral multiplication are characteristic.

Materials and methods

Autopsy tissue samples of the skin, tongue, lip, rumen, lung, kidney, heart and brain together with skin biopsies were routinely processed for microscopic examination. Specimens were fixed in 10% neutral buffered formalin, dehydrated in increasing concentration of ethyl alcohol, cleared in xylol then embedded in wax. Sections of 5-6 microns were stained with Hematoxyline and Eosin (H&E).

Results

Clinical signs:Affected animals were febrile, depressed, reluctant to move and off feed. There were

mild respiratory signs with catarrhal nasal discharge and mucopurulent conjunctivitis. Erythematous maculae were found on the mammary gland, inner aspects of the thigh, elbow ,perineum, and other wool devoid regions. These maculae were especially pronounced in sheep. Whitish plaques and ulcers were also found on the gums, tongue and inner lips. Mortalities were more pronounced among young animals and death toll approached 35% (14 out of 40).

Postmortem findings:Dead and recumbent animals had peculiar skin lesions which covered the body but

were particularly prominent on the udder, perineum, elbow and other wool devoid regions (Fig.1). These lesions comprised slightly raised ovoid erythematous plagues of 0.5- 3 cm in diameter with or without a depressed dark center. Whitish plaques and ulcers were also found on the gums, tongue and inner lips (Fig.2). The conjunctivae were severely congested and the regional lymph nodes were enlarged. The skin lesions were smaller, shallow and less Eryrthematous in goats.

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Dissection revealed the involvement of the rumen, heart, lung, kidneys and regional lymph nodes. The ruminal mucosa showed multi-focal areas of pale keratinized thickening (Fig.3), while both kidneys and the heart had multiple slightly raised grayish white patches on the surface and in the parenchyma (Fig.4,5). The lungs were mounted with multiple variably sized firm pale nodules. Those which are located directly under the pleura constituted grayish white circular areas which extend into the sub-pleural tissue forming nodules (Fig.6). Both lungs, also, showed alternating areas of atelectasis and emphysema. Mesenteric and other regional lymph nodes were enlarged and edematous.

Microscopic findings:

Sections of the skin showed vacuolar degeneration and necrosis with occasional vacuole formation in the stratum spinosum. Many of the vacuolated cells contain one or more intracytoplasmic, variably eosinophilic usually ovoid inclusion bodies (Fig.7).The dermis was hyperemic and edematous and was infiltrated with acute inflammatory calls. The engorged dermal capillaries were also studded with microthrombi (Fig.8). Similar epithelial and vascular changes were found in the tongue, lips and the ruminal mucosa. The lung showed multi-focal proliferative bronchiolo-alveolitis (Fig. 9). The bronchiolar epithelium showed uneven squamous metaplasia of varying intensities. The alveolar walls were thickened and lined by multiple layers of swollen epithelium which occasionally contained eosinophilic intra-cytoplasmic inclusion bodies. Hyperemia, edema and inflammatory cell infiltration were prominent in the lung. The myocardium showed changes indicative for acute non-suppurative myocarditis .There were focal aggregations of mononuclear cells which induced marked tissue damage (Fig.10). Mononuclear cell aggregations indicative of interstitial nephritis were also noticed in the renal tissue and were associated with tubular nephrosis and tissue damage (Fig.11). The spleen and lymph nodes showed lymphocytic depletion, cortical necrosis and proliferation in histiocytes. . Sheep pox cells, or the so called ‘cellulus claveleulus’ which are a characteristic finding of the disease were also noticed. These cells resemble monocytes, macrophages or fibroblasts and are prevalent in the dermis and inter-alveolar connective tissue in the vicinity of blood vessels. They are vacuolated cells with a peripherally located nuclear chromatin and contain eosinophilic intracytoplasmic inclusion bodies (Fig.12).

Discussion

Sheep and goat pox have long been known as diseases of economic importance in different parts of the world. Apart from America, the United Kingdom and Europe in which the disease has been eradicated ( 7 ), many countries including those of north east Africa still harbor and suffer greatly from its economic impacts. Economic losses result from high mortality rate, decreased milk production and damage to hides and wools as well as limiting trade and preventing the development of livestock production (8). The later, have also added that imported breeds of sheep and goats were found to develop severe disease when they are moved into an endemic areas. The morbidity and mortality rates can approach 100% in newly imported highly susceptible flocks. Libya, is not an exception and the disease in addition to other enzootic diseases, participates effectively in inducing heavy economic losses

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as well. This is most probably due to poor vaccination and sanitation programs, improper insect eradication as well as lack of owner’s commitment.

In the current flock, the clinical signs, postmortem and microscopic findings were consistent with the literatures of concern (4, 5, 6). However, although confirmation of the disease necessitate certain applications for the detection of pox virus particles or its antigens or DNA sequence(PCR), which are not available, many literatures adopt the clinical findings and pathological changes as satisfactory for preliminary diagnosis. (3, 6). The inability of viral identification renders the determination of whether our sheep and goats were infected by sheeppox and goatpox viruses respectively or by a common agent impossible. It was stated that most isolates are host specific, with sheep pox virus mainly causing disease in sheep and goatpox virus predominantly affecting goats ( 9 ). On the other hand, some isolates, can cause serious disease in both species and genetic sequencing demonstrated recombinant strains which usually have intermediate host specificity (10). Local field observations have demonstrated that, in mixed flocks, when goats get infected with the disease, sheep usually contract it, but goats resist the infection when sheep are infected (Personal communications).

Pox disease is not uncommon in Libya and its diagnosis depends essentially on the clinical signs. This, however, does not help in providing an accurate and comprehensive database necessary for determining the precise causative agent, on which a satisfactory vaccination programs are established.

References

1- Kitching R.P. and Taylor W.P. Clinical and antigenic relationship between isolates of sheep and goat pox viruses. Tropical Animal Health and Production (1985). 17, 64-74.

2- Bowden TR, Babiuk SL, Parkyn GR, Copps JS, Boyle DB. Capripoxvirus tissue tropism and shedding: A quantita-tive study in experimentally infected sheep and goats. Virology. 2008;371:380-93.

3- Jones T.C. Hunt R.D. King N.W. Veterinary Pathology(Book), Sixth edition ( 1997). Lippincott, Williams and Wilkins.

4- Martin W.B and Aitkin I.D Diseases of sheep, Fourth edition (2000), Blackwell publications.

5- McGavin M.D and Zachary J.F. Pathologic basis of veterinary disease. Fourth edition (2007), Mosby Publishing.

6- Jubb K.V.F. Kennedy P.C. and Palmer N. Pathology of domestic animals. 5th edition, Vol. 1(2008), Saunders college publishing.

7- Sellers R.F. International importance of some exotic virus infections in sheep. In Diseases of sheep. MartinW.B.(ed.), Blackwell scientific apublications, Oxford.(1983).

8- Yeruham I, Yadin H, Van Ham M, Bumbarov V, Soham A, Perl S. Economic and epidemiologic aspects of an outbreak of sheep pox in a dairy sheep flock. Vet Rec. 2007;160:236-7.

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9- Rao TV, Bandyopadhyay SK. A comprehensive review of goat pox and sheep pox and their diagnosis. Anim Health Res Rev. 2000;1:127-36.

10- Hosamani M, Mondal B, Tembhurne PA, Bandyopadhyay SK, Singh RK, Rasool TJ. Differentiation of sheep pox and goat poxviruses by sequence analysis and PCR-RFLP of P32 gene. Virus Genes. 2004;29:73-80.

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Fig.1: Erythematous flat raised areas in the skin of the udder, perineum and between the thighs. Fig.2: Macules and ulcers on the tongue and inner lips. Fig.3: Multiple keratinized mucosal elevations in the rumen. Fig. 4: Kidney showing, grayish white subcapsular patches of variable sizes.

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Fig. 5: Grayish white patches on the epicardium (black arrow). Fig. 6: Circular whitish patches (red arrow) scattered on the lung which shows areas of emphysema (white arrow) and atelectasis (black arrow). Fig.7: Vacuolated keratinocyted in the stratum spinosum containing eosinophilic

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intracytoplasmic inclusion bodies (black arrow) (x 1000). Fig.8: Microthrombus occluding a small arteriole (black arrow) in the dermis which is infiltrated by inflammatory cells (x 250).

Fig. 9: Proliferative bronchiolo- alveolitis. The bronchiolar epithelium is metaplastic and the alveolar walls are thickened with an increase in alveolar epithelium. The alveoli are filled with inflammatory edema and inflammatory cells. Fig. 10: Acute interstitial nephritis with focal mononuclear cell infiltration between the tubules. The tubules are degenerated and necrosed. Fig.11: Focal myocardiomalacia due to mononuclear cell aggregation. There is an increase in sarcolemmal cells. Fig. 12: Sheep pox cells characterized by

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vacuolated cytoplasm and a peripherally located chromatin and contain eosinophilic intracytoplasmic inclusion bodies ( black arrow)

الخالصةوالماعز األغنام جدري عن مالحظاتمرضية

.¹د. - د كبة الغني عبد .²ماهر - د زيد أبو العطار ¹يوسفمحمد رشاد السيد1- األمراضوالتشخيصالمعملي والطفيليات- 2قسم الدقيقة اإلحياء قسم

األغنام محليمن والتيظهرتفيقطيع حاالتمرضالجدري عن دراسة إجراء تم

. واإلناث الذكور من مختلفة أعمار المرضفي ظهر ولقد فيطرابلسبليبيا والماعز

حواليمن نفوق ألي المرضية% 25أدي التغيرات وبينت وجيزة فترة في القطيع من

الصوف من الخالية تلك وخاصة الجلد علي اإلبعاد مختلفة حمراء بقع وجود الظاهرية

وجود التشريحية الصفة وأظهرت واللثة اللسان علي تقرحات إلي إضافة الشعر أو

القلب الكليوسطح قشرة علي ملساء رمادية الكرشوبقع بطانة علي متفرقة عقد

عليغشاء األبعاد مختلفة رمادية دائرية بقع الرئتين علي ظهر وقد متنهما وفي

تفجيفي المهجرية التغيرات وبينت التهابية تغيرات إلي إضافة المتن الجنبوفي

الميل حامضية ستوبالزمية اشتمالية أجسام علي احتوائها مع للجلد السطحية الخاليا

والغدد الطحال في ليمفاوي نضوب وظهر مة االد في التهابية تغيرات إلي إضافة

. أما والقلب الكلي وبينيفي بؤري ليمفاوي ب التها وجود لوحظ كما الليمفاوية

للخاليا وانتشار شديد احتقان مع حوصلية التهاباتقصيبية لوحظوجود فقد الرئتين

األغنام في لتشخيصمرضالجدري مبدئيا كافية التغيرات هذه وتعتبر االلتهابية

ليبيا في الحيوانات هذه في للجدري المرضية التغيرات الورقة هذه وتوثق والماعز

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