- Open Access
Pathological studies on postvaccinal reactions of Rift Valley fever in goats
© Kamal; licensee BioMed Central Ltd. 2009
Received: 23 April 2009
Accepted: 06 July 2009
Published: 06 July 2009
RVF live attenuated vaccine (Smithburn strain) was evaluated by using goats as experimental animal. The results indicate that this vaccine cause severe deleterious pathological changes in liver especially in kids and causing abortion in pregnant does. The virus was seen to be propagated inside hepatic cells forming intranuclear inclusions which was also seen by E.M. Viral antigens were detected in hepatic cells, gall bladder, endothelial lining of blood vessels, leukocytes, kidneys and heart by using immunoflourescent technique. It could be concluded that the use of live attenuated vaccine of RVF (Smithburn strain) for immunization of live stock is not safe in Egypt as it considered an endemic area.
Rift Valley Fever (RVF) is a febrile disease that affected livestock and humans, transmitted by mosquitoes and caused by a virus (genus: Phlebovirus, family: Bunyaviridae) that can persist in nature . The virus was first isolated in Kenya in 1930 . Until 1977, Rift Valley Fever disease was geographically limited to Africa, and then it was recorded for the first time in Egypt as an epizootic . The Rift Valley Fever virus is a single stranded RNA with three segments (S, M, and L), each segment is enclosed in a separate nucleocapsid within the virion .
Rift Valley Fever (RVF) virus causes abortion in pregnant animals and a high mortality in young ones and humans especially those suffering other diseases . The most prominent and pathognomonic lesions of RVF virus infection were found in the liver . RVF virus is a hepatotropic virus in vivo and can cause liver necrosis and death in animals . The intranuclear inclusion bodies inside the hepatic cells and the necrotic foci are of diagnostic importance which characterizes RVF infection . The Aim of this Work was to: Evaluate the live attenuated RVF vaccine which was produced locally in Egypt from pathological point of view with discussing the picture of the disease that might result from this vaccine by using young kids, adult does and pregnant does.
Materials and methods
The number of animals used in this study was fourteen (14). They were classified into three groups. The first group was five kids (1.5 month old), the second group was five non pregnant adult does (1 year old) and the third group was four pregnant does (1.5 year old and of three months pregnancy). Meanwhile, the animals were tested serologically against RVF virus to prove that they were completely free from infection and did not contain neutralizing antibodies against RVF virus. Four kids, four non pregnant does and three pregnant does were vaccinated by RVF attenuated vaccine subcutaneously 1 ml/animal.
1-Whole blood. 2-Serum samples. 3-Frozen tissues specimens. 4-Formalin fixed tissues specimens. 5-Glutaraldehyde fixed tissues specimens. 6-Frozen tissues specimens for A.G.P.T.
Erythrocytic count (RBCs) was performed using improved neubauer haemocytometer and hayme's solution. The packed cell volume (PCV) was done using the microhaematocrit centrifuge. Total leucocytic count (TLC) was performed using improved neubauer hemocytometer and turkey's solution. Blood films were prepared and stained using Giemsa stain for differential leucocytic count, which was done by Battelement method. All hematological studies were done according to . While haemoglobin (Hb) was determined using test kits of Diamond according to . Whole Blood Clotting Time was done after ; protocols require standardization of blood volume, clean glass tubes of a standard size and a water bath (25–37°C). Using whole blood immediately after collection; contact activation of coagulation is initiated by the glass tube.
The detection of viral antigen was done by indirect immunofluroscent technique on frozen sections and paraffin sections using hyperimmunserum of RVF which prepared in rabbit and anti-rabbit IgG conjugate with fluorescein isothiocyanate according to, and also by agar gel precipitating test (AGPT) on organ homogenates according to .
Formalin fixed specimens were prepared and examined microscopically . Another paraffin sections were stained by PAS procedure (Periodic acid-Schiff) and Phloxine-Tartarzine stain according to .
5-Transmission electron microscopy examination
The glutaraldehyde fixed tissues specimens were prepared and examined microscopically by the electron microscope .
The RBCs count, Hb concentration and PCV% showed a significant decrease than control in all vaccinated animals beginning from second day postvaccination in group 1&2 and started at 3rd day P.V. in group three. Then showed a significant decrease at 3rd, 4th, 5th, 6th and 7th days P.V. in all vaccinated goats than control. The type of anaemia was detected after determination of MCV and MCHC. The results indicated that the type of anaemia was normocytic normochromic at the 2nd, 3rd and 4th days P.V. in groups (1&2) and at 3rd and 4th days P.V. in group (3). Then the anaemia type became macrocytic hypochromic at 5th, 6th and 7th days P.V. in all groups.
Total leucocytic count (TLC) and differential leucocytic count; there was a significant increase in TLC in 1st, 2nd and 3rd day P.V. in group (1) and group (2) and up to 4th day P.V. in group (3) than control. Significant decrease in TLC was recorded at 6th and 7th days P.V. in group (2). Significant decrease in TLC was recorded at 2nd, 3rd and 4th weeks P.V. in vaccinated animals of all groups. There was a significant increase in segmented neutrophil at 1st, 2nd and 3rd days P.V. in group (1) and group (2) followed by a significant decrease at 6th,7th days P.V. and at and 2nd,3rd and 4th weeks P.V. in both groups. In group (3) a significant increase in segmented neutrophil was recorded at 1st, 2nd, 3rd and 4th days P.V. then a significant decrease in segmented neutrophil was recorded at 7th day P.V. and at 2nd, 3rd and 4th weeks P.V. There was a significant increase in lymphocyte in group (1) at 1st day P.V. and at 1st and 2nd day P.V. in group (2) and at 1st, 2nd and 6th day P.V. in group (3) followed by significant decrease at 2nd, 3rd and 4th weeks P.V. in groups (1) and (2) but at 3rd and 4th weeks P.V. in group (3).
2-The biochemical results
a-Whole blood clotting time(WBCT)
There was a significant prolongation of the whole blood clotting time than control in all vaccinated animals with differences according to the age and physiological states (pregnant or not). The highest level of clotting time was observed in the pregnant does (7.2 minutes) at 7th day P.V. Then gradually decreased in 2nd, 3rd and 4th weeks P.V.
a- AST and ALT in young kids showed an increase beginning from 2nd day postvaccination (P.V.) and reach its peak at 7th day P.V. & 6th day P.V. respectively and was still high at 2nd, 3rd & 4th weeks P.V. than control. b- ALP in young kids showed an increase beginning from 1st day P.V. and reaches its peak at 6th day P.V. and still was high at 2nd, 3rd and 4th weeks P.V. than control.
a- AST and ALT in adult doe showed an increase beginning from 2nd day postvaccination respectively and reach its peak at 5th day and 6th day postvaccination respectively and was still high at 2nd, 3rd and 4th weeks P.V., b- ALP in adult doe showed increase beginning from 1st day P.V. and reaches its peak at 5th day P.V. and was still high at 2nd, 3rd and 4th weeks P.V.
a- AST and ALT in pregnant does showed increase beginning from 2nd day postvaccination and reach its peak at 6th day and 5th day P.V. respectively and was still high at 2nd, 3rd and 4th weeks P.V., b- ALP in pregnant does showed increase beginning from 1st day P.V. and reaches its peak at 6th day P.V. and was still high at 2nd, 3rd and 4th weeks P.V.
4- Histopatholoical Results
Group (1) Kids
Group (2) Adults non pregnant
Group (3) Pregnant Does
4-Results of electron microscopic studies
4-Immunofluorescent microscopic results
5-Agar gel precipitation test (AGPT)
The detection of RVF virus antigen in organs of vaccinated goats with the live attenuated RVF vaccine by agar gel precipitation test (AGPT) on organ homogenates (liver, spleen, kidneys, brain, myocardium and lymph nodes) had given positive reaction in groups 1 and 2 at 1st, 2nd and 3rd days and 4th weeks P.V. and in group 3 (pregnant does) at abortion and parturition either from does or dead or stillbirth foeti.
Kids: Gave positive results from fourth day postvaccination and reached its highest level at 15th day P.V. (0.782) and persist at a high level till the end of the experiment (4 weeks P.V.).
Adult does: Gave positive results from third day postvaccination and reached its highest level at 20th day P.V. (1.006) and persist at a high level till the end of the experiment (4 weeks P.V.).
Adult pregnant does: Gave positive results from 3rd day P.V. and and reached its highest level at 20th day P.V. (0.820) and persist at a high level till the end of the experiment (55 days P.V.).
In the present work we tested the live attenuated RVF vaccine (Smithburn strain) in kids, adult and pregnant goats to investigate the adverse effects induced by the vaccine.
Abortions and parturition of dead foeti were additional signs in group three and occurred after sudden and sharp rise in body temperature (41°C). The abortion takes place in two pregnant does out of three. The 1st one was aborted after 10 days postvaccination and the other pregnant one was aborted after 28 days postvaccination. In this concern,  mentioned that during the epidemic of Rift Valley Fever that broke out in Egypt in 1977, abortions occurred at any stage of pregnancy after a sharp rise of body temperature accompanied by bloodstained nasal discharge.  Mentioned that the inoculation of RVF virus in pregnant ewes resulted in four abortions after 4–12 days with retained placenta.
The results suggested that the causes of abortions and parturition of dead foeti were primarily the direct effect of RVF virus on the genital organs of the pregnant does by causing necrotic changes in the uteri and secondary due to death of the foeti resulted from the infection of the foeti by the RVF virus and propagation of the virus inside the liver of the foeti (RVF antigens in the livers of the aborted and dead foeti were detected by immunoflurescent technique).
The clinical pathological result revealed normocytic normochromic anaemia.  Reported that RVF infection in sheep resulted in a significant decrease in RBCs at 1 to 7 days postinfection.  Found that the experimental infection of RVF virus in sheep, caused fall of RBCs during the course of the disease.
However, from histopathological point the anaemia was haemorrhagic and this was indicated by widespread haemorrhages in most organs (liver, kidneys, epicardium, endocardium and brain). This haemorrhage may be attributed to three reasons; vascular damage which confirmed by viral antigen in endothelium lining of blood vessels by immunofluorescing staining or; consumption of clotting factors which indicated by massive hepatic necrosis of all vaccinated animals or; thrombocytopenia which may be occurred due to adherence of thrombocytes on damaged endothelium blood vessels and this was proved by extramedullary haematopoiesis in which megakaryocytes observed in hepatic sinusoids, lymph nodes and splenic sinusoids .
The clinical results also revealed a significant increase in TLC in the 1st three days in all vaccinated groups and this was resulted from neutrophilia and lymphocytosis and such finding could be attributed to the ability of vaccine to evoke the immune response of animals by stimulation and activation of bone marrow for neutrophilia and lymph nodes for lymphocytosis and this was confirmed histologically by follicular and paracortical hyperplasia of lymph nodes.
On the other hand, decrease in TLC was observed by 2nd week P.V. and this leucopenia was resulted either from neutropenia due to bone marrow affection or from lymphopenia which may be resulted from lymphocytic depletion of lymph nodes and spleen. Our results were concomitant with  who mentioned that leucopenia and lymphopenia resulted in case of RVF virus infection while leucocytosis and lymphocytosis resulted from vaccination. Similar findings were observed by  and .
The results revealed prolongation of the blood clotting time in all vaccinated animals and the highest level of delayed clotting time was observed in the pregnant does (7.2 minutes) at 7th day postvaccination. Our findings were in agreement with  who mentioned that one of the main functions that have been deteriorated by RVF virus infection was the coagulation factors of the blood as demonstrated from the significant prolongation of the clotting time.  Reported that clotting factors produced by the hepatocytes include fibrinogen, prothrombin and other factors. Consequently, decreased functional hepatic mass may result in a diminishing of clotting factor activity in proportion to the degree of hepatocellular damage, leading to prolonged coagulation times and possible bleeding tendencies. Loss of greater than 70 to 80% of the functional hepatic mass is considered sufficient to cause a clinical coagulopathy.
The results also revealed that there were increases in levels of AST, ALT and ALP in all vaccinated animals. This may resulted from hepatic damage and this was in agreement with  who stated that natural infection of RVF virus in sheep caused a significant increase in level of AST and ALT due to liver necrosis caused by RVF virus.
Liver was the most affected organ in all vaccinated groups. The lesions were more obvious and severe in kids than adults. This was in accordance with  who stated that the hepatic necrosis in older animals was slightly less extensive than young kids. There were different types of necrosis, periacinar, midzonal, paracentral or even massive necrosis (pan-necrosis) of most hepatocytes. The necrosis could be attributed to either cytotoxic effect of virus or ischemia that resulted from hepatic haemorrhages due to the damage of the endothelial lining of hepatic sinusoids. However,  mentioned that the frequent paracentral location of the liver lesions is suggesting the association of the changes with anoxia. This finding was in agreement with  who mentioned that in livers of lambs infected with Rift Valley Fever virus naturally, showed scattered grayish-white foci of 1–2 mm in diameter and hemorrhages of varying sizes were seen throughout.
Intranuclear inclusion bodies were detected inside the cells of liver and kidneys of all the vaccinated kids, adults and pregnant does. These inclusions were differed in shape and in some cells the chromatin of the affected nuclei were marginated and disintegrated as shown by the electron microscope examination. The intranuclear inclusions were eosinophilic by Phloxine-Tartrazine stain and surrounded by a hallo and founded inside cells which suffering degeneration and necrosis and located inside or near the necrotic areas in the hepatocytes and the epithelial lining of the renal tubules. Our findings were in agreement with . However,  mentioned that viruses of Bunyaviridae family encode their structural proteins but moreover Phlepoviruses also encode a nonstructural protein (NSs) in the viral RNA (vRNA) of their S segment. For RVF virus, the NSs proteins were reported to be phosphorylated and to accumulate in the nuclei of the infected cells. Studies concerning genomic replication indicated that continous proteins synthesis was required for replication of the RVF viral genome and these proteins were of viral origin. For the viruses in the family Bunyaviridae the structural protein, nucleocapsid protein (N), would function to regulate replication and would be tempered by the presence of nonstructural proteins (NSs), where they exist.
Recently,  mentioned that a better understanding of the factors that govern RVFV virulence and pathogenicity is required, given the urgent need for antiviral therapies and safe vaccines. NSs with anti-IFN activity accumulated in the nucleus. IFN synthesis is regulated by specific transcription factors, including interferon regulatory factor (IRN-3), NF-kappaB, and AP-1. In the presence of NSs, IRF-3 was still activated and moved to the nucleus. So, these results suggest that NSs, unlike other viral IFN antagonists, does not inhibit IFN-specific transcription factors but blocks IFN gene expression at a subsequent step.
The Councilman's-like bodies were seen inside the cytoplasm of swollen, degenerated and necrotic hepatocytes in all vaccinated animals and in the aborted foeti and dead foeti as well. The bodies appeared as intracytoplasmic eosinophilic masses surrounded by hallo zone.
However, in this concern  gave description to the Councilman's bodies as small, hyalinous, round or oval eosinophilic inclusions in the cytoplasm of hepatic cells infected with Yellow fever virus and suggested that these bodies represent necrosis around viral particles. He added that these bodies might also see in other form of toxic or viral hepatitis.  Mentioned that the affected liver cells with RVF virus were swollen, eosinophilic, hyaline cytoplasm, and pyknotic or fragmented nuclei, their appearance suggesting the Councilman's bodies of yellow fever.
Recently,  stated that Councilman's-like bodies were seen in some viral infections and may be due to condensation of cytoplasmic organelles and squestrated from remaining cytoplasm by membranes that fuse with lysosomes (autolysosomes) and may also be derived from other hepatocytes that suffered from apoptosis (apoptotic bodies) and engulfed by remaining hepatocytes.
In the present work, we observed large numbers of apoptotic cells in liver of vaccinated animals by RVF live attenuated vaccine. Our findings are in concurrence with  who mentioned that viral infection can induce PCD in various host target cells. Also we agree with  who mentioned that RVF virus increases the apoptotic hepatic cells. These findings are in concurrence with  who mentioned that Bunyamwera virus nonstructural protein (NSs) counteracts interferon regulatory factor 3 (IRF-3), so leads to the induction of early cell death (PCD).
Russell's bodies were seen inside the necrotic foci in the form of intracellular and extracellular spherical strongly eosinophilic bodies in some cases of group-1 (kids). However,  described the so called Russell's bodies as small, spherical hyaline bodies in cancerous and simple inflammatory growth and in degenerating plasma cells. Then,  discussed the various theories of Russell's bodies origin. The possibilities included, origin from the lymphocytes, origin in plasma cells with later degeneration, origin from mitochondria of cells, and even an origin from a red blood cell swallowed up by a plasma cell. These bodies were seen within the tissue cells (intracellular) and outside the cells (extracellular). The size of Russell's bodies ranged from barely visible up to "half again" as large as red blood corpuscles. The largest round forms were easily seen microscopically. Recently,  mentioned that Russell bodies (RB) are dilated ER cisternae containing condensed immunoglobulins (Ig). As to their biogenesis, it was shown that the synthesis of a mutated Ig, which is neither secreted nor degraded, is sufficient to induce RB formation in cells of different species and histotype. Many disease-linked cases of intralumenal protein accumulation have been described including thyrocytes of congenital goiter patients and hepatocytes of individuals carrying mutated α1 anti-trypsin alleles (PiZ). The correlation between liver disease and PiZ lumenal depositions indicates that the latter can be harmful for cells, but the exact mechanisms that lead to toxicity are not known.
Electron microscopic examination revealed ultrastructure changes in liver and kidneys and viral particles inside hepatocytes cytoplasm. The hepatic cells of vaccinated goats with live attenuated RVF vaccine showed cell with indentation of the nuclear membrane, margination and disintegration of the chromatin. The mitochondria were swollen. Some hepatocytes reveals condensed chromatin on the borders of the nuclei and others revealed more chromatin inside the nuclei. In kidneys the proximal convoluted tubules epithelial cells showed necrotic and fragmented brush borders with signs of necrosis and lyses in their nuclei and other organelles. The distal convoluted tubules showed necrotic microvilli with necrotic and destructed nuclei and lyses of other cell organelles.
Our findings agree with  who mentioned that in liver of newborn lamb infected with RVF virus showed ultrastructural changes. Hepatocytes were primarily affected, while inflammatory and structural changes were secondary.  Mentioned that the characteristic lesions of RVF were in the liver. Margination of the chromatin in a beaded form or its accumulation in clumps on the nuclear membranes was also observed. In this study we detected the RVF virus antigen in tissues by using the immunoflourescent technique (IFAT) and by agar gel precipitation test (AGPT). The IFAT gave strong positive reactions in organs of all vaccinated animals especially in the liver. The hepatocytes, especially those adjacent to the necrotic foci and to the bile ducts and adjacent to the blood vessels were the most affected and gave the strong fluorescent stain. It was a surprise to found that antigen of RVF virus was seen inside the cytoplasm of the epithelial cells of the bile ducts, nearly in all the examined specimens. These findings suggesting that the RVF virus affects the bile ducts in strong manner and propagates inside its epithelium. However,  mentioned that the RVF viral antigen was studied by immunohistochemistry in the liver and was most prominent in the liver and detected in the cytoplasm of hepatocytes which were sparsely scattered throughout the lobules.  Mentioned that RVF virus antigen was detected by immunohistochemical analysis in the liver, where positive staining was localized in coalescing foci of hepatocellular necrosis.
From this point of view, RVF virus (Smithburn's strain) could be dessiminated from the vaccinated animals as a result of its propagation and circulation in the blood of the vaccinated animals and resulted in spreading of the RVF virus in the adjacent environment and infected other susceptible animals and even man. These side effects became more dangerous especially in endemic areas as mentioned by  who found that genetic exchange occurred between strains from different lineages of RVF virus and this hypothesis emphasizes the risk of generating uncontrolled chimeric viruses by using the live attenuated vaccines in areas of endemicity.
It could be concluded that the use of live attenuated vaccine of RVF (Smithburn strain) for immunization of live stock in Egypt is danger. As the use of live attenuated vaccine of RVF (Smithburn strain) could result in the spreading of RVF virus instead of its eradication. In the present work, the results indicate that this vaccine cause severe deleterious changes in various organs and propagated inside hepatic cells in a manner similar to the infection by the virulent RVF virus. So, the use of live attenuated vaccine (Smithburn's strain) for control RVF virus is not advisable in Egypt as it considered an endemic area for RVF virus.
- Linthicum KJ, Davies FG, Kairo A: Rift Valley Fever virus (family Bunyaviridae, genus Phlebovirus). Isolation from Diptera collected during an inter-epizootic period in Kenya. Journal of Hygiene 1985,95(1):197-209.PubMed CentralView ArticlePubMedGoogle Scholar
- Daubney R, Hudson JR, Graham PC: RVF or Enzootic hepatitis. An undescribed virus disease of sheep, cattle and man from East Africa. J Path Bact 1931, 34: 545-579. 10.1002/path.1700340418View ArticleGoogle Scholar
- Darwish MAA, Imam ZE, Omar F, Hoogstraal M: A seroepidemiological survey in man and domestic animals in Egypt. J Egyp Pub Health Ass 1977, 3: 156-163.Google Scholar
- Calisher C: Classification and nomenclature of viruses, fifth Ed. Report of the International Committee on Taxonomy of viruses. Arch Virol 1991, (suppl 2):273-283.Google Scholar
- Meegan JM, Khalil GM, Hoogstrall H, Adham FK: Experimental transmission and field isolation studies implicating Culex pipens as a vector of RVF in Egypt. Am J Trop Med Hyg 1980,29(6):1405-1410.PubMedGoogle Scholar
- Smith HA, Jones JC, Hunt RD: Veterinary Pathology. In Text Book. 2nd edition. Lea & Febiger, Philadelphia, USA; 1972.Google Scholar
- Schmaljohn CS: Fundamental Virology. 3rd edition. B.N. Fields and lippincott. Raven publishers. Philadelphia, USA; 1996.Google Scholar
- Coatzer JAW, Ishak KG: Sequential development of the liver lesions in new born lambs infected with RVF virus. Onderstepoort J Vet Res 1982,49(2):103-108.Google Scholar
- Schalm OW, Jain NC, Carroll EJ: Veterinary Hematology. 3rd edition. Lea & Febiger, Philadelphia, USA; 1975.Google Scholar
- Wintrobe MM: Colorimetric Determination of Haemoglobin. 1 st ed. Clinical Chemistry 1965, 5: 719.Google Scholar
- Lee RI, White PD: A clinical study of coagulation time of blood. Amer J Med Sc 1913, 145: 495.View ArticleGoogle Scholar
- Rej R, Horder M: Aspartate aminotransferase and Alanine aminotransferase activities. In Methods Of Enzymatic Analysis. Volume 3. 3rd edition. Edited by: Bergmeyer HU, Grassl M. Weinheim, Verlag-Chem; 1983:416-433. 444–456Google Scholar
- King PR, King EG: Calorimetric determination of alkaline phosphatase activity. J Clin Path 1954, 7: 322. 10.1136/jcp.7.4.322PubMed CentralView ArticlePubMedGoogle Scholar
- Payment P, Trudal M: Methods and Techniques in Virology. In Text Book. Marcel Dekker, Inc. New York, USA; 1993.Google Scholar
- Mansi W: Slide gel diffusion precipitin. Nature (London) 1958, 181: 1289-1290. 10.1038/1811289b0View ArticleGoogle Scholar
- Lillie RD, Fullmer HM: Histopathology Technique And Practical Histochemistry. 4th edition. McGrew Hill Book Company, NY., USA; 1976.Google Scholar
- Hayat MA: Basic Technics for Transmission Electron Microscopy. Academic Press Inc., Orlando, Florida; 1986.Google Scholar
- Abdel-Ghaffar S, Ayoub NNK, El-Nimr M, Nafeh EK, Malik SK: Rift Valley Fever in Egypt. Bull. De L'Office International des Epizootices 1980, 92: 7-8.Google Scholar
- Wasel MS, Ateia M, Mohsen A, El-Sayed M, Zaki K: Effect of RVF virus on pregnant local Barki ewes after artificial infection. Vet Bull 1990,60(1):21-22.Google Scholar
- Shehta MM: Investigation of blood changes in Rift Valley Fever in Egypt. MV Sc Thesis (Microbiology) College Vet Med Cairo Univ 1982.Google Scholar
- Olaleye OD, Tomori O, Fajimi JL, Schmitz H: Experimental infection of three Nigerian breeds of sheep with the Zinga strain of the Rift Valley Fever virus. Rev Elev Med Vet Pays Trop 1996,49(1):6-16.PubMedGoogle Scholar
- Jubb KVF, Kennedy PG, Palmer N: Pathology Of Domestic Animals. 2nd edition. Academic Press Orlando Florida; 1994.Google Scholar
- Embert HC: Leucocytes: Veterinary Clinical Pathology. 2nd edition. London, Academic Press; 1974:55-81.Google Scholar
- Mouaz MA, Gihan KM, Khirat AM, Aida ED, Khodeir MH: Evaluation of immune response in Egyptian Balady sheep vaccinated with attenuated RVF and PBR vaccines. Assiut Vet Med J 1998,38(76):329-341.Google Scholar
- Agag AEM: Morphopathological and Clinicopathological studies on goats following experimental infection with the RVF virus. MVSc Thesis, Microbiology, Fac Vet Med Cairo University 1983.Google Scholar
- Prater MR: Acquired Coagulopathy II;Liver Disease. In Chalm's Veterinary Hematology. 4th edition. Lippincott Williams & Wilkins, USA; 2000.Google Scholar
- Abou-Zaid AA, Nakashly SA, Nasr MY, Mokhabatly A: Studies on RVF in sheep. J Egypt Vet Med Associ 1995,55(1):339-350.Google Scholar
- Hubbard KA, Baskerville A, Stephanson JR: Ability of a mutagenized virus variant to protect young lambs from RVF. Amer J Vet Res 1991,52(1):50-55.PubMedGoogle Scholar
- Jones TC, Hunt RD, King NW: Veterinary Pathology. In Text Book, Library of Congress. 6th edition. Williams and Wilkins Baltimore, Maryland, USA; 1997.Google Scholar
- Coatzer JAW: The pathology of Rift Valley Fever 1. Lesions occurring in natural cases in new-born lambs. Onderstepoort Journal of Veterinary Research 1977, 44: 205-212.Google Scholar
- Billecocq A, Spiegel M, Vialat P, Kohl A, Weber F, Bouloy M, Haller O: NSs Protein of Rift Valley Fever Virus Blocks Interferon Production by Inhibiting Host Gene Transcription. J Virol 2004,78(18):9798-806. 10.1128/JVI.78.18.9798-9806.2004PubMed CentralView ArticlePubMedGoogle Scholar
- Councilman WT: Diseases and Its Causes. 1st edition. H Holt & Co. New York; 1913.Google Scholar
- Caillet FP, Perros M, Brandenburger A: Programmed killing of human cells by means of an inducible clone of parvoviral genes encoding nonstructural proteins. Embo J 1990, 9: 2989-2995.Google Scholar
- Kohl A, Reginald FC, Freidemann W, Anne B, Richard ER, Richard ME: Bunyamwera Virus Nonstructural Protein NSs Counteracts Interferon Regulatory Factor 3-Mediated Induction of Early Cell Death. Journal of Virology 2003,77(14):7999-8008. 10.1128/JVI.77.14.7999-8008.2003PubMed CentralView ArticlePubMedGoogle Scholar
- Russel W: An address on a characteristic organism of cancer. British Medical Journal, London 1890, 2: 1356-1360. 10.1136/bmj.2.1563.1356View ArticleGoogle Scholar
- Schleicher EM: Giant Russell's bodies in neoplastic cells in a case of leukemic lymphosarcomatosis. Minnesota Medicine 1965, 48: 1125-1130.PubMedGoogle Scholar
- Kopito RR, Sitia R: Aggresomes and Russell bodies, symptoms of cellular indigestion. EMBO Reports 2000,1(3):225-231. 10.1093/embo-reports/kvd052PubMed CentralView ArticlePubMedGoogle Scholar
- Coatzer JAW, Ishak KG, Calvert RC: Sequential development of the liver lesions in new born lambs infected with RVF virus. II. Ultrastructural findings. Onderstepoort J of Vet Res 1982, 49: 109-122.Google Scholar
- Mahmoud AZ, Youssef MS, Ibrahim MK: Pathological Studies on Some Liver Affection In Camel: II-Viral Hepatitis. Egypt J Comp Path Clin Path 1989,2(2):27-32.Google Scholar
- Lugt JJ, Coatzer JAW, Smith MME: Distribution of viral antigen in tissues of newborn lambs infected with RVF virus. Onderstepoort journal of Veterinary Research 1996,63(4):341-347.PubMedGoogle Scholar
- Rippy MK, Topper MJ, Mebus CA, Morril JC: RVF virus-induced encephalomyelitis and hepatitis in calves. Veterinary Pathology 1992,29(6):495-502.View ArticlePubMedGoogle Scholar
- Sall AA, Zanotto PM, Sene OK, Zeller HG, Digoutte JP, Thiongane Y: Genetic reassortment of Rift Valley Fever virus in nature. J Virol 1999, 73: 8196-2000.PubMed CentralPubMedGoogle Scholar
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