The pathology of rinderpest in common warthog, cattle and African cape buffalo experimentally infected with African lineages I and II isolates of rinderpest virus.
The persistence of mild rinderpest in the Eastern Africa region despite continued eradication efforts has been a subject of concern in recent years among the wildlife conservation, livestock production, and scientific communities. The current study has examined the role that wildlife play in the transmission dynamics of the disease, by characterizing the pathology of two recent isolates of rinderpest virus (RPV) in common warthogs (Phacochoerus africanusy; African cape buffaloes (Syncerus caffer) and indigenous cattle (Bas indicusi. Six (6) wild buffaloes, 13 wild warthogs, and 19 indigenous cattle were used in this study involving kudu/Bov/BKN2 and RBKIWP/861l isolates belonging to the African lineages U and I, respectively, ofRPV. Four of the warthogs and four of the cattle were inoculated parenterally with 1043 TCIDso of the African lineage II isolate of RPV. TIle inoculated warthogs were housed in contact with four (4) naive cattle and two (2) naive warthogs. The inoculated cattle were similarly kept in contact with four (4) naive warthogs and two (2) naive cattle. Two other warthogs were inoculated parenterally with a similar dose of the virulent Kabete '0' strain of RPV belonging to the Asian type lineage to serve as positive controls. Another group of fourt 4) cattle was inoculated parenterally with 1048 TCIDso of the African lineage I (RBKIWP/86/l) isolate of RPV and two of these cattle were kept in contact with four naive wild buffaloes and three (3) naive cattle. Two animals of each of the three species were parenterally inoculated with a placebo comprising of minimum essential medium (MEM) devoid of RPV and kept separate as uninfected controls. Cuulc were clinically examined and sampled daily starting from the initial day to the time of necropsy on days 5 to 13, or at convalescence on day 22. Buffaloes and warthogs were chemically immobilized, examined, and sampled on the initial day and then Oil alternate days starting from days 3 to 9 depending on the group. Blood samples were taken in tubes coated with ethylene-diamine tetra-acetic acid (EDT A) lor haematological analysis. The inoculated animals were euthanised for necropsy at the early and late stages of the disease from day 5 to day 13 after inoculation. One each of the uninfccted control cattle and warthogs were also euthanised for necropsy along with the inoculated ones. One sick in-contact warthog was euthanised for necropsy 22 days after being housed with others inoculated with the African lineage" isolate of RPV. Representative tissue samples were obtained from euthanised animals and preserved in 10% neutral buffered formalin. The tissues were then processed, stained with haematoxylin and eosin (I J&E), and examined under the light microscope using the standard procedure. The African lineage 11 isolate of RPV induced a mild disease in the inoculated groups of warthogs and cattle as well as in the warthogs that were kept in contact with the latter. Ilowever, the virus induced a moderately severe disease in the group of warthogs that were kept in contact with inoculated ones. The African lineage I isolate of RVP induced a mild clinical disease in both the inoculated and in-contact cattle as well as in lite illcontact buffaloes. The virulent Kabete "0" strain 011 the other hand induced a severe, rapidly fatal disease in the inoculated warthogs. The disease induced by the various strains was clinically characterized by oculonasal discharges. stomatitis or varying degrees, fever in a few cases, and rarely, diarrhoea. In addition, cyanosis of the skin, vcscicular dermatitis ami inflammation or joints were observed ill warthogs at varying degrees of frequency. Transient leucopaenia was the mC11n haematological change induced by the different isolates while the main gross lesions were congestion of the gastrointestinal mucosa with ulceration in two cases, and congestion of lymph nodes and Peyers' patches. The main histological lesions induced ill warthogs and cattle by the three isolates of RPY were varying degrees of epithelial necrosis mostly affecting the mucosa of the gut and lyrnphocytolysis in lymphoid tissues. These: were occassionally accompanied by formation of syncytia and eosinophilic intracytoplasmic inclusion bodies and often infiltrated with neutrophils and macrophages, These findings showed that warthogs are susceptible to the wildlife-derived African lineage 1I (kudulBovIBKN2) isolate of RPY developing mild to moderately severe disease depending on the mode of transmission. They are capable of transmitting the virus to cattle as well as contracting it from cattle resulting in mild disease. They are also capable of transmitting it to other warthogs resulting in moderately severe disease that may be fatal in a proportion of infected warthogs due to secondary complications. The results from this study rsuggest that wildlife plays an important role in the epidemiology of rinderpest but further research is needed to clarify the dynamics involved in the maintenance and persistence of the disease.