Rinderpest Virus
Introduction
Rinderpest, “cattle plague” in German, is the most devastating livestock disease in history. A virus, it presents quickly and has a high mortality rate. It infects all members of the artiodactyla order (even-toed ungulates). Believed to have originated in Asia, it spread east across Europe, then south through Africa. Out breaks throughout history have claimed millions of cattle and undomesticated ruminants, leading to large-scale famines, economic loss, and ecological disturbances. Finally, after a global vaccination and eradication effort, rinderpest joined small pox as the only viruses to have been driven to extinction by humans.
Classification
Baltimore Classification: Group V
Family: Paramyxoviridae
Genus: Morbillivirus
Brief History
Evidence of rinderpest dates back to as early as 3,000 BCE in Egypt, based on records of its symptoms. It established in Europe by the fourth century with the Hun invasions, and out breaks have been documented throughout the Middle Ages. Fifteen outbreaks were reported in the fourteenth century across the continent. In the eighteenth century it claimed an estimate of more than 200,000,000 domesticated cattle (NY Times 1866).
Rinderpest returned to Africa in the nineteenth century with the Italian cattle imports from Yemen and India to Somalia. The first African epidemic began in 1887, and quickly spread and killed over 90% of the domestic and wild ruminant populations in Ethiopia, Kenya, the Sudan, and Uganda (Tambi et al. 1999). The virus is especially fatal to the zebu cow breeds, which originated in Asia and is now bred extensively in East Africa. Several East African tribes, predominantly the Maasai, rely heavily on their cattle as a source of food, material, money, and status – a vital element of their culture. Rinderpest infects water buffalo, yaks, African buffalo, giraffes, elands, kudus, wildebeest, and Tragelaphine species of antelopes, impacting ecosystems as well as human societies. The virus never established across the Atlantic Ocean, or in Australia.
Characteristics
Rinderpest virus (RPV) has been categorized as a Morbillivirus, a genus of Paramyxoviruses, and is closely related to canine distemper virus and the measles. The virion has a spherical capsid and inner envelope, and a nonsegmented, negative single stranded RNA genome that codes for eight proteins, six structural and two non-structural. These viruses’ surface proteins bind to a host’s cell membrane. The virion then fuse with the host cell, emptying its genetic content and own polymerase. The virus then immediately begins to replicate, and buds off new virions.
The virus moves quickly. It can be transmitted via direct contact, contaminated water, and through short distances in the air. The virion can be easily deactivated by desiccation from heat and sunlight, however the close packing and herding of domestic cattle and the normal behavior of most the affected ruminants to herd aid in the virus’ transmission. The incubation lasts less than three weeks, with symptoms arising as soon as three days after infection. The virus targets the lymphatic system, and the epithelial cells in the respiratory system and gastrointestinal tract (Lund 2000). Early signs include fever, depression, loss of appetite, and soreness along the gums. Nasal and ocular discharge follows, then by necrotic lesions in the mouth and gastrointestinal tract, bloody diarrhea, swollen lymph nodes, and dehydration. An animal is contagious a few days before nasal and ocular discharge appears and all bodily fluids are infectious. During an epidemic, morbidity and mortality is between 80 to 100 percent.
Vaccine and Eradication
Before a vaccine was developed, quarantine and euthanasia were the best solutions for controlling an outbreak. Walter Plowright developed the tissue culture rinderpest vaccine (TCRV), also called the Plowright tissue culture vaccine, in 1962 by growing a live-attenuated strain in calf kidney cells, following Jonas Salk’s methods for the Polio vaccine. The vaccine required 90 or more passages through the cell cultures, but once it was complete, resistance lasted over ten years, sometimes for life. Although the virus has an RNA genome, which typically mutate too quickly for an effective long-term vaccine, the RPV serotype, its surface proteins, has remained the same. This trait means that a vaccine for one RPV strain is effective against them all.
However this vaccine has its drawbacks. The virion’s instability requires refrigeration, making it ineffective for vaccination programs in rural areas. Cattle also sometimes displayed moderate symptoms after inoculation. A recombinant vaccine was later developed using the virus’ surface proteins to generate an immune response. Vaccinia is a typically asymptomatic virus and served as a vector for the small pox vaccine implemented in the pathogen’s eradication. Vaccinia was designed to express RPV haemagglutinin (HA) and fusion (F) surface proteins from the Kabete “O” strain, the most virulent rinderpest strain, to induce protective immunity.
The Pan African Rinderpest Campaign commenced in 1986 with 35 participant countries. The Food and Agriculture Organization of the United Nations launched the Global Rinderpest Eradication Program in 1994 with the goal of a rinderpest free world by 2010. The last known case of rinderpest was in 2001 in Kenya, the last vaccinations were given in 2006, and the virus was declared extinct in the wild October 2010.
