Until the implementation of the control measures mentioned in a previous activity, the mere mention of rabies was enough to awaken an uncontrollable fear. Not surprisingly since, when symptoms of rabies appear, the disease is almost always fatal. There are other viral infections, also zoonoses, which raise the same alarm in people. We will focus on two paramyxoviruses, Hendra and Nipah viruses, and a filovirus, ebola virus. The viruses that cause them belong to the order Mononegavirales, which we have seen at the beginning of this week. Hendra disease is an emerging zoonosis caused by a paramyxovirus. The first cases were observed on the East Coast of Australia, in Brisbane in 1994. The natural hosts are fruit bats of the genus Pteropus.
The horses are intermediate hosts that possibly get infected with the virus shed by bats with the urine as they fly. Humans acquire the infection when in contact with ill or dead horses. In man, the disease can range from a mild flu-like picture to fatal respiratory or neurological syndromes. Specific antibodies are currently being explored as treatment of the infection. A vaccine for horses is licensed in Australia. Although the disease in humans is uncommon, as of 2013, only 7 cases have been diagnosed, it infuses much fear in the East Coast of Australia. Nipah disease has served as a model for the plot of the film “Contagion”.
The first cases of the disease were observed in Malaysia and Singapore in 1998, when 300 human cases were reported with around 100 deaths. Also, more than one million pigs needed to be sacrificed. The disease produces outbreaks in Bangladesh and Northern India on a yearly basis. Many aspects are similar to Hendra disease. The natural hosts are also Pteropus fruit bats, but humans get infected either from pigs, which act as an intermediary host, from the sap of palm trees contaminated with saliva of bats, or even from other human beings. In humans, the disease can range from asymptomatic to a severe encephalitic syndrome that quickly leads to coma. Many patients also develop a severe respiratory syndrome.
The virus can remain latent and eventually be reactivated. The vaccine against Hendra virus can also cross-protect against Nipah virus. The family of the paramyxoviruses includes many viruses of importance in animals. Some, such as canine distemper, Newcastle disease of birds, peste des petits ruminants or rinderpest, are long-known diseases. The latter disease produced huge devastation in regions where it settled, as the loss of animals meant less supply of animal protein, contributing to famine, and loss of agricultural help. Fortunately, it has been the first animal disease to be eradicated through human efforts. Other diseases, such as distemper of dolphins, seals and other cetaceans, have recently emerged. In humans paramyxoviruses produce well-known diseases, such as measles or mumps.
Both respiratory syncytial virus and parainfluenza virus cause serious respiratory syndromes. Just to mention Ebola is to evoke the most absolute panic. The disease was declared for the first time in 1976 on the banks of the Ebola River in the Democratic Republic of the Congo, formerly known as Zaire. Since then, and from time to time, there are outbreaks in several countries of Equatorial Africa. The disease is caused by a Filovirus of the genus Ebolavirus,
which includes five species: Zaire, Sudan, Taï Forest and Bundibugyo, which are isolated in Africa, and Reston, which has been isolated in the Philippines, but that does not produce disease in humans. Although the natural host is not confirmed, there is much evidence suggesting that it is a zoonosis transmitted by bats. Symptoms include severe bleeding causing weakness and fatigue, vomiting, and diarrhoea. They may appear between 2 to 21 days after being infected, but usually the latency period is 8 to 10 days. Treatment is symptomatic and for now, there is no available vaccine, although it may be close. As you can see, there are many emerging diseases produced by virus similar to the rabies virus.
The bat is thought to be the reservoir for many of them. It is necessary to be always alert to the emergence of new infections and try to control them from the beginning.