The Civet, the Pangolin and Coronaviruses
Little known mammals to Americans and Europeans before the epidemic of SARS-1 and the pandemic of SARS-2
When the pandemic of Covid-19, a severe acute respiratory syndrome (SARS), started in the Chinese province of Wuhan in 2019, it was rapidly found to be propagated by a new coronavirus, the seventh human variety, and the second to cause a SARS. Thus, the virus was designated SARS-CoV-2. Actually, it was the third severe respiratory disease caused by a coronavirus newly transmitted from animal to humans, if one considers Middle Eastern Respiratory Syndrome (MERS), another new human coronavirus-mediated disease. (see later)
The first SARS struck in multiple municipalities in Guangdong Province in southern China in late 2002 and was found to be caused by the virus SARS-CoV-1. By 2003, it had been identified in Vietnam and a few cases were identified internationally as a result of travel from China to the U.S., Canada, and a small number of other countries. It was a limited but very impactful illness, affecting approximately 8000 persons with a nearly 10 percent death rate. The epidemic subsided and only a rare case has occurred since 2003. The reason for its limited spread and the cessation of the outbreak has not been explained, precisely.
The horseshoe bat is considered the ancestral reservoir for coronaviruses. The SARS-CoV-1 virus is thought to have reached humans through an intermediary host, the masked palm civet. The masked palm civet is a nocturnal mammal native to the Himalayan mountains, India and Southeast Asia; forests being its principal habitat. It is a predator and omnivorous and is capable of spraying a noxious substance from it anal gland in the face of threats, as does the skunk. (Figure 1) It is a very popular food meat in Vietnam and China. Hunting this civet for meat and habitat erosion are its main threats. The evidence for a species of bat being the primary (ancestral) host for coronaviruses and several other viruses is strong. The evidence for the civet as in intermediary was provided in studies of the first SARS outbreak in Guangdong Province in 2002-3.
Early cases were in persons that lived within walking distance of a “wet” food market where live animals were sold, killed, and butchered on site. Food handlers (chefs and other food workers) had a higher prevalence of antibodies to the virus than did those in the community in other lines of work. The presence of antibodies to the virus was found in 13% of persons trading in live animals and in 1% of others in the population. The frequency of antibodies to the causative virus was 73% in those persons who traded principally in masked palm civets. Studies of civets on farms did not find evidence of it being a widespread intermediary host. However, studies of the viral genome in two affected patients (a waitress and a customer), who had both been in the same restaurant that served civet meat, confirmed that the palm civets at that restaurant, at which caged, live palm civets awaiting slaughter were also close to employees and customers, were the intermediary host for the zoonotic transmission.
The second severe respiratory distress syndrome, covid-19, caused by SARS-CoV-2, which occurred in 2019 in Wuhan China was initially an outbreak; it became an epidemic because of the high level of contagion of the virus and the absence of any prior immunity to it, and, subsequently, because of the extent of world travel, it became a pandemic. Like the first SARS regional epidemic, it was thought to be a zoonosis, an infectious disease transmitted by interspecies spread from animals to humans. The Huanan Seafood Wholesale Market in Wuhan, a “wet” food market, was thought to be the location for the interspecies jump of the SARS-CoV- 2 2 virus to humans. Wet food markets in China sell all types of seafood, all sorts of meat (e.g. pork, goat, crocodile, salamander, raccoon dog, civet, many others), poultry (chicken, turkey, geese, peacock, pheasant) and have live products slaughtered on site to ensure freshness. Animal blood, body fluids, feces and raw meat are widely present. The conditions are conducive to animal to human spread of an infectious agent since there are usually no sanitary precautions. It, also, is possible that illicit wild products are sold surreptitiously.
The suspicion about the Huanan Seafood Wholesale Market being the location of transmission of SARS-CoV-2 to humans was based on the very large fraction of early cases in Wuhan that had visited the Market. A nearby Chinese laboratory in Wuhan was studying bat viruses and some have raised questions about mismanagement of security and the release of SARS-CoV-2, inadvertently, from that location. The United States government has made illusions about germ warfare, but experts have determined that the virus was natural and not manufactured. Therefore, this, new, naturally occurring virus could not have been in the Chinese laboratory, as it had never been isolated before. Moreover, it was the most devastating, initially, to the Chinese, so any charge of intentionality seems irrational. Unfortunately, the government of the People’s Republic of China did not act responsibly, initially, failing to advise the World Health Organization of the early outbreak, although several of its physicians tried to do so and its scientists published the sequence of the RNA genome of the virus just weeks after the outbreak making it possible to develop a diagnostic test for the virus, quickly, in any country in the world.
Those countries that recognized the risk of the rapid spread of a new respiratory virus, shown to result in a severe and potentially lethal infection, and which applied well-established epidemiological and infectious disease principles rapidly, such as personal protective steps (e.g. masks, distancing, handwashing) and aggressive testing, tracing and isolating, resulted in their having a significantly lower case incidence, hospitalization rate, and death rate (e.g. Taiwan, South Korea). The United States was not one of those countries, as is painfully evident to most observers. The United States government made two profound mistakes: dismantling our previously established early response mechanisms to emerging infectious diseases and displaying an uninformed, indeed lackadaisical, response to the pandemic.
The intermediate host for onset of covid-19 in the Wuhan market was suspected to have been either pigs, civets or pangolins. The market did not have pangolin on its inventory of products, but there are heavy penalties for the trafficking in this endangered mammal, so it would be trafficked surreptitiously. There is stealth trafficking in pangolin meat and scales in Vietnam and China, notably. The Wuhan market is huge with many vendors: a setting very hard to supervise. The pangolin is an endangered small mammal that is highly prized for its scales and meat in China and other countries in Southeast Asia. Its meat is considered a delicacy and its serving a status symbol. Its scales are used to prepare a type of Chinese traditional medicine and its illicit trade in China is thought to have been a possible source for introducing SARS-CoV-2 into the human population. Chinese scientists have compared the RNA of the new coronavirus, SARS- CoV-2, in human cases with civets, pigs, and pangolin in the region and have found gross similarities, but not a close enough match to indicate any of those three animals were intermediate hosts. It requires a virtual perfect identity to make such a claim. The closest identity they have found was with the coronavirus isolated from a horseshoe bat. Thus far, evidence for a specific intermediary host for SARS-CoV-2 mediating between bat and human has not been found.
One of the unintended effects of the pandemic has been to introduce the pangolin to the world. The pangolin is a nocturnal, toothless animal and is harmless to humans. They have large, protective keratin scales covering their skin; they are the only mammal with this feature. (Figure 2) They live in hollow trees or burrows, depending on the species. Pangolins are nocturnal, and their diet consists, principally, of ants and termites, which they capture using an elongated tongue. They rarely congregate, meeting primarily to mate. Pangolins are threatened by poaching because their meat brings premium prices as a food delicacy, especially in China and Vietnam. Their scales which are made of keratin, as are our finger and toe nails, are inert and have no medicinal value. Nevertheless, they are a highly prized ingredient in some types of Chinese traditional medicine. For these reasons, they are the most trafficked mammal in the world and are an endangered species as a result. Their population size also is reduced by heavy deforestation of their natural habitats. As of January 2020, of the eight species of pangolin, three are listed as critically endangered, three are listed as endangered and two are listed as vulnerable on the Red List of Threatened Species of the International Union for Conservation of Nature.
Many new infectious diseases introduced into the human population in the last 75 years have been thought to be the interspecies spread of various infectious agents from animals to humans. It has been estimated that between 60 and 70 percent of new human infectious diseases are a zoonosis. In 2012, 10 years after SARS-CoV-1 appeared and 7 years before SARS-CoV-2 emerged, another highly pathogenic human coronavirus, Middle East respiratory syndrome coronavirus (MERS-CoV) was identified in the Kingdom of Saudi Arabia and, subsequently, in other countries in the Middle East and North Africa. MERS-CoV continues to cause outbreaks and has resulted in a total of approximately 2500 confirmed cases in 27 countries of which approximately 35% have been fatal by November 2019. The camel has been shown, convincingly, to be the intermediary host in the case of MERS. Often, it takes a long time for these agents to be identified. For example, the disease “acquired human immunodeficiency syndrome” (AIDS) arose from the transmission of the simian immunodeficiency virus from chimpanzees to humans as a result of hunting. Hunters were exposed to the body fluids and ingested meat at least since the 1920’s in the then Belgian Congo. The simian virus moved from two smaller species of monkeys, killed for food by chimpanzees, and then from chimpanzees to humans. The disease entered worldwide consciousness in the 1980’s when its immunological impairment and the patient’s susceptibility to opportunistic infections was highlighted by two physicians in California.
Many experts have urged the United States government to invest more in the identification, analysis, and management of zoonotic threats to its citizens. In considering national security, the responsibility of government should broaden from the largely military and paramilitary (e.g. terrorism and manipulation using the media) focus in considering threats to our citizens and to our way of life to include the risk of epidemic infectious diseases, especially through interspecies spread. In addition, the intentional release of infectious organisms from national laboratories links the zoonoses to bioterrorism.
Figure 1. The masked palm civet. A mammal trafficked for its meat in Asia.
Figure 2. A pangolin. A highly endangered mammal trafficked for its meat and scales in Asia.
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Written July 2020