March 30, 2020History of Medicine
Pangolins have not been ruled out yet, as one of the sources of COVID-19. Pangolins have significantly decreased immune responses due to a genetic dysfunction, making them extremely fragile. They are susceptible to diseases such as pneumonia and the development of ulcers in captivity, complications which can lead to an early death. In addition, pangolins rescued from illegal trade often have a higher chance of being infected with parasites such as intestinal worms, further lessening their chance for rehabilitation and reintroduction to the wild.
Pangolins, or scaly anteaters, are mammals of the order Pholidota (from Ancient Greek horny scale). The one extant family, Manidae, has three genera: Manis, Phataginus and Smutsia. Manis comprises the four species found in Asia, while Phataginus and Smutsia each include two species living in Sub-Saharan Africa. These species range in size from 30 to 100 cm (12 to 39 in). A number of extinct pangolin species are also known.
Pangolins have large, protective keratin scales covering their skin; they are the only known mammals with this feature. They live in hollow trees or burrows, depending on the species. Pangolins are nocturnal, and their diet consists of mainly ants and termites, which they capture using their long tongues. They tend to be solitary animals, meeting only to mate and produce a litter of one to three offspring, which are raised for about two years.
Pangolins are threatened by heavy deforestation of their natural habitats and by poaching for their meat and scales, which are used in Chinese traditional medicine for a variety of ailments including excessive nervousness and hysterically crying children, women possessed by devils and ogres, malarial fever, and deafness. Pangolins are also the most trafficked mammals in the world. As of January 2020, of the eight species of pangolin, three (Manis culionensis, M. pentadactyla and M. javanica) are listed as critically endangered, three (Phataginus tricuspis, Manis crassicaudata and Smutsia gigantea) are listed as endangered and two (Phataginus tetradactyla and Smutsia temminckii) are listed as vulnerable on the Red List of Threatened Species of the International Union for Conservation of Nature.
In February 2020, university researchers in China employing genomic sequencing found a 99% match between a coronavirus found in pangolins and SARS-CoV-2, the virus responsible for the 2019-20 coronavirus pandemic. Though a 99% similarity is not necessarily enough to link them, a subsequent whole-genome comparison found that the pangolin and human viruses in fact share only 90.3% of their RNA, thus ruling out the animals as a direct source. The initial speculation about pangolins being the origin of the virus may have led to mass slaughters, similar to what happened to civets during the SARS outbreak.
The name pangolin comes from the Malay word pengguling, meaning one who rolls up. However, the modern name in Standard Malay is tenggiling; whereas in Indonesian it is trenggiling; and in the Philippine languages it is goling, tanggiling, or balintong (with the same meaning).
The etymologies of the three generic names Manis (Linnaeus, 1758), Phataginus (Rafinesque, 1821), and Smutsia (Gray, 1865) are sometimes misunderstood. Carl Linnaeus (1758) invented the Neo-Latin generic name Manis apparently as a feminine singular form of the Latin masculine plural Manes, the Ancient Roman name for a type of spirit, after the animal's strange appearance. Constantine Rafinesque (1821) formed the Neo-Latin generic name Phataginus from the French term phatagin, adopted by Count Buffon (1763) after the reported local name phatagin or phatagen used in the East Indies. The British naturalist John Edward Gray named Smutsia for the South African naturalist Johannes Smuts (1808-1869), the first South African to write a treatise on mammals in 1832 (in which he described the species Manis temminckii).
The order Pholidota in the past was considered to be the sister taxon to Xenarthra (anteaters, sloths, and armadillos), but recent genetic evidence indicates their closest living relatives are the Carnivora with which they form the clade Ferae. Fossil groups like the creodonts and palaeanodonts as even closer relatives to pangolins (the latter group being classified with pangolins in the clade Pholidotamorpha.
The physical appearance of a pangolin is marked by large hardened overlapping plate-like scales, which are soft on newborn pangolins, but harden as the animal matures. They are made of keratin, the same material from which human fingernails and tetrapod claws are made, and are structurally and compositionally very different from the scales of reptiles. The pangolin's scaled body is comparable in appearance to a pinecone. It can curl up into a ball when threatened, with its overlapping scales acting as armor, while it protects its face by tucking it under its tail. The scales are sharp, providing extra defense from predators. Pangolins can emit a noxious-smelling chemical from glands near the anus, similar to the spray of a skunk. They have short legs, with sharp claws which they use for burrowing into ant and termite mounds and for climbing.
The tongues of pangolins are extremely long and like those of the giant anteater and the tube-lipped nectar bat, the root of the tongue is not attached to the hyoid bone, but is in the thorax between the sternum and the trachea. Large pangolins can extend their tongues as much as 40 cm (16 in), with a diameter of only 0.5 cm (0.20 in).
Most pangolins are nocturnal animals which use their well-developed sense of smell to find insects. The long-tailed pangolin is also active by day, while other species of pangolins spend most of the daytime sleeping, curled up into a ball. Arboreal pangolins live in hollow trees, whereas the ground-dwelling species dig tunnels to a depth of 3.5 m (11 ft). Some pangolins walk with their front claws bent under the foot pad, although they use the entire foot pad on their rear limbs. Furthermore, some exhibit a bipedal stance for some behavior and may walk a few steps bipedally. Pangolins are good swimmers and insectivorous. Most of their diet consists of various species of ants and termites and may be supplemented by other insects, especially larvae. They are somewhat particular and tend to consume only one or two species of insects, even when many species are available to them. A pangolin can consume 140 to 200 g (4.9 to 7.1 oz) of insects per day. Pangolins are an important regulator of termite populations in their natural habitats.
Pangolins have very poor vision, so they rely heavily on smell and hearing. Pangolins also lack teeth; therefore they have evolved other physical characteristics to help them eat ants and termites. Their skeletal structure is sturdy, and they have strong front legs that are useful for tearing into termite mounds. They use their powerful front claws to dig into trees, ground, and vegetation to find prey, then proceed to use their long tongues to probe inside the insect tunnels and to retrieve their prey.
Pangolins are solitary and meet only to mate. Males are larger than females, weighing up to 40% more. While the mating season is not defined, they typically mate once each year, usually during the summer or autumn. Rather than the males seeking out the females, males mark their location with urine or feces and the females will find them. If there is competition over a female, the males will use their tails as clubs to fight for the opportunity to mate with her. Gestation periods differ by species, ranging from roughly 70 to 140 days. African pangolin females usually give birth to a single offspring at a time, but the Asiatic species may give birth to from one to three. Weight at birth is 80 to 450 g (2.8 to 15.9 oz) and the average length is 150 mm (5.9 in). At the time of birth, the scales are soft and white. After several days, they harden and darken to resemble those of an adult pangolin. During the vulnerable stage, the mother stays with her offspring in the burrow, nursing it, and wraps her body around it if she senses danger. The young cling to the mother's tail as she moves about, although in burrowing species, they remain in the burrow for the first two to four weeks of life. At one month, they first leave the burrow riding on the mother's back. Weaning takes place around three months of age, at which stage the young begin to eat insects in addition to nursing. At two years of age, the offspring are sexually mature and are abandoned by the mother.
Pangolins are in high demand for Chinese traditional medicine in southern China and Vietnam because their scales are believed to have medicinal properties. Their meat is also considered a delicacy. 100,000 are estimated to be trafficked a year to China and Vietnam, amounting to over one million over the past decade. This makes it the most trafficked animal in the world. This, coupled with deforestation, has led to a large decrease in the numbers of pangolins. Some species, such as Manis pentadactyla have become commercially extinct in certain ranges as a result of overhunting. In November 2010, pangolins were added to the Zoological Society of London's list of evolutionarily distinct and endangered mammals. All eight species of pangolin are assessed as threatened by the IUCN, while three are classified as critically endangered. All pangolin species are currently listed under Appendix I of CITES which prohibits international trade, except when the product is intended for non-commercial purposes and a permit has been granted.
Nucleic acid sequences of viruses taken from pangolins had initially been found to be a 99% match with SARS coronavirus 2 (SARS-CoV-2), the virus which causes COVID-19, and responsible for the 2019-20 coronavirus pandemic. The working theory of researchers in Guangzhou, China, was that SARS-CoV-2 had originated in bats and, prior to infecting humans, was circulating among pangolins. The illicit Chinese trade of pangolins for use in traditional Chinese medicine was suggested as a vector for human transmission. However, pangolins were eventually ruled out as the definitive source of (SARS-CoV-2), namely being the bridge that the virus used to jump from bats to humans, after it emerged that the 99% match did not actually refer to the entire genome, but to a specific site known as the receptor-binding domain (RBD). A whole-genome comparison found that the pangolin and human viruses share only 90.3% of their DNA (at least 99.8% is needed for a conclusive match). Ecologists worried that the early speculation about pangolins being the source may have led to mass slaughters, endangering the animals further, which was similar to what happened to civets during the SARS outbreak.
Many attempts have been made to reproduce pangolins in captivity, but due to their reliance on wide-ranging habitats and very particular diets, these attempts are often unsuccessful. Pangolins have significantly decreased immune responses due to a genetic dysfunction, making them extremely fragile. They are susceptible to diseases such as pneumonia and the development of ulcers in captivity, complications which can lead to an early death. In addition, pangolins rescued from illegal trade often have a higher chance of being infected with parasites such as intestinal worms, further lessening their chance for rehabilitation and reintroduction to the wild. Recently, researchers have been able to improve artificial pangolin habitats to allow for reproduction of pangolins, providing some hope for future reintroduction of these species into their natural habitats.
Taiwan is one of the few conservation grounds for pangolins in the world after the country enacted the 1989 Wildlife Conservation Act. The introduction of Wildlife Rehabilitation Centers in places like Luanshan (Yanping Township) in Taitung and Xiulin townships in Hualien became important communities for protecting pangolins and their habitats and has greatly improved the survival of pangolins. These centers work with local aboriginal tribes and forest police in the National Police Agency to prevent poaching, trafficking, and smuggling of pangolins. These centers have also helped to reveal the causes of death and injury among Taiwan's pangolin population.
Today, Taiwan has the highest population density of pangolins in the world.