(The Gist of Science Reporter) Rare Viral Zoonoses
(The Gist of Science Reporter) Rare Viral Zoonoses
Rare Viral Zoonoses
Zoonoses transmitted between vertebrate animals and humans, have been posing a great challenge worldwide. In, diseases and infections that are naturally
2001, it was estimated that 61% out of the 1415 microbial diseases affecting humans are zoonotic. Among emerging infectious diseases, 75% are zoonotic with wildlife being one of the major sources of infection.
Foot and Mouth Disease (FMD):
FMD, caused by Foot and Mouth Disease Virus (FMDV) of the genus Apthovirus under Picornaviridae family, is a highly contagious disease affecting all cloven-footed animals. Seven serotypes of the virus have been recorded, viz. O, A, C, SAT1, SAT2, SAT3, and Asia1.
The number of human FMD infections is considered insignificant when compared to the devastation they have caused in the animal world. Infections are rare in humans as it crosses the species barrier with difficulty and with little effect, yet it is considered zoonotic due to a few of the documented human cases.
Its incubation period in humans ranges from 2-6 days.
The disease in humans is usually mild and self-limiting. It is manifested in the form of fever, sore throat and development of uncomfortable tingling blisters on the hands, feet and in mouth, including the tongue. Affected individuals usually recover shortly after the last blister formation. Human to human transmission has not been reported yet. Human infection from pasteurized milk has not been reported and the Food Standards Agency considers that the disease has no implications for the human food chain.
Newcastle Disease (ND):
ND is one of the most economically devastating diseases of poultry. Chicken is the most susceptible to infection, with affected flocks experiencing morbidity and mortality rates up to 100%. It is caused by avian paramyxovirus type 1 (APMV-1), member of the genus Avulavirus in the family Paramyxoviridae.
ND has been reported in humans following exposure to large quantities of virus. Laboratory workers and vaccination crews are the most susceptible to infection. Infections in poultry workers are rare and handling or consuming poultry products is not considered a risk factor.
It is manifested as a mild, self-limiting influenza-like disease in humans, with clinical signs of fever, headache, malaise and conjunctivitis. Any form of contact with birds should be avoided at the time of conjunctivitis as the virus is shed for 4-7 days in ocular discharges. Conjunctivitis usually resolves rapidly without treatment. It is suggested that APMV-1 can cause serious opportunistic infections in severely immunosuppressed individuals.
Viruses of zoonotic importance in the genus Orthopoxvirus of family Poxviridae include Buffalopox Virus (BPV), Camelpox Virus (CMLV) and Monkeypox Virus (MPV).
Buffalo Pox Virus (BPV) is the cause of buffalopox, a contagious viral disease, which mostly affects buffaloes but rarely cows and human beings. It was isolated for the first time in 1967 in Northern India and has been continuously reported from the states of Uttar Pradesh, Rajasthan, Andhra Pradesh, Gujarat and Karnataka. Milkers are susceptible to infection and accidental exposure to the virus is accompanied by the development of pox-like local lesions on the hands, forearms and forehead with symptoms of general malaise, fever and axillary lymphadenopathy.
Camelpox is a disease of socioeconomic significance in African and Asian countries with indigenous camel population. Earlier, it was thought that the disease is only confined to camels. However, after the confirmation of the first human cases of camelpox in India, it is now considered a zoonotic disease. Clinical manifestations in humans include eruption of papules, vesicles, ulcers on fingers and hands and finally scabbing.
Two parapoxviruses have been described as zoonotic, i.e. orf virus and pseudocowpox virus. Orf is a disease of sheep and goats, human infections are acquired from affected animals. With an incubation period of 2-4 days, the disease in humans is characterised by the development of macular lesions, papular lesions, and large nodules resembling papillomas, fever, lymphangitis and rarely blindness. The lesions persist for 4-9 weeks, followed by healing without leaving scars.
Pseudocowpox is a disease of cattle that is characterised by the presence of small raised sores and scabs on the teats and udders. Direct contact with infected cows is the predisposing factor for human infections, which leads to the development of painful scabby sores on the hands and arms. The lesion in human is referred to as milker’s nodule.
Vesicular stomatitis is a viral disease of cattle, pigs and horses caused by members of the genus Vesiculovirus under Rhabdoviridae family, producing blister-like sores on the mouth and feet of infected animals. People who are in direct contact with infected animals develop flu-like symptoms and occasional blisters on their hands and in the mouth. According to some authors, conjunctivitis or cheilitis may be observed as an early sign of infection. Acute nausea, vomiting and diarrhoea, in addition to nonspecific flu-like signs have been described in one affected individual. Affected people usually recover within 4-7 days without complications.
Other Zoonotic Viral Infections:
Human B Virus Infection is a serious zoonotic hazard caused by macacine herpesvirus 1/B virus/cercopithecine herpesvirus 1. This infection is common in all macaques used in biomedical research. Usually, this infection is asymptomatic or causes mild disease in animals and is transmitted to susceptible humans through bite, scratch or mucosal contact. The incubation period can be as short as two days to as long as 2-5 weeks. Vesicles, pruritus, and hyperesthesia at the site of bite are often the first clinical sign, followed by ascending paralysis, encephalitis, and death.
Borna disease in horses, sheep, and other domestic mammals is caused by Borna disease virus 1 (BoDV-1) of the family Bornaviridae. Until recently, its status as a zoonotic agent was a matter of debate in the scientific community.
However, a recent study has confirmed that this virus affects humans. Humans can get infected by direct contact with persistently infected animals. The study reported that humans exhibit symptoms of fever, headache and confusion, followed by various neurological signs, deep coma, etc. Some of the patients develop fatal encephalitis when affected by this virus.
Semliki forest virus of the genus Alphavirus of Togaviridae is considered a zoonosis, with predominant signs of headache, fever, myalgia and arthralgia and rare signs of abdominal pain, diarrhoea, and conjunctivitis in affected humans.
Zoonotic diseases are here to stay. Therefore, basic protective and hygienic measures must be taken while handling animals, even if the animals are apparently healthy. Farmers at the field level must also be made aware. Creating awareness about the potential threats would help in striving towards the goal of “One Health” which is going to be future of healthcare in the world after the recent COVID-19 outbreak.