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The enteroviruses are a genus of ssRNA viruses associated with several human and mammalian diseases. Historically the most significant has been the Poliovirus. Other types are coxsackie and echovirus.

Enterovirus are the most common cause of aseptic meningitis and can cause serious disease especially in infants and the immunocompromised.

"Human enteroviruses (family Picornaviridae) infect millions of people worldwide each year, resulting in a wide range of clinical outcomes ranging from unapparent infection to mild respiratory illness (common cold), hand, foot and mouth disease, acute hemorrhagic conjunctivitis, aseptic meningitis, myocarditis, severe neonatal sepsis-like disease, and acute flaccid paralysis. In the United States, enteroviruses are responsible for 30,000 to 50,000 meningitis hospitalizations per year as a result of 30 million to 50 million infections. Serologic studies have distinguished 66 human enterovirus serotypes on the basis of an antibody neutralization test, and additional antigenic variants have been defined within several of the serotypes on the basis of reduced or nonreciprocal cross-neutralization between prototype and variant strains. On the basis of their pathogenesis in humans and experimental animals, the enteroviruses were originally classified into four groups, polioviruses, coxsackie A viruses (CA), coxsackie B viruses (CB), and echoviruses, but it was quickly realized that there were significant overlaps in the biological properties of viruses in the different groups. The more recently isolated enteroviruses have been named with a system of consecutive numbers: EV68, EV69, EV70, and EV71." There "are 62 non-polio enteroviruses that can cause disease in humans: 23 Coxsackie A viruses, 6 Coxsackie B viruses, 28 echoviruses, and 5 other enteroviruses."

"Enteroviruses can be found in the respiratory secretions (e.g., saliva, sputum, or nasal mucus) and stool of an infected person. Other persons may become infected by direct contact with secretions from an infected person or by contact with contaminated surfaces or objects, such as a drinking glass or telephone. Parents, teachers, and child care center workers may also become infected by contamination of the hands with stool from an infected infant or toddler during diaper changes."

Transmission

Poliovirus, as well as coxsackie and echovirus are spread through the fecal-oral route (compare with entero-, of the guts/intestines).

Species and genetics

Enteroviruses are members of the picornavirus family, a large and diverse group of small RNA viruses and "is characterized by a single positive-strand genomic RNA known to have a high mutation rate caused by low-fidelity replication and frequent recombination."

"The enterovirus genus comprises the following species: poliovirus, human enterovirus A (HEV-A) (coxackie A viruses and enterovirus 71), HEV-B (coxsackie B viruses, echoviruses, coxsackie A9 virus, and enteroviruses 69 and 73), HEV-C (coxsackie A viruses), HEV-D (enteroviruses 68 and 70), and at least three animal enterovirus species (bovine, simian, and porcine enteroviruses). They all contain a genome of approximately 7,500 bases and positive [(+)]-strand polarity. After infection of the host cell, the genome is translated in a cap-independent manner into a single polyprotein, which is subsequently processed by virus-encoded proteases into the structural capsid proteins and the nonstructural proteins, which are mainly involved in the replication of the virus"

Poliovirus

Incubation period of poliovirus is 1–2 weeks. The prodromal phase shows: Fever, malaise, myalgia (sore muscles), sore throat, vomiting, and constipation. Poliovirus can affect the spinal cord and cause paralysis. In this case, the disease is referred to as poliomyelitis.

Coxsackie and echovirus

Coxsackie viruses are a non-phylogenetic group. Coxsackie A viruses are mainly associated with human hand, foot and mouth disease. Coxsackie B viruses can cause mild signs and symptoms, similar to a "cold", but these viruses also can lead to more serious diseases, including myocarditis (inflammation of the heart); pericarditis (inflammation of the sac lining the heart); meningitis (inflammation of the membranes that line the brain and spinal cord); and pancreatitis (inflammation of the pancreas).

Echoviruses, on the other hand, are a cause of many of the non-specific viral infections.It is mainly found in the intestine, and can cause nervous disorders.

The usual symptoms of coxackie and echovirus are: Fever, mild rash, mild upper respiratory tract (URT) illness.

Chronic fatigue syndrome

In September 2007, a study published in the Journal of Clinical Pathology reported that acute respiratory or gastrointestinal infections associated with enterovirus may be a factor in chronic fatigue syndrome. The California-based study showed a statistically significant portion of the chronic fatigue study group tested positive for a viral protein compared to the control group.

Enterovirus 71 (EV71)

EV71 was first isolated and characterized from cases of neurological disease in Californiamarker in 1969. "Enterovirus 71 (EV71), the newest member of Enterovirudae, is notable for its etiological role in epidemics of severe neurological diseases in children. It appears to be emerging as an important virulent neurotropic enterovirus in the upcoming era of poliomyelitis eradication". The illness usually peaks in June or July.

"Enterovirus 71 (EV71) infection may be asymptomatic or may cause diarrhea, rashes, and hand, foot and mouth disease (HFMD). However, EV71 also has the potential to cause severe neurological disease. To date, little is known about the molecular mechanisms of host response to EV71 infection. [...] EV71 infection led to increases in the level of mRNAs encoding chemokines, proteins involved in protein degradation, complement proteins, and proapoptotis proteins."

"Enterovirus 71 (EV71), one of the major causative agents for hand, foot and mouth disease (HFMD), is sometimes associated with severe central nervous system diseases. In 1997, in Malaysia and Japan, and in 1998 in Taiwan, there were HFMD epidemics involving sudden deaths among young children, and EV71 was isolated from the HFMD patients, including the fatal cases. The nucleotide sequences of each EV71 isolate were determined and compared by phylogenetical analysis. EV71 strains from previously reported epidemics belonged to genotype A-1, while those from recent epidemics could be divided into two genotypes, A-2 and B."

Treatment

There is no vaccine or antiviral agent known to be effective in treating or preventing EV71 infection. Experimental vaccines and antiviral agents are being worked on. For example, "both bovine and human lactoferrins were found to be potent inhibitors of EV71 infection" and "ribavirin could be a potential anti-EV71 drug.". Enterovirus-induced myocarditis has been successfully treated with interferon-α.

Malaysia and Singapore

In Malaysiamarker, EV71 outbreaks occurred in 1997 and 2000, mainly associated with genotypes B3 and B4. Since 1997, EV71 epidemics (genotypes B and C) have been reported annually in Singapore, with genotype B4 forming the predominant causative agent of a large outbreak in 2000.

Korea

In Korea, an EV71 epidemic in 2000 was caused by a relatively new genotype, C3, which has only rarely been identified outside of Korea in recent years.

Taiwan

A large outbreak of HFMD due to EV71 infection occurred in Taiwanmarker in 1998, including 129,106 case reports, 405 children with severe complications, and more than 80 deaths. After 1998, smaller EV71 epidemics occurred almost annually in Taiwan, primarily associated with EV71 viruses of genotypes C2 and B4.

"Two outbreaks of hand-foot-and-mouth disease (HFMD) occurred in Taiwan between 1998 and 2000.Enteroviruses were isolated from a total of 1,892 patients in this laboratory during this period. Of the virus isolates, enterovirus 71 (EV71) was diagnosed in 44.4% of the patients (132 of 297) in 1998, 2% (13 of 646) in 1999, and 20.5% (195 of 949) in 2000. Genetic analyses of the 5�-untranslated and VP1 regions of EV71 isolatesby reverse transcription-PCR and sequencing were performed to understand the diversity of EV71 in these outbreaks of HFMD. Most EV71 isolates from the 1998 epidemic belonged to genotype C, while only one-tenth of the isolates were genotype B. Interestingly, all EV71 isolates tested from 1999 to 2000 belonged to genotype B. This study indicated that two genogroups of EV71 capable of inducing severe clinical illness have been circulating in Taiwan. Furthermore, the predominant EV71 genotypes responsible for each of the two major HFMD outbreaks within the 3-year period in Taiwan were different."

In 2008, Taiwanmarker's Department of Health (DOH) reported 14 fatalities by enterovirus 71 (EV71), with the September 21 death of an 8-month-old boy.

Hong Kong

In Hong Kongmarker, sporadic EV71 infections with incidences of monoplegia were reported in 1987, and a fatal case was documented in 2001.

The number of EV71 cases in Hong Kong in 2004, 2005, 2006 and 2007 were 35, 8, 16 and 12 respectively. In 2008 , the Centre for Health Protection confirmed the total number of infections to 94 so far. In three of the cases, the children infected had traveled to Guangdongmarker and Fujianmarker.

China

From 1999 to 2004, there were no epidemics of hand, foot, and mouth disease in Shenzhenmarker, People's Republic of Chinamarker, but each year there were small, local outbreaks associated with only a few cases of neurological disease and no reported fatalities. Genetic analysis revealed 19 cases of EV71 among 147 children who had hand, foot, and mouth disease in Shenzhenmarker during this time.

Until 2008, no large EV71 epidemic had been reported on the Chinese mainland, but sporadic infections were common in the southeast coastal area as well as inland regions, such as Beijing, Chongqing, and Jinan. From 1998 to 2004, the only EV71 viruses identified on mainland China belonged to the genotype C4, indicating far less variety in China than in Taiwanmarker.

On May 3 2008, Chinese health authorities reported a major outbreak of EV71 enterovirus in Fuyang city (Anhui province, Chinese: 阜阳) and other localities in Anhui, Zhejiang, and Guangdong provinces. As of May 3 2008, 3736 cases occurring mainly in children have been reported, with 22 dead and 42 critically ill. Some 415 new cases have been reported in the last 24 hours in Fuyang City alone. As of May 5, 2008, 6,300 were sickened by the viral outbreak which killed another child, in Zhejiangmarker raising the death toll to 26 children, with 1,198 other children affected in that province alone. Specifically, an additional 5,151 cases were reported in Anhuimarker province with scores more in 4 other provinces. 8,531 cases of children infected with hand-foot-mouth disease (HFMD) were reported in China. All the children infected are aged below 6, with most of them being under 2. As of May 7 contagious HFMD led to 28 deaths. Xinhuamarker reported the number of people infected, also rose by 4000 to 15,799. The death toll rose by two to 30, on Thursday, while the number of reported cases jumped to 19,962. It was up by 4 to 34 on Friday, and 43 as of May 16, while reported infections jumped to 24,932.

In Jian'oumarker city of Fujianmarker province from October 1 to 17, 2008, Xinhuamarker reported 3 children, all less than 1 year old died, and 110 others became ill due to the toddler's virus, or the hand, foot and mouth disease. In Anhuimarker, the southern Chinamarker virus killed 42 people in April and May, and 27,500 toddlers cases were reported. The outbreaks had been linked with enterovirus 71 (EV71), and there is no vaccine for the disease.

See also

Other serious illnesses that can arise from these viruses:

External links



Sources and notes


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