Arboviruses Picornaviruses And Rabies Virus Notes

Arboviruses Picornaviruses and Rabies Virus

Arboviruses

Arboviruses (arthropod-borne viruses) are diverse group of RNA viruses that are transmitted by bloodsucking arthropods (insect vectors) from one vertebrate host to another.

Transmission cycle: Arboviruses are zoonotic, maintained in the nature between animals and their insect vectors.

• Humans are the accidental hosts and do not play any role in the maintenance or transmission cycle of the virus, except for urban yellow fever and dengue.
• Arboviruses found in India: Over 40 arboviruses have been detected in India:
  • Common: Dengue, chikungunya, and Japanese B encephalitis viruses
  • Rare: Kyasanur-Forest disease, West Nile, Sindbis, Crimean Congo hemorrhagic fever,
  • Ganjam, Vellore, Chandipura, Bhanja, Umbre, Sathuperi, Chittoor, Minnal,
  • Venkatapuram, Dhori, Kaisodi and sandfly fever viruses.

Read And Learn More: Micro Biology And Immunology Notes

Chikungunya

Chikungunya fever is a re-emerging disease characterized by fever with arthralgia.

• Chikungunya Human Transmission: Aedes mosquito, primarily Aedes aegypti which bites during day time, rarely by vertical transmission from mother to fetus, blood transfusion
• Chikungunya Clinical Manifestations:
• Incubation period is about 5 days (3–7 days)
• Most common symptoms are fever and severe joint pain (due to arthritis)
• Chikungunya Arthritis is polyarticular (migratory), affecting the small joints.

Chikungunya Epidemiology:

• India: Reported during 1963–1973; e.g. Kolkata in 1963 and South India in 1964. Since then, it was clinically quiescent in world between 1973–2005.
• Re-emergence (Reunion Outbreak): In 2005, Chikungunya re-emerged in Reunion
  Island of Indian Ocean and then spread to India and other countries.
• India (at present): Chikungunya is endemic in several states.
• States: Karnataka, Tamil Nadu, Andhra Pradesh and West Bengal have reported higher number of cases.
  • Karnataka accounted for the maximum cases in the year 2013 and 2014.
• Genotypes: It has three genotypes: West African, East African and Asian genotypes.
• Most Indian cases before 1973 were due to Asian genotypes.
• However, Reunion outbreak was caused due to a mutated strain and is responsible for most of the current outbreaks in India as well as in other parts of the world.

Chikungunya Reasons for re-emergence:

• New mutation (E1-A226V): Chikungunya virus underwent an important mutation. Alanine in the 226 position of E1 glycoprotein gene is replaced by valine.
• New vector (Aedes albopictus): Mutated virus was found to be 100 times more infective to A.albopictus than to A. aegypti.

Chikungunya Laboratory diagnosis

• Viral isolation (in mosquito cell lines) and real time RT- PCR are best for early diagnosis.
• Serum antibody detection: MAC ELISA is the best serology test.
• Biological markers like IL-1β, IL-6 and are increased and RANTES levels are decreased in chikungunya infection.

Japanese B Encephalitis (JE)

Japanese B encephalitis is the leading cause of viral encephalitis in Asia, including India. It was first seen in Japan (1871); however, it is now uncommon in Japan.

Vector: Culex mosquito:

• C. tritaeniorhynchus is the major vector worldwide including India.
• C. vishnui is the next common vector found in India.

Transmission cycle: JE virus infects several animals and birds.

Two transmission cycles are predominant.

Pigs → Culex → Pigs

Ardeid birds → Culex → Ardeid birds

Chikungunya Animal hosts:

• Pigs are considered as the amplifier host. JE virus multiplies exponentially in pigs without causing any manifestation.
• Cattle and buffaloes may act as mosquito attractants.
  Horses are probably the only animal to be symptomatic and show encephalitis.
• Humans are considered as dead end; there is no man → mosquito → man cycle (unlike in dengue)
• Bird hosts: Ardeid (wading) birds such as herons, cattle egrets, and ducks are the important reservoir.
  Epidemiology
  Geographical distribution: Currently, JE is endemic in Southeast Asian region.
• It is common India, Nepal, Pakistan, Thailand, Vietnam and Malaysia.
• Because of immunization, its incidence has been declining from Japan and Korea.
• In India: JE has been reported since 1955. JE is endemic in 15 states; Uttar Pradesh (Gorakhpur district) accounting for the largest burden.
  In 2017, nearly 2,040 cases of JE were reported from India with 230 deaths.
  Maximum cases reported from UP followed by Assam, Manipur, West Bengal, Tamil Nadu, Tripura, Bihar, and Odisha.
• Age: 85% of cases occur in children below 15 years (but infants are not affected).
• Seasonal Variation: Common in rainy season with (maximum mosquito activity).

Chikungunya Clinical Manifestations

JE is the most common cause of epidemic encephalitis:

• Incubation period: Varies from 5–15 days.
• Subclinical infection is common: JE typically shows iceberg phenomena. Cases are much less compared to subclinical/inapparent infection with a ratio of 1:300-1000.
• Even during an epidemic, the number of cases are just 1–2 per village.
• Clinical course of the disease can be divided into three stages: Prodromal stage, Acute encephalitis stage and Late stage with sequelae of neurological deficits permanently.

Vaccine Prophylaxis

• Live attenuated SA 14-14-2 vaccine:
  • It is prepared from SA 14-14-2 strain
  • It is cell line derived; primary hamster kidney cells are commonly used.
  • Single dose is given subcutaneously, followed by booster dose after 1 year.
  • It is manufactured in China, but now licensed in India.
  • Under National Immunization Program, it is given to children (1–15 years) targeting 181 endemic districts of four states—UP, Karnataka, West Bengal and Assam.
• Inactivated vaccine (Nakayama strain and Beijing strain):
  • It is a mouse brain derived formalin inactivated vaccine.
  • It is prepared in Central Research Institute, Kasauli (India).
• Inactivated vaccine (Beijing P3 strain): It is a cell line derived vaccine.
• Combined vaccine: A genetically engineered JE vaccine that combines the attenuated
  SA14-14-2 strain and yellow fever vaccine strain 17D (YF 17D) virus; is under several clinical trials.

Dengue Viruses

Dengue virus is the most common arbovirus found in India. It has four serotypes (DEN-1, to DEN-4). Recently, the fifth serotype (DEN-5) was discovered in 2013 from Bangkok.

Dengue Viruses Vector

Aedes aegypti is the principal vector (most efficient vector) followed by Aedes albopictus. They bite during the day time.
Aedes acquires infection by feeding on viremic patients (from a day before to 5 days later, i.e. the end of the febrile period).

• Extrinsic incubation period of 8–10 days is needed before Aedes becomes infective.
• Once infected, it remains infective for life.
• Aedes can pass the dengue virus to its offsprings by transovarial transmission.
• Transmission cycle: Man and Aedes are the principal reservoirs.
• Transmission cycle does not involve other animals.

Dengue Viruses Pathogenesis

• Primary dengue infection occurs when a person is infected with dengue virus for the first time with any one serotype.
• Months to years later, a more severe form of dengue illness may appear (called secondary dengue infection) due to infection with another second serotype which is different from the first serotype causing primary infection.
• The severity of secondary dengue infection occurs due to a unique immunological phenomenon called antibody dependent enhancement (ADE), i.e. the non-neutralizing antibody produced against the first serotype will combine, cover and protect the second serotype
  from host immune response.
• ADE is remarkably observed when serotype 1 infection is followed by serotype 2, which also claims to be the most severe form and prone to develop into DHF and DSS.
• Serotype 2 is apparently more dangerous than other serotypes.
• Sequence of infection: Serotype 1 followed by serotype 2 seems to be more dangerous and can develop into DHF and DSS.
• Age: Though all age groups are affected equally, children less than 12 years are more prone to develop DHF and DSS.

Dengue Viruses Clinical Classifications

The traditional (1997) WHO classification, divides dengue into three clinical stages:

• Dengue Fever (DF): It is characterized by:
  • High fever (called as biphasic fever, break bone fever or saddle back fever)
  • Maculopapular rashes over the chest and upper limbs
  • Others: Frontal headache, Muscle and joint pains, lymphadenopathy, loss of appetite, nausea and vomiting
• Dengue Hemorrhagic Fever (DHF) is characterized by:
  • High continuous fever
  • Hepatomegaly
  • Thrombocytopenia (platelet count < 1 Lakh/mm3)
  • Raised hematocrit (packed cell volume) by 20%
  • Evidence of hemorrhages which can be detected by:
• Positive tourniquet test (> 20 petechial spots per square inch area in cubital fossa
• Spontaneous bleeding from skin, nose, mouth and gums
  Dengue Shock Syndrome (DSS): All the above criteria of DHF are present, plus manifestations of shock.
  The 2009 WHO classification grades dengue into two stages of severity of infection:
• Dengue with or without warning signs
  Severe dengue.
  Geographical Distribution
  Global Scenario: Tropical countries of Southeast Asia and Western Pacific are at highest risk.
  Situation in India:
  • Disease is prevalent in most of the urban cities/towns affecting almost 31 states/Union territories.
  • Between 2010–17, >6 Lakh cases with >1560 deaths have been reported from India.
    Maximum cases have been reported (in descending order) from West Bengal, Tamil
    Nadu, Punjab, Kerala, Delhi, Karnataka, and Maharashtra
  • In 2017, nearly 1,57,220 cases were reported; maximum of cases were reported from Tamil Nadu followed by West Bengal.
  • All four dengue serotypes have been isolated from India, but DEN-1 and DEN-2 are widespread. DEN-5 has not been reported yet.

Dengue Viruses Laboratory Diagnosis

• NS1 antigen detection: ELISA and ICT are available for detecting NS1 antigen in serum.
  • Early detection: NS1 antigen becomes detectable from day-1 of fever and remains positive up to 18 days.
  • Highly specific: It differentiates between flaviviruses. It can also be specific to different dengue serotypes.
  • Antibody detection:
  • In primary infection: IgM appears first after 5 days of fever and disappears within 90 days, followed by IgG (14–21 days of illness).
  • In secondary infection: Four fold rise of IgG antibody titers occurs.
  • MAC: ELISA is the most recommended test with excellent sensitivity and specificity. It can detect IgM and IgG separately.
  • Other antibody detection assays used previously are:
    • HAI (Hemagglutination inhibition test)
    • CFT (Complement fixation test)
    • Neutralization tests such as plaque reduction test, neutralization and microneutralization tests
• Virus detection: Dengue virus can be detected in blood from 1 day before the onset of symptoms and 5 days thereafter. It is done by:
  • Virus isolation can be done by inoculation into mosquito cell line or in mouse
  • Detection of specific genes of viral RNA by real time RT- PCR.
  • Each serotypes of dengue virus comprises of several genotypes which can be detected by molecular typing. A total of 13 genotypes have been detected so far.

Dengue Viruses Vaccine

Live-attenuated tetravalent vaccine based on chimeric yellow fever-dengue virus (CYD-TDV) has been developed by Sanofi Pasteur Company.

• This vaccine has been licensed for human use since 2015.
• It uses live attenuated yellow fever 17D virus as vaccine vector in which the target genes of all four dengue serotypes are integrated by recombinant technique.
• WHO recommends this vaccine to start in high burden countries (seroprevalence >70%).
• Currently, the vaccine is approved in Mexico, Philippines, Brazil, Indonesia, Thailand and Singapore. In India, it is not available yet.

Yellow Fever Virus

Yellow fever is endemic in West Africa and Central South America. It is not found in the rest of the World including India.

• Yellow Fever Virus Typing: At least seven genotypes of yellow fever virus have been identified based on genomic sequence, five in Africa and two in South America. There is only one serotype.
• Yellow Fever Virus Vector: Humans get the infection by the bite of Aedes aegypti or the tiger mosquito.
• Yellow Fever Virus Transmission cycle: Two major cycles of transmission have been recognized:
  • Jungle cycle: Occurs between monkeys and forest mosquitoes.
  • Urban cycle: Occurs between humans and urban mosquitoes (Aedes aegypti)
• India: Yellow fever has not invaded India yet. Various reasons have been hypothesized to explain the absence of yellow fever in India:
• Measures for the travelers taken at the international airports in India:
  • Unvaccinated travelers coming from endemic zone to India will be kept in quarantine for 6 days
  • Breteau index or the Aedes aegypti index should be less than one; surrounding 400 mt of airport.
• Cross reacting dengue antibody provides protection against yellow fever. However,yellow fever immunization does not protect from dengue.
• Clinical manifestations: Incubation period is about: 3–6 days. Common features include:
• Jaundice (hence the name yellow fever)
  • Mid-zonal necrosis and presence of councilman bodies
  • Intranuclear inclusions may be seen inside the hepatocytes called as Torres bodies.

Yellow Fever 17D Vaccine

It is a live attenuated vaccine, which is prepared from allantoic cavity of chick embryo:

• There is no risk of encephalitis (unlike the previously used Dakar vaccine).
• In India: It is prepared in Central Research Institute (CRI), Kasauli
• Strict cold chain has to be maintained –30°C to + 5°C.
• It is available in lyophilized form and has to be reconstituted with diluents such as physiological saline before use. Once reconstituted, it should be used within ½ hr.
• Dosage: Single dose, given subcutaneously
• Vaccine is effective within 7 days of administration, which lasts for 35 years.
• Validity of yellow fever vaccine certificate: Certificate is issued after 10 days of vaccination and renewed (i.e. reimmunization) every 10 years.
• Cholera and yellow fever vaccine interact with each other, hence shouldnot be given together (3 weeks gap to be maintained).
• Contraindication of yellow fever vaccine include: Children < 9 months, (< 6 months – during epidemic), pregnancy (except during outbreak), HIV, people with allergy to egg.

Kyasanur-Forest Disease Virus (KFD)

KFD virus was identified in 1957 from monkeys from the Kyasanur Forest in Shimoga district of Karnataka, India.

• Vector: Hard ticks (Haemaphysalis spinigera)
• Hosts:
• Reservoirs are the rats and squirrels
  • Amplifier hosts are the monkeys (KFD is known as Monkey’s disease).
  • Man is an incidental host and considered as dead end.
• Clinical Manifestation in humans: Incubation period varies from 3–8 days. First stage (hemorrhagic fever) occurs followed by second phase of meningoencephalitis.
• Seasonality: KFD is increasingly reported in dry months (January-June) which coincides with human activity in the forest.
• Situation in India:
  • Endemic in 5 Districts of Karnataka, Shimoga, North Kannada, South Kannada,Chikkamagaluru and Udupi
  • Largest outbreak had occurred in 1983–84. There is a declining trend of incidence after the initiation of vaccine in 1999. Currently only focal cases occur, except for the outbreak that occurred between December 2012 to March 2013 which witnessed 215
    suspects with 61 confirmed cases.
• Killed KFD vaccine: It is recommended in endemic areas of Karnataka (all villages within 5 km of endemic foci).
• Zika Virus Outbreak

Microbiology

• Zika virus belongs to family Flaviviridae and the genus Flavivirus.
• It is ssRNA virus, related to other viruses of same family such as dengue, yellow fever,Japanese encephalitis, and West Nile viruses.

History

• It is named after the Zika Forest, Uganda in 1947.
• Though it was wide spread among human population, was never a threat. Only 14 cases since discovery (1947) till 2007.
• The first outbreak was reported in 2007 in Yap Islands. Aedes hensilli was the predominant mosquito. 49 confirmed and 59 probable cases were reported.
• Monkeys are the reservoirs.

Epidemiology

Transmission

• Mosquito borne—Mainly spread by the Aedes aegypti but also by Aedes albopictus and other Aedes species.
• Mother-to-child transmission through placenta (common in first trimester), (during delivery rare, but possible)
• Sexual transmission is also possible (17 cases as of 26 August 2016)- Transmission is possible from:
  • Asymptomatic males to their female partners
  • Symptomatic female to her male partner
  • Longer shedding of Zika virus in semen.

Current Outbreak (2015-2016)

• Zika virus current outbreak began in April 2015 in Brazil.
• Subsequently it spread to other countries in South America, Central America, and the Caribbean.
• Imported cases have also been reported from Europe and the United States and Australia.
• As of 30th January 2017
  • 174,665 suspected cases, 528,157 confirmed cases and 18 deaths have been reported so far; out of which Brazil alone witnessed nearly 109,596 suspected and 200,465 confirmed cases.
  • Next to Brazil, other countries reported maximum cases are Puerto Rico, Colombia and Mexico.
• In February 2016, the WHO declared the Zika virus outbreak a public health emergency of international concern.

Situation in India

Three confirmed cases have been reported from Gujarat in 2017; first report from India. As the vector is prevalent, India has a higher risk of getting affected by ZIKV in near future.

Clinical Manifestations

• Incubation period: unknown, few days to 1 week
• Majority Asymptomatic-The asymptomatic: symptomatic ratio is 5:1
• Zika fever- Minor illness known such as fever and a rash, conjunctivitis
• Congenital transmission leads to newborn microcephaly
• In very few cases, Guillain-Barré syndrome have been reported from French Polynesia.

Lab Diagnosis

• IgM ELISA is available. But it cross-reacts with Dengue antibodies
• Plaque-reduction neutralization test -may be more specific.
• Multiplex real-time RT-PCR has been commercially available in India targeting the nonstructural 5 (NS5) region of ZIKV, non-structural protein 4 (nsP4) from CHIKV, and 3′untranslated region (3′UTR) of DENV 1–4.

Treatment and Vaccine

• No effective treatment or vaccine is available so far. Intense research is ongoing for vaccine development by many companies including India’s Bharat Biotech.
• An investigational Zika vaccine developed by NIAID and the NIH enters phase 1 clinical trials. It contains a genetically engineered plasmid—a small, circular piece of DNA—that encodes Zika virus protein.
• Only symptomatic treatment available such as fluid replacement and analgesics such as acetaminophen

Prevention

• Affected countries including Brazil, Colombia, Ecuador, El Salvador, and Jamaica advised women to postpone getting pregnant until more is known about the risks.
• Travel of pregnant women from other countries (including India) to Zika-affected countries has been restricted.
• Mosquito control measures- Same as that is done for Dengue prevention
• Infected patients should prevent mosquito bites for the first week of illness.
• CDC recommendation on Sex or pregnancy restriction:
  • Men – consider using condoms or not having sex for at least 6 months after travel (if don’t have symptoms) or for at least 6 months from the start of symptoms (or Zika diagnosis)
  • Women- consider using condoms or not having sex for at least 8 weeks after travel (if don’t have symptoms) or for at least 8 weeks from the start of symptoms (or Zika diagnosis)
  • Use condoms from start to finish, every time for vaginal, anal, or oral sex, or do not have sex for the entire pregnancy

Picornaviruses

Picornaviruses are very small (28–30 nm size) and nonenveloped viruses; divided into two major groups:

Enteroviruses: Transmitted by fecal-oral route. However, they do not cause intestinal symptoms but are associated with systemic manifestations. Examples:

• Polio (3 serotypes)
• Coxsackie A (1–24)
• Coxsackie B (1–6)
• Echovirus (1–33)
• Parechovirus (1–3)
• Enteroviruses (68–116)
• Enterovirus 72 is reclassified as Hepatitis A virus.

Rhinoviruses: Transmitted by respiratory mode. It is the MC cause of the common cold.

Polioviruses

Serotypes

• Type 1 (Brunhilde and Mahoney strains): Most common serotype to cause epidemics. This serotype is responsible for all the natural cases of poliomyelitis occurring globally at present
• Type 2 (Lansing and MEF-1 strain): It is the most antigenic and hence easiest serotype to be eradicated. No natural case has been reported since 1999. It is the MC serotype found
  among the VDPV (vaccine-derived poliovirus) strains.
• Type 3 (Leon and Saukett strain): No natural case caused by serotype-3 has been reported since 2013. However, It is considered the most common serotype to cause VAPP (vaccine-associated paralytic poliomyelitis)

Pathogenesis

• Transmission: MC is fecal-oral route, or rarely by inhalation or conjunctival contact.
• Receptor: Viral entry into the host cells is mediated by binding to CD155 receptors present on the host cell surface.
• Spread to CNS/spinal cord: Hematogenous spread (MC)>Direct Neural spread (occurs following tonsillectomy, where the virus may spread via glossopharyngeal nerve present in the tonsillar fossa).
• Site of action: Motor nerve ending, i.e. anterior horn cells of the spinal cord that leads to flaccid paralysis.
• Neuron degeneration: The earliest change in neurons is the degeneration of the Nissl body (aggregated ribosomes, normally found in the cytoplasm of neurons).
• Pathological changes are always more extensive than a distribution of paralysis.

Clinical Manifestations

The incubation period is usually 7–14 days. It manifests in four forms:

• Inapparent infection: Following infection, the majority (91–96%) of cases are asymptomatic.
• Abortive infection: 5% of patients develop minor illness (fever and malaise).
• Nonparalytic poliomyelitis: Seen in 1% of patients, presented as aseptic meningitis.
• Paralytic poliomyelitis is the least common form (< 1%):
• Characterized by: Descending asymmetric acute flaccid paralysis (AFP)
  • Proximal muscles are affected earlier than the distal muscles; paralysis starts at the hip → proceeds towards the extremities—which leads to the characteristic tripod sign (child sits with flexed hip, both arms are extended towards the back).
  • The site of involvement can be spinal, bulbospinal or bulbar.
  • Cranial nerve involvement is seen, but there is no sensory loss.

Risk factors: Paralytic disease is more common among:

• Older children and adults, pregnant women, and heavy muscular exercise
• Tonsillectomy predisposes to bulbar poliomyelitis
• IM injections increase the risk of paralysis in the involved limb.

Laboratory Diagnosis

• Specimen: Blood (3–5 days), throat swab (up to 1 week), CSF, feces (up to 6–8 weeks)
• Virus isolation: Primary monkey kidney cell line is used.
• Virus growth can be identified by various methods.
  • • CPE: Described as crenation and degeneration of the entire cell sheet.
    • Antigen can be detected and serotyped by neutralization with specific antiserum.
    • Specific gene detection by PCR
  • Sewage testing: Screening of sewage for detection of poliovirus (wild or vaccine virus) is routinely conducted under the polio eradication program. This is to verify whether the transmission is on-going or interrupted.
  • Cultures of CSF, serum, or throat swabs are positive less frequently, but indicative of disease.
  • Antibody detection: Neutralizing Antibody and CFT Antibody
• Molecular method: Real-time multiplex reverse-transcriptase PCR has been developed using primers from the VP1 region, which can detect and differentiate between various types of wild and vaccine polioviruses (VAPP and VDPV strains) directly from stool specimens.

Polio Vaccines

Two types of polio vaccines are in use (OPV and IPV). See the table given below.

Vaccine Vial Monitor

It is a tool to monitor the stability/potency of OPV (and efficiency of cold chain)

• It is heat sensitive label lining the OPV vial: Contains a ring of two circles—the outer circle is blue and the inner square is white
• WHO grading: The outer circle remains blue always, but the inner square may be white (grade-1) or change to light blue (grade 2), blue (grade 3), black/purple (grade 4)
• OPV is usable up to grades 1 and 2 and should be discarded for grades 3 and 4.

Vaccine-Induced Cases (VAPP and VDPV)

Vaccine-Associated Paralytic Poliomyelitis

• VAPP cases occur following OPV administration; due to some OPV strains undergoing mutation.
• VAPP strains are OPV-like isolates, which differ from OPV by < 1% gene.
• VAPP cases are ubiquitous in places where OPV is used extensively.
• VAPP can occur among OPV recipients as well as to their close contacts.
• However, VAPP strains are not capable of circulating in the community and do not cause outbreaks.
  This is largely because the spread of OPV-related virus is largely limited by high population immunity.
• VAPP rate: VAPP occurs at a rate of one case per 2.5 million doses of OPV.
• VAPP occurs more frequently:
  • Following the first dose of OPV than the subsequent doses
  • Among people with primary immunodeficiency disorder (↑ risk by 3000 fold)
• MC serotype associated with VAPP-Sabin type 3 (60%), followed by type 2.

Vaccine-Derived Polioviruses (VDPVs)

VDPV isolates exhibit a higher level of genetic divergence from their parental OPV strains at the VP1 sequence, which helps in their prolonged replication, and transmission.

• The genetic divergence of VDPVs from parental OPV strains is about
• 1% for Sabin types 1 and 3
  • 0.6% for Sabin type 2
• Isolates showing genetic divergence lower than this cutoff are considered OPV-like isolates.
• VDPV isolates are indistinguishable from wild polioviruses both clinically (due to regain of neurovirulence and phenotypically (by reversal of markers of attenuation)
• Most VDPV isolates belong to Sabin type 2 (90%) followed by type 1. This is because wild type 2 strains have already been eradicated and have not circulated in the community since 1999.

VDPVs can be categorized as:

1. Circulating VDPVs (cVDPVs): These strains are capable of person-to-person transmission in the community and can cause outbreaks in areas with low OPV coverage:
   • They pose the same threat to the community as that of wild polioviruses
   • Since 2000, cVDPV outbreaks have occurred in several countries, with a majority (90%) of reported cases associated with type 2 followed by type 1. All cVDPV reported in 2017 are type 2.
   • In 2013, over 700 strains of VDPVs have been isolated worldwide including India. Nigeria was worst affected, accounting for half of those strains.
2. Immunodeficiency-associated VDPVs (iVDPVs) are isolated from persons with primary immunodeficiency disorder:
   • They do not develop disease but excrete the iVDPVs for many years.
   • iVDPVs exhibit greater genetic diversity than cVDPVs some strains may be diverse by >10%
   • The extent of sequence divergence is proportional to the duration of the infection.
   • Unlike cVDPV, infections due to iVDPV cannot be prevented by high OPV coverage.
3. Ambiguous VDPVs (aVDPVs) are heterogeneous; They are either cVDPVs for which only 1 case isolate had yet been detected, or they may be sewage isolates obtained from developed countries with unknown sources (probably iVDPV).

Epidemiology

• Reservoir: Man is the only known reservoir. Most cases are subclinical.
• Clinical: subclinical ratio: For every clinical case, there may be 1000 children and 75 adults of subclinical cases.
• There are no chronic carriers. However, immunodeficient individuals may excrete the virus for longer periods.
• Source: Infective material such as stool and oropharyngeal secretions are the sources of infection.
• Age: Younger children and infants are more susceptible than adults. However, in developed countries, there is a shift of age; affecting older children.
• Period of communicability: Patients are infectious shedding the virus in the feces from 7–10 days before the onset of symptoms up to 2–3 weeks thereafter, sometimes as long as 3–4 months.

Polio Eradication

Poliomyelitis is now on the verge of eradication. This is attributed to the extensive immunization program being conducted globally.

Pulse Polio Immunization (PPI):

Two rounds of PPI (6 weeks apart) are scheduled every year during the winter season, where all children under the age of five years are vaccinated with OPV irrespective of their OPV vaccination status.

• PPI doses of OPV are considered as extra doses and they do not replace the OPV doses received under the routine national immunization schedule.

Polio Situation in the World

• Endemic countries: Currently polio is endemic only in two countries: Pakistan and Afghanistan.
• Countries no longer infected by wild poliovirus, but which remain vulnerable to international spread include Cameroon Equatorial, Guinea, Ethiopia, Iraq, Israel, Nigeria, Somalia, Syrian, Arab Republic.
• No. of cases reported in the World (till 8th January 2019):
• In 2018, 29 wild cases were reported globally (Afghanistan-21, Pakistan-8).
  However, there were 101 vaccine-derived cases (including cVDPV-1,2, and 3) reported from nonendemic countries such as the Democratic Republic of the Congo (20), Niger (9), Nigeria (33), Papua New Guinea (26) and Somalia (13).
• Currently, all-natural cases are due to type-1. Type 2 and 3 have not been reported since 1999 and 2013.
• India has been declared polio-free since 2014, the last natural case was detected three years back (Jan 2011).
• The Global Polio Eradication Initiative (GPEI) launched the ‘Eradication and Endgame Strategic Plan’ (2013–2018) aiming to wipe out polio from the entire world by 2018.

 

Coxsackieviruses

• Coxsackieviruses (named after the place of discovery; Coxsackie village in the USA) can be divided into two groups, A and B, based on their pathogenic potentials for suckling mice.
• Serotypes: Group A coxsackieviruses are typed into serotypes 1–24 (except 15, 18, and 23), and group B are typed into serotypes 1–6.

Rabies Virus

Morphology

• Bullet-shaped, enveloped virus. The envelope is embedded with glycoprotein antigen spikes.
• Nucleocapsid (made up of nucleoprotein) has a helical symmetry and comprises negative sense ssRNA
• Antigens: Rabies has two major antigens; Glycoprotein G and Nucleoprotein.

Pathogenesis

Transmission:

• Bite: Rabies virus is usually transmitted to humans by the bite of an infected animal.
• Animal bite: In India, dogs are responsible for about 97% of human rabies, followed by cats (2%), jackals mongoose, and others (1%) (except rat bites and human bites)
  • Bat bite (mostly goes unnoticed): Migrating fruit-eating bats are the most common bats that transmit rabies in America
  • Human-to-human transmission is theoretically possible but is extremely rare.
• Non-bite exposures are rare such as:
  • Lick on abrasion or mucosa
  • Inhalation of infected bats aerosols.
  • Corneal transplantation
• Route of spread: Viral replication in muscle → binds to nicotinic A ch receptors at NM junctions → spreads centripetally along peripheral motor nerves → dorsal route ganglia of spinal cord → infects brain neurons (brainstem and mental system) → centrifugal spread via sensory and autonomic nerves to the cornea, salivary gland, skin, and other organs

Clinical Manifestations

• Incubation period: 1–3 months (20–90 days)
• IP is shorter in children and upper limb bite and for short sighted people (than leg bite and taller people)
• Earliest symptom: Neuritic pain at bite site
• The clinical spectrum can be divided into three phases:
• Short prodromal phase
  • Acute neurologic phase: It presents in two forms: Encephalitic or dumb rabies
  • Coma and death: Occurs within 14 days of encephalitic rabies and 30 days of dumb rabies.

Laboratory Diagnosis

• Rabies antigen detection
  • Direct immunofluorescence test (direct-IF); also called as direct fluorescent antibody (DFA) test can be performed to detect rabies nucleoprotein antigens in specimens by using specific monoclonal antibodies tagged with fluorescent dye.
  • Because of its high sensitivity and specificity, DFA test is considered as the “gold standard” method for rabies diagnosis.
  • The best specimen is hair follicle of nape of neck (most sensitive).
  • Corneal impression smear: Positive in late stage with a sensitivity of 30%.

Viral Isolation

• Mouse inoculation: Intracerebral inoculation into suckling mice
• Cell lines: Mouse neuroblastoma cell lines and baby hamster kidney (BHK) cell lines are the preferred.

Antibody detection: Detection of CSF antibodies is more significant than serum antibodies as serum antibodies appear late and can also be present after vaccination.

Various antibody detection tests include:

• Mouse neutralization test (MNT)
• Rapid fluorescent focus inhibition test (RFFIT)
• Fluorescent antibody virus neutralization (FAVN)
• Indirect fluorescence assay (IFA)
• Hemagglutination inhibition test (HAI)
• Complement fixation test (CFT)

Viral RNA detection

• Reverse transcription-polymerase chain reaction (RT-PCR)
• The most sensitive and specific assay available at present for the diagnosis of rabies.

Negri body detection

• Negri body detection is pathognomonic for post-mortem diagnosis of rabies. However, it may not be detected in 20% of cases.
  Therefore, the absence of Negri bodies does not rule out the diagnosis of rabies.
• They are intracytoplasmic eosinophilic inclusions with characteristic basophilic inner granules.
• Sharply demarcated, spherical to oval, and about 2–10 µm in size.
• MC sites are neurons of the cerebellum and hippocampus; however, less frequently in cortical and brainstem neurons.
• Commonly used stains are Histological stains such as H and E and Sellers stains (basic fuchsin and methylene blue).

Prevention of Human Rabies

Postexposure prophylaxis (PEP) includes local wound care and both active and passive immunization.

Local Treatment

• Prompt cleaning of the wound, scrub with soap and water and apply antiseptics.
• Even if the patient reports late, care must be performed as the rabies virus is known to persist in the skin for a long time.
• Bite wounds are not sutured immediately.
• Confirmation whether or not the animal is rabid (for 10 days): Indicated in category II and III bites.
• Do not touch the wound(s) with a bare hand
• Do not apply irritants like soil, oil, lime, herbs, chalk, betel leaves, etc.

Passive Immunization
Human rabies immune globulin (HRIG): 20 IU/kg, maximum injected locally, rest IM in the gluteal region. It is indicated only in category III bites.

• Equine rabies immunoglobulin (ERIG)- It is given at a dose of 40 IU/kg. Being heterologous in origin (horse), it is associated with serum sickness; hence not in use.
• RIG should be administered within 24 hours; maximum up to the 7th day

Active Immunization (Rabies Vaccine)

Neural Vaccines: They are poorly immunogenic and encephalitogenic; hence not used.

• Semple vaccine: Derived from infected sheep brain
• BPL: Beta propiolactone-derived vaccine (Prepared in Coonoor)
• Infant mouse brain-derived vaccine

Non-neural Vaccines: Cell line derived, they are the recommended vaccine currently:

• Purified chick embryo cell (PCEC)
• Purified Vero cell (PVC)
• Human diploid cell (HDC).

Note:

• Though human-to-human transmission is rare; still PEP is offered as a precautionary measure following an exposure.
• Immunodeficient individuals must receive both Ig and vaccine for category 2 and 3 exposures and should be checked for serum antibodies after 14 days of vaccination if the facility is available.
• PEP is not contraindicated in pregnancy, lactation, infancy, old age, and any associated concurrent illness.

National Guideline on Rabies Prophylaxis

(Adapted from National Center for Disease Control, India)

Regimen for Post-Exposure Prophylaxis

• IM regimen or Essen regimen (1-1-1-1-1): Five doses (0.5 or 1 ml per dose) each given on days 0, 3, 7, 14, and 28 followed by a booster at 90 days. Day 0 indicates the date of the first dose of vaccine; not the date of exposure.
• ID Regimen (or Thai Red Cross Schedule) (2-2-2-0-2): This involves the injection of 0.1 ml of a reconstituted vaccine on two sites per visit on days 0, 3, 7, and 28.
• Potency: A single intramuscular dose should have a minimum potency of 2.5 IU.
• Site of injection:
• The deltoid region is an ideal site. The gluteal region is not recommended because fat retards the absorption of antigens.
  • Infants and young children: The anterolateral part of the thigh is the preferred site.

Regimen for Pre-Exposure prophylaxis

It is recommended for high-risk groups like laboratory staff handling the virus and infected material, clinicians or any person attending to human rabies cases, veterinarians, animal handlers, and travelers from rabies-free areas to rabies-endemic areas.

• Three doses of the vaccine: 0, 7, 28 days, and booster 2 years
• Antibody titer should be checked every 6 months for 2 years and thereafter every 2 yearly.
• A booster dose is given if the antibody titer is less than 0.5 IU/ml.

Regimen for Post-exposure Prophylaxis to Previously Vaccinated People

• Severe bite or titer unknown: 3 doses of vaccine: 0, 3, 7 days
• Less severe bite or titer > 0.5 IU/ml: 2 doses of vaccine 0, 3 days.

Epidemiology

Rabies is an enzootic and epizootic disease of both wild and domestic animals worldwide.

Worldwide: Rabies is endemic in > 150 countries. About 55,000 deaths occur due to human rabies each year. India accounts for the maximum number of cases (20,000 deaths/year).

• Source: Infected dog virus is present in saliva from 3-4 days before the onset of symptoms till the death of the dog.
• Rabies-free area: Defined as countries/areas where no cases have been reported in the last two years. Examples include:
  • World: Australia, Antarctica, Britain, Iceland, Ireland, China (Taiwan), Cyprus, Japan, Malta, New Zealand
  • India: Andaman and Nicobar, Lakshadweep
• Control of Urban Rabies: Elimination of stray dogs and mass immunization to at least 80% of dogs in an area.