POLIO

Question 1

Compare and contrast the oral polio vaccine and the injectable polio vaccine (3)

Answer 1

• OPV = Sabin, live attenuated, 3 strains (now dropping to 2), risk of mutation, sterilising immunity, IgA in gut
• IPV = Salk, inactivated, 3 strains, no risk of mutation, immunity = disease prevention, IgG in blood

Question 2

Name the two (2) available vaccines against polio, state the type of vaccine, and state how they are administered in South Africa according to the routine vaccination schedule (10x½ = 5)

Answer 2

OPV – live attenuated – birth, 6 weeks; IPV – killed – 6w/10w/14w/18m

Question 3

Name the aetiological agents responsible for poliomyelitis (1½)

Answer 3

Poliovirus 1, 2 and 3

Question 4

Describe the pathogenesis of poliomyelitis (5)

Answer 4

Virus gains access to the body via ingestion. It replicates in gut associated lymphoid tissues. In some individuals this may be followed by a viraemia and haematogenous spread to the CNS. Lytic infection of motor neurons in the anterior horns of the spinal cord leads to a lower motor neuron weakness of muscles supplied by affected motor neurons (Flaccid paralysis)

Question 5

State what percentage of infected individuals develop paralysis (½)

Answer 5

1%

Question 6

Name the most appropriate sample to send to the laboratory to diagnose poliomyelitis (½)

Answer 6

Stool sample

Question 7

State how poliomyelitis has been brought under control (1)

Answer 7

Through the use of 2 effective vaccines.

Question 8

Patient returned a week ago from a 3 week visit to his relatives in Northern Nigeria. This region has been experiencing an outbreak of poliovirus type 1. He has had a fever, muscle pain in his back & legs & now weakness has developed in both legs, with no sensory loss.

Give a brief outline of the pathogenesis of poliomyelitis (3)

Answer 8

(½ for any relevant point) Polioviruses are enteroviruses and transmission is via the faecal oral route. After initial replication in the GIT there is haematogenous dissemination to the CNS. The patient may present with meningitis. In about 1 in 100 patients paralytic poliomyelitis occurs. Here, the virus invades and destroys anterior horn cells of the spinal column, so causing paralysis. Can also occur in bulbar form.

Question 9

How would you confirm the diagnosis of polio? (½)

Answer 9

Culture stool sample (not CSF)

Question 10

Name a public health administrative procedure that you would need to follow for this condition (polio)? (½)

Answer 10

Notifiable disease or surveillance

Question 11

How has poliovirus been controlled in South Africa? (1)

Answer 11

Universal vaccination against poliovirus (Sabin vaccine) starting at birth.

Question 12

Describe the oral and injectable polio vaccines available today, and mention differences in immunity acquired through the use of each (4)

Answer 12

Oral polio vaccine = live attenuated; 3 strains (1,2,3), with 2 eradicated, and 1+3 left in the vaccine; IgA/ mucosal/ gut immunity also. IPV = inactivated, injected, 3 strains, humoral immunity only.

Question 13

State when each of the polio vaccines is given in the public healthcare sector in South Africa (2)

Answer 13

OPV = birth + 6 weeks. IPV = 10 weeks, 14 weeks, 18 months