Day 7: polio, japanese encephalitis, zika

Class on Saturday? Yayy… but like actually yay.

Today we had a lecture on polio, then Japanese encephalitis, then zika.

Newer classification of enteroviruses is A,B,C and D, polio is part of human enterovirus c group.

Although poliomyelitis is largely eradicated in the world (Western Hemisphere, Europe, SE Asia, and pacific region), it still circulates primarily in Afghanistan, Nigeria, and Pakistan. Like other neuroinvasive

viruses, west nile, Japanese encephalitis – the majority of people exposed to this virus are asymptomatic, ~ 95%. 4-8% will develop flu like illness (abortive polio) – headache, sore throat, fever, N/V and fatigue. This is due to a second major viremia. It most often gets into us by pharynx and has several phases. Gets in through oropharynx, then intestinal phase (where it reaches peyers patches), lymphatic phase, viremia phase, and neurologic phase in some individuals.

In about 0.1% of all polio infections, selective destruction of motor neurons, causing severe back, neck and muscle pain and motor weakness develops.  After this invasion of CNS, the virus un-coats, replication occurs, and motor neurons die, leading to paralysis of motor fibers. It can also cause a brainstem encephalitis and respiratory insufficiency. A percentage of patients will develop bulbar symptoms.

Vaccination took about a majority of the talk. Polio virus has 3 strains (1,2,3). Currently, two is no longer circulating thus is not needed in current vaccines. Also, given a bivalent type 1 and 3 oral vaccine leads to superior immunogenicity of strains 1 and 3 compared to trivalent vaccine. Vaccine associated paralytic poliomyelitis is still a concern with the oral polio vaccine, occurring in about 1/900,000 people. As there is vaccine associated polio, there is a plan to eradicate and cease all oral polio vaccination by 2021 in order to prevent this.

The both vaccines are efficacious, interestingly, diarrhea at the time of oral polio vaccine has been associated with decrease seroconversion.

From uptodate:

In May 2014, the international spread of wild poliovirus was declared by the World Health Organization to be a Public Health Emergency of International Concern (PHEIC). Temporary recommendations to reduce the international spread of wild poliovirus were issued, and the situation has been reassessed at three-month intervals thereafter. In February 2017, the following temporary recommendations were issued [54,56,57]:

●All residents and long-term visitors (>4 weeks) traveling from Pakistan should receive a booster dose of OPV or IPV between 4 weeks and 12 months prior to international travel and should have the dose documented. Those undertaking urgent travel (ie, within 4 weeks) who have not received a dose of poliovirus vaccine in the previous 4 weeks to 12 months should receive a dose of OPV or IPV at least by the time of departure.

●All residents and long-term visitors (>4 weeks) traveling from Nigeria, Pakistan, Afghanistan, and Lao People's Democratic Republic should be encouraged to receive a booster dose of OPV or IPV 4 weeks to 12 months prior to international travel; those undertaking urgent travel (ie, within 4 weeks) should be encouraged to receive a dose at least by the time of departure.

●Travelers who are vaccinated should be provided with an International Certificate of Vaccination or Prophylaxis to serve as proof of vaccination.

So I should probably get my adult booster dose.

Japanese encephalitis was discussed, the most important cause of viral encephalitis in Asia. Throughout the talk, it became apparent that it is very similar to west nile virus (as well as St. Louis encephalitis). Features associated with both is that it is most commonly asymptomatic, rarely progresses to neurologic dysfunction, it can cause encephalitis, parkinsonism, acute flaccid paralysis, it a flavirvirus and also is transmitted by the culex mosquito.

<1% of JEV infections cause symptomatic neuroinvasive disease. Rule of 1/3rds was discussed with 30% recovery completely, 30% mortality, and 30% with morbidity.

Above are some MRI pictures of a 2 year old child from Northern India who had a relatively rapid decline, not performing developmental milestones, who had basal ganglia involvement of MRI highly suggestive of JE.

Humans are dead end hosts, meaning there is not sufficient viremia for a human to infect a mosquito.  The particular culex that transmits the virus (culex vishnui subgroup) breeds in rice fields, and other shallow pools of water. It is a nighttime biting mosquito like anopheles and mainly feeds outdoors. Pigs are a key host as they develop high levels of viremia, and in Asia, pigs are kept close to human dwellings. Pigs are often asymptomatic.

Diagnosis: basal ganglia involvement on MRI can be seen, BL thalamic lesions are most commonly described, can be specific in the right context. Like west nile, CSF IgM is the best test to diagnose it (ELISA). The serum antibodies can remain elevated for some time and not necessarily indicative of acute infection.

The United States Advisory Committee on Immunization Practices (ACIP) recommends JE vaccine for travelers who plan to spend a month or longer in endemic areas during the Japanese encephalitis virus (JEV) transmission season. Vaccination should be considered for short-term travelers (<1 month) if they plan to travel outside of an urban area and have an increased risk of JEV exposure

The recommended primary immunization schedule for JE-VC is two doses administered intramuscularly on days 0 and 28; the two-dose series should be completed at least one week prior to travel.

Zika talk occurred in the afternoon, not too much new here for myself, but a reminder - still alot to learn, generally for a couple wanting to conceive waiting 2 months for a women to conceive, and 6 months for a man are conservative recommendations.