MedBankers.

2008-02-03T20:23:00.000+08:00

Medbankers would like to thank all our lecturers, Mr Alvin Poh, Dr Khin, Mr Loh and Ms Michelle Chew for their guidance in our final year studies. THANK YOU !!!

Pls remember us... ^^

MMIC PBL - part 2 (avian flu)

2008-01-28T01:48:00.000+08:00

Avian Influenza (Bird Flu):

Introduction:

Influenza viruses are segmented, negative-sense, single-stranded RNA viruses of the family Orthomyxoviridae and are divided into A, B and C.

Avian Influenza or bird flu refers to the different strains of influenza virus adapted to birds, a specific host. This is known as Influenza A virus, whereby all subtypes are adapted to birds. Generally, most avian influenza viruses are noninfectious for most species of birds, and are usually asymptomatic (no symptoms) if infectious. Hence, they do not pose much of a threat despite being highly transmissible.

However, domestication of birds/poultry has produced subtypes of avian species that are vulnerable to the viruses that rapidly mutate, causing many bird-related deaths. These become dangerous when the virus mutates and is transmissible to humans, such as the H5N1 virus. Other such viruses includes the H1N1 (Spanish flu) and the H9N2 (Hong Kong flu). Alternatively, viruses may mutate and infect an intermediate host such as the pig/swine, which support reassortment of genes that create new subtypes, before going on to infect humans.

As of 2004, Indonesia has had outbreaks of the H5N1 virus – avian flu. This strain is deadly to humans and usually spread through contact with poultry and domesticated birds like the fighting cock in Thailand. Indonesia has had outbreaks of H5N1 viruses, mainly from the poultry breeding farms. Typically, H5N1 transmission is restricted to from bird to humans. However in 2006, there was a case of human to human transmission of H5N1 versus between a group of small families, but the spread appears to have died off. H5N1 can last indefinitely at a temperature dozens of degrees below freezing.

Hence, this blog will concentrate on H5N1 virus as it is the most relevant in indonesian context as well as given time, and threatening to human life.

Strains of Influenza A:
Subtypes of influenza A as previously mentioned are based on antigenic relationships of the hemagglutinin (H) and neuraminidase (N) surface glycoproteins, two proteins on the surface of the virus that allow it to enter and exit host cells.
o Each virus has one HA and one NA protein, potentially in any combination
o Sixteen different hemagglutinins (H1-H16) and nine different neuraminidases (N1-9) have been identified to date.
o Typically, most avian flu is restricted to bird to bird transmission. The most deadly being H5N1 strain as it can spread from bird to human.

commons.wikimedia.org > wiki > Flu_und_legende_color_c.jpg

Virulence:

Virulence is determined based on antigenic properties of the strain.
Highly pathogenic avian influenza (HPAI) viruses causes systemic disease with rapid death rate, mostly of the H5 or H7 subtypes
Low pathogenic avian influenza (LPAI) viruses cause a localized infection with little or no disease.
Virulence factor is also correlated with the hemagglutinin cleavage site – all HPAI have multiple basic amino acids (arginine and lysine) at the HA0 cleavage site, while LPAI have 1 or 2 amino acids. Multiple amino acid sites allow for a wider range of protease cleavage, resulting in higher amounts of reassortment, increasing virulence and susceptibility in other animals. This also allows for host protease to act on HPAI, causing it to replicate systemically, damaging vital organs and tissues, which results in severe disease and death as seen in H5N1.

Pathogenicity:
Spread to humans via contact, potentially airborne (incubation period is longer, less adapted to droplet transmission):
- Directly from birds or from avian virus-contaminated environments to people (consumption of poultry products, direct contact with live poultry – bodily fluids such as blood, salvia etc and contaminated food sources).
- Through an intermediate host, such as a pig.
Typically develops 1 to 5 days following exposure.

- H5N1 virus particles enter blood stream through contact with chickens/ poultry. Virus attaches to cell surface sialic acid via receptor site on the haemagglutin (HA) site. Adhere to endothelium in respiratory tract.
- Internalised by receptor mediated endocytosis within cellular endosomes
- Viral envelope and cell membrane fuses, releases viral particles into cytosol.
- Cytosol acidic pH causes conformational changes in HA structure to form HA2, that binds to membrane to open M2 ion channel.
- Ions from endosome enters virus particle, triggering another set of conformational changes to HA, releasing viral nucleocapsids into the cell cytoplasm.
- Viral transcription occurs in the nucleus by viral encoded polymerase, consisting of a complex of 3 P proteins. This is activated by RNA polymerase II that caps and methylates the 5’ terminal.
- Viral proteins such as NS and NP are synthesized
- NS proteins interact with M proteins for nuclear export of viral RNPs.
- Templates for viral synthesis remain coated in nucleocapsid which are neither trunucated or methylated
- Viral mRNA are synthesized by viral encoded polymerase using positive template strand.
- Individual viral components arrive at budding sites by different routes
- Nucleocapsid is assembled in the nucleus and moves out to cell surface
- Glycoproteins HA and Na are synthesized in the endoplasmic reticulum, modified and inserted into the plasma membrane
- M protein serves as a bridge, linking nucleocapsid to sytoplasmic ends of glycoproteins
- Progeny virons bud off from cell when HA is cleaved to HA1 and HA2 by proteolytic enzyme from host. NA removes terminal sialic acid from cellular and viral surface viral proteins, facilitating release of viral particles from cell.

Signs and symptoms:
Common:
- Cough
- High fever (typically > 38°C)
- Headaches
- myalgia (muscle ache/pain)
- malaise (general discomfort)
- Sore throat
- Shortness of breath
- Diarrhoea
- A relatively mild eye infection (conjunctivitis), sometimes the only indication of the disease.

Severe signs and symptoms:
- Viral pneumonia
- Acute respiratory distress (the most common cause of bird flu-related deaths)
- Seizures

Laboratory Diagnosis:

Samples to be taken: Nasal washings, gargles, throat swabs. Within 3 days of onset of symptoms.
Sample conditions: Held at 4oC until inoculation into cell culture (freezing/thawing reduces viral recovery).

Isolation methods: embryonated eggs, monkey kidney cells.

1) Viral isolation
Viral isolates can be identified by hemagglutination inhibition, that rapidly determines influenza type and subtype. Test serum/culture fluid with hemagglutination inhibitor to check for presence. If results are negative, make a passage into fresh culture as influenza is typically fastidious and grows slowly.

2) Fluorescent antibodies
For rapid diagnosis, cell cultures on coverslips may be inoculated and stained 1 or 2 days with monoclonal antibodies to respiratory agents. Positive confirmed with use of single fluorescent antibody.
Alternatively, a more rapid diagnosis with less sensitivity is directly using fluorescent antibody on nasal aspirate.

Sample: Blood, serum.

3) Serology
Normal individuals will produce influenza antibodies during infection, such as antibodies to hemagglutinin, neuraminidase, nucleoprotein and matrix. These can be deteced by ELISA or hemagglutination inhibition (HI). These are performed using the patient’s serum extracted from blood stream. ELISA is more sensitive than other assays, while HI enables pin pointing of influenza strain. However, this method is dependant on patient’s antibody response system.

Necessary precautions:
1) Avoid contact with live birds, and all forms of poultry:
- Chickens, ducks, turkeys and geese and their feces, feathers and pens if at all possible.
2) Avoid poultry products in Indonesia, as cases of H5N1 have been reported there.
3) All foods from poultry, including eggs should be cooked thoroughly. Egg yolks should not be runny or liquid. Influenza viruses are destroyed by heat, hence cooking temperature for poultry meat should be 74oC (165 F).
4) Avoid cross contamination of other foods by use of separate kitchen utensils and surfaces exposed to raw poultry.
5) Wash hands with soap and water after any poultry contact.
6) Avoid live food markets.

Treatment:
Antivirals:
Suppress virus, keep it from replicating and infecting within the host. Must be taken soon (often within 48 hours following infection).
Neuraminidase inhibitor:
Mode of action consists of blocking the function of the viral neuraminidase protein, preventing the virus from reproducing.
1. Relenza
2. Tamiflu

Vaccination:
Vaccines expose an individual to a weakened/dead virus to stimulate antibody production against it, so that immune system can fight off infections should it arise.
There are at least 15 different strains of avian flu and they are constantly mutating, hence vaccination may not prove to be effective for long.
Live vaccines (attenuated, weakened):
- Requires less antigen (active ingredient) than killed vaccine.
Live vaccine may contain too few copies of the weakened virus to trigger an immediate immune response.
However, once inside the host, the virus can replicate to render it detectable by the immune system and trigger an immune response.
Does not require injection – oral consumption will do.
Killed virus (inactivated):
Must be injected – only route to administer them that will bring them into contact with the immune system.
Requires larger dosage than live vaccines due to its lack of ability to multiply within host.
3. Recombinant vaccine:
Genetically engineered vector (usually a low virulence virus) to express H5N1 protein antigen on surface, to stimulate immune response (production of antibodies).

References:
sciencedaily.com > releases > 2007 > 08/070828154944.htm
cidrap.umn.edu > cidrap > content > influenza > avianflu > news > dec3005halvorson.html
evolution > berkeley.edu > evolibrary > news > 51115_birdflu
http://www.cbc.ca/> news > background > avianflu > protection.html
http://www.cdc.gov/ > ncidod > EID > vol10no4/03-0396.htm

Cheers,

Debra, TG02

Protozoa pathogens – post 2 (Eunice)

2008-01-27T16:45:00.000+08:00

Plasmodium species [1]

(Picture taken from http://en.wikipedia.org> malaria parasite> plasmodium falciparum)

Characteristics: In P. falciparum, only early trophozoites and gametocytes are seen in the peripheral blood. The parasitised RBCs are not enlarged and it is common to see multiple infected RBCs.

Toxoplasma species [2]

(Picture taken from http://en.wikipedia.org> toxoplasma)

Characteristics: Tachyzoites are the motile, asexually reproducing form of the parasite.

Helminths – Wuchereria bancrofti [3]

(Picture taken from http://en.wikipedia.org> helminths> wuchereria bancrofti)

Characteristics: The microfilaria is sheathed and the tail is tapered to a point. The nuclear column loosely packed, the cells can be visualized individually and do not extend to the tip of the tail.

Leishmania species [4]

(Picture taken from http://google.com> images> leishmania)

Characteristics: Leishmania cells have two morphological forms: promastigote (with an anterior flagellum) in the insect host, and amastigote (without flagella) in the vertebrate host.

Gardia, Cryptosporidium and Cyclospora [5]
Image of Gardia:

(Picture taken from http://en.wikipedia.org> gardia)

Image of Cryptosporidium

(Picture taken from http://en.wikipedia.org> cryptosporidium)

Image of Cyclospora

(Picture taken from http://en.wikipedia.org> Cyclospora)

REFERENCES
1) http://en.wikipedia.org> malaria parasite

2) http://en.wikipedia.org> toxoplasmosis

3) http://en.wikipedia.org> helminths> wuchereria bancrofti

4) http://en.wikipedia.org> leishmania

5) Foodborne pathogens: hazard, risk analysis and control / edited by Clive de W. Blackburn and Peter J. McClure

PBL blog 2 - Viruses part 2

2008-01-27T15:51:00.000+08:00

In this post, I will be concentrating on 5 main viruses as a follow up on the previous post.

1. Chikungunya

Caused by: Alphavirus of the Togaviridae family. (1)

Transmission: Ades aegypti mosquito vectors (1)

Pathogenesis: Sylvatic cycle.

Chikungunya virus under scaning electron microscope. Picture taken from: http://www.flickr.com/photos/ajc1/1257163357/

Symptoms: Petechial (small red dot) or maculopapular (bumpy bumps) rash around the limbs and trunk. Polyarthritis resulting in debilitating pain causing contortions in affected joints, headache, slight photophobia (sensitivity to light), fatigue, nausea, vomiting and muscle ache. There are many other symptoms depending on age and severity of the disease. Note that the disease is similar to dengue. (2)

Women suffering from severe joint pains in a hunched position. Picture taken from : http://www.semp.us>
publications>biot_reader.php?BiotID=339

Suitable precaution: Avoid mosquito bites such as wearing long sleeves and long pants to cover the limbs and to treat clothes with permethrin or alternatively, use insect repellents.

2. SARS (Severe Acute Respiratory Syndrome)

Caused by: SARS coronavirus

<---- Sars coronovirus under scanning electron microscope. Picture taken from: http://pathmicro.med.sc.edu/graduate/corona-cdc.jpg

Transmission: Spread mainly by close person-to-person contact. When an infected person coughs or sneezes, droplets of mucus or saliva that contain the virus are sent through the air. Once these droplets land on the mouth, nose or eyes, an infection can occour.
Kissing, touching, sharing utensils for eating and drinking, or talking with an infected person is also a risk factor for infections. if you travel to countries with SARS. There is no treatment for SARS. Scientists are testing treatments and vaccines. (8)

Pathogenesis:

Week 1: Fever, muscle aches and other symptoms that generally improves after a few days.
Week 2: Patients experiences recurrance of fever, diarrhea and oxygen desaturation (characterised by breathing difficulties) and severe worsening of condition of the patient may occur. (6)

Damage of alveolar (lung) tissue due to SARs infection. Picture taken from http://pathmicro.med.sc.edu/virol/coronaviruses.htm

Week 3: Patients requires ventilatory support and some may develop end-organ damage and severe lymphopenia (abnormally low levels of lymphocytes, which is a type of white blood cells) resulting in death.

Symptoms: Patients are present with a high fever of > 38.0°C, including chills, headache, dizziness, rigors (shaking due to high fever), malaise (general feeling of discomfort), muscle aches.

Suitable precaution: Observe hygiene such as frequent washing of hands and avoid sharing of utensils.

Caring for a SARs patient in the ICU. Notice the attire of the clinicians and the pathogenecity of the virus. Picture taken from: http://www.bact.wisc.edu/themicrobialworld/SARS.html

3.Tick borne encephalitis

Caused by: Tick-borne encephalitis virus (TBEV) which is a member of the Flaviviridae family.

Transmission: Tick bites of the ixodes species

Pathogenesis: Ticks are the hosts and the reservoir of the virus. TBEV chronically infects ticks and is transmitted from larva to nymph to adult ticks. TBEV infects humans when tick bites during the peak period of april to november. (9)

Tick responsible for TBE. Picture taken from: http://www.hqusareur.army.mil/htmlinks/Press_Releases/2007/May2007/08May2007-01.htm

Symptoms: Asymptomatic for the first 2 weeks. Non-specific symptoms including fever, muscle aches, anorexia, headache, nausea and vomitting.

Suitable precaution: Vaccination and using insect repellents and protective clothing such as long sleeves, long pants and covered shoes.

4. Influenza (Flu)

Caused by: Family of Orthomyxoviridae viruses known as the influenza viruses.

Transmission: From infected bird droppings, coughing and sneezing of infected person, creating aerosols of the virus and contact with contaminated surfaces. (5)

<--- Model of the influenza virus. Picture taken from: http://www.3dscience.com/Resources/Influenza_Virus.php

Pathogenesis: Entry to host cells followed by binding of the host's columnar epithelial cells at the respiratory tract. Fusion with the cell's membrane and release of viral RNA which replicates within the nucleus, synthesizing structural and envelope proteins then releasing virions infecting neighbouring cells.

Symptoms: Fever, extreme coldness, sore throat, muscle pains, severe headache, coughing, weakness, fatigue, nasal conjestion, redden irritated watery eyes, coughing, sneezing and general discomfort.

Suitable precaution: Influenza vaccinations and observe hygiene.

5. Hepatitis A

Caused by: Hepatovirus hepatitis virus (HAV) (3)

Transmission: Contaminated food and water.

Symptoms: Nausea, diarrhea, fever, jaundice, fatigue, abdominal pain, loss of appetite and weight loss. (4)

Hepatitis virus under the scanning electron microscope. Picture taken from: http://zh.wikipedia.org/wiki/%E7%94%B2%E5%9E%8B%E8%82%9D%E7%82%8E

Suitable precaution: Vaccination and throughly cook food, drink boiled water and observe personal hygiene.

References:

1. Chikungunya: http://en.wikipedia.org/wiki>Chikungunya

2.
http://www.cdc.gov>ncidod>dvbid>Chikungunya>chikvfact.htm

3. Hepatitis A: http://www.cdc.gov>ncidod>diseases>hepatitis>a>fact.htm

4. Hepatitis A: http://en.wikipedia.org/wiki>Hepatitis_A

5. Influenza: http://en.wikipedia.org/wiki>Influenza

6. SARs: http://www.sarsreference.com>sarsref>diag.htm

7. SARs: http://www.sarsreference.com>sarsref>prevent.htm

8. SARs: http://www.sarsreference.com>sarsref>trans.htm

9.Tick bourne encephalitis:
http://www.cdc.gov>ncidod>dvrd>spb>mnpages>dispages>TBE.htm

Yeng Ting
TG02

Water borne protozoa_elaine(2nd blogging)

2008-01-27T14:32:00.000+08:00

Protozoa: single-celled parasites
--> they are unicellular eukaryotes, meaning that they are charactistics organelles. They are relatively large and some are visible with the naked eye. They occupy a vast array of habitats and niches and have organelles similiar to those found in other eukaryotes cells as well as specialized organelles. Protozoa usually reproduce asexually by binary fission. (3)

Infection with parasites is a major cause of morbidity and mortality in tropical and semitropical countries
http://www.dpd.cdc.gov/dpdx/HTML/Cyclosporiasis.htm
Transmission:
-->faecal-oral
-->arthropod vectors

-->intermediate hosts e.g. fishes or snail

Prevention:

-->Treat drinking water with high efficiency filtration and/or chemical disinfection such as chlorination or ozonation (4)

1) Giardia Lamblia (giardiasis):

--> A flagellated protozoon and an important cause of diarrhea worldwide. (1)

--> is a flagellated protozoan parasite that colonises and reproduces in the small intestine, causing giardiasis.

--> Giardiasis does not disseminate haematogenously, nor does it spread to other parts of the gastro-intestinal tract, but remains confined to the lumen of the small intestine. Giardia trophozoites absorb their nutrients from the lumen of the small intestine, and are anaerobes.
http://www.brown.edu/Courses/Bio_160/Projects2004/rotavirus/Epidemiology.htm
[Route of infection]: Faecal-oral

[Pathogenesis]: cysts of Giardia Lamblia have been demonstrated in the drinking water. Ingestion of cysts—the resistance, infective stage—is followed by the production of trophozoites in the upper small intestine. Trophozoites cause irritation, which leads to gastrointestinal symptoms.

[Clinical features]
Symptoms: diarrhea, mild to severe, with characteristic light-coloured fatty tools; abdominal pain: cramps, with flatulence and epigastric tenderness; anorexia
Malabsorption: steatorrhoea is not common and may lead to the full-blown malabsorption syndrome.

2) Cryptosporidium Parvum (Cryptosporidiosis): (1)

-->Cryptosporidium is a protozoan pathogen of the Phylum Apicomplexa and causes a diarrheal illness called cryptosporidiosis.

-->Human infection is often acquired as a result of animal slurry contaminating water supplies.
http://www.cbu.edu/~seisen/CadSu0402.htm
[Transmission]:
The infective stage is the oocyst, passed in faeces: transmitted person-to-person, animal-to-person or via contaminated water.

[Clinical features]
Symptoms: self-limiting diarrhea in the immunocompetent individual.

3) Isospora Belli:

--> humans seem to be the only host of this parasite, which infects the small intestine. (2)
http://www.tropeduweb.ch/factsheets/fs_parasital_class_protozoa.html
[Transmission]
Faecal-contaminated food and water

[Clinical Features]
In the immunocompetent infection is often asmptomatic and the diarrhea, when present, tends to be mild.

[Pathogenesis]

In the immunocompetent, infection is generally asymptomatic or a self-limiting gastro-enteritis. However, in chronic infections, severe diarrhoea and fat malabsorption can occur.
Infection in immunocompromised individuals ranges from a self-limiting enteritis to severe diarrhoeal illness resembling that of cryptosporidiosis.

4) Cyclospora Cayetanensis (Cyclosposiasis): infect the small intestines (1)
http://www.tmd.ac.jp/med/mzoo/parasites/General/cyclospora.gif
[Transmission]
The infective stage is the oocyst passed in faeces (waterborne)

[Clinical features]
Symptoms: diarrhea, remitting and relapsing, sometimes lasting as long as 6 weeks; malabsorption in some cases; weight loss

5) Entamoeba Histolytica (amoebiasis): a common infection in tropical countries such as Indonesia where the sanitation is poor. (2)
http://parasite.tmu.edu.tw/lab-pict/Protozoa/page/image6.html
[Route of infection]
Faecal-oral, owing to contaminated water

[Clinical features]
Diarrhea, progressing rapidly to bloody diarrhea accompanied by fever and painful abdominal cramps, symptoms may pesist into a chronic relapsing state. Sometimes progresses to dilatation of the colon, with the risk of intestinal perforation.

[Complication]
Amoebic absecess owning to spread to the liver causing painful enlargement and accompanied by high fever, raised white cell count and high ESR.

ReferencesBook:

(1) Medical microbiology 4th edition. written by patrick R. Murray, Ken S. Rosenthal, George S. Kobayashi, Micheal A. Pfaller

(2)Book: microbiology of waterborne disease. written by S L Percival, R M Chalmers

(3) University at Albany School of Public Health. (2004). sph>oned>lesson6.pdf/">sph>oned>lesson6.pdf/">sph>oned>lesson6.pdf/">http://www.albany.edu>sph>oned>lesson6.pdf

(4) Wikipedia, the free enycyclopedia. wiki>giardia_lamblia/">wiki>giardia_lamblia/">http://en.wikipedia.org>wiki>Giardia_lamblia

(5) Carlo Denegri Foundation. Intestinal parasites. html>iso1.htm/">http://www.cdfound.to.it>hTML>iso1.htm

PEI SHAN - Fungal pathogens 2nd post

2008-01-26T20:22:00.000+08:00

Most possible fungal agents that might be encountered by the soldiers - Beware!!!

1. Dermatophytes
-Epidermophyton

Epidermophyton floccosum
Image from: http://www.mycology.adelaide.edu.au/

-Microsporum

Microsporum fulvum