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Lecture - 10 (1st year DDS Program)


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Factors which have an influence on the appearance
of new pathogens related to humans

1. Pathogens
New emerging pathogens – they appeared for the first time among human population during last 2 or 3 decades;
Pathogens which emerge once again – they occured earlier, but during last 20 years increase of diseases caused by them is bigger. The area of their occurance is also much wider nowadays.

2. New emerging pathogens of human (in %)
viruses and bacteria 74 % - the biggest amount;
protozoa 11%;
fungi 9%;
helmints 6%.

3. Types of infections
only zoonotic – all human infections are caused by pathogens of animals which are the reservoir of pathogens. The animals are the vectors of infection. There is no transmission between people;
mainly zoonotic - animals are the reservoir of the pathogens and a source of human infections. There are sporadic transmissions between people, and sometimes some epidemic may occur;
partially zoonotic - some infections are from animals and transmission of a pathogen between people occurs often and it may have endemic character;
originally zoonotic - originally pathogen was attacking animals, now it is attacking mainly or only human;
non-zoonotic - there is no evidence for existence of pathogen in animals. Infected humans are the reservoir of pathogen.

4. Why pathogens appear once again?
a) Changes in genome of pathogen
:
gene mutations;
gene transfer between organisms.
b) Environmental changes:
Climate warming up:
more wide spreading of diseases which occur endemic in countries with warm or tropical climate;
increase of the number of vectors (mosquitos, ticks).
Changes caused by human activity:
cutting trees and afforestation will cause bigger contact with vectors;
development of water resources (new way of pathogen transmission, it will also cause creation of ideal conditions to live for pathogens and their hosts);
increase of pollution of environment with human and animal droppings (bigger amount of invasive forms of pathogens);
creation of new big hospitals: central air-conditioning (aerobiocontamination), nearness of hospital wards (increase of hospital infections), transmission of pathogens: individuals with lower immunity.
c) Factors of the host:
genetic conditions;
increasing number of individuals with immunodeficiency (HIV infection, after transplan-tations, therapy against tumour);
demographic changes: increase of human population, bigger number of children and older people in population, increase of number of people who live in cities;
behaviour changes: migrations (many reasons), international tourism (fast trasnport between countries and continents (1mln of people per 1 day), changes in food habits, culture changes.

5. Immunodeficiency - Inborn or acquired (not healthy food, stress, radiotherapy, HIV and other infections, chronic diseases, alcoholism, pregnancy).

6. The bird flu
virus belongs to Orthomyxoviridae family;
every bird species is potentially endangered (infection mostly without symptoms in wild birds, infection is deadly for poultry);
virus is known from 100 years (first identification of virus took place in Italy);
neuraminidase as a result of activity of this enzyme the virus is removed from infected host cell; and hemagglutinine is glycoprotein which is responsible for binding of the virus to the host cell;
there are 15 known subtypes;
the reason of infection in human is by contact with excrements or excretions of sick birds.

How did it happen that the bird flu virus is a threat? (3 theories)
recombination of the viruses in the host cells, which were infected by the bird flu virus and a human flu virus simultaneously (it is possible when the contact between people and breeding birds is very close);
mutations of the viruses (in birds) which are the cause for changes of the antigens and creation of a deadly H5N1 type;
possibility of gene mix in swine;

migrating aquatic birds have a big role to play in distributing the virus among the other birds geographically;
the pandemic may occur if the virus gain ability to pass from man to other man.

7. Legionellosis – Legionnaires disease
Foster microclimate contribute to bigger morbidity for legionellosis which is caused by bacterium Legionella pneumophilia;
First cases in 1947. It is a pathogen which emerge once again;
First outbreak in 1976 (USA, American Legionconvention in Philadelphia).

Symptoms: pneumonia, chills, cough, headache, tiredness, loss of apetite;
Sources: air-conditioning, large air-conditioning cooling towers, respirators, showers, bubble baths.

8. Borreliosis – Lyme disease
Borrelia burgdorferi – bacterium transferred by ticks;
First outbreaks near Old Lyme, USA (1982);
Existed earlier in Europe as a „bullseye” rash (first symptom – circle rash in the place where the tick bited his victim);
Symptoms: I stage - „bullseye” rush; II stage - passing organ symptoms; III stage - damage of nervous and movement systems, death;
New emerging disease
The climate warming up increased number of ticks;
Afforestation increased the number of ticks and their spreading;
Economical and behavioural factors: people build houses near the forests; many people want to have recreation allotment - contact with animals and ticks is much more closer;
Ticks may cause also: brain fever (inflammation), babesiosis - Babesia canis (protoza).

How to avoid tick’s attack?
by wearing a suitable clothes covering our body;
after spending some time in the forest, or on a meadow, try to look all over your body and search for ticks;
remove the tick as fast as you can and disinfect the place where it was on your skin;
use some anti-ticks substances;
avoid of places in which ticks may live.

9. Cryptosporidiosis is caused by protozoan parasite - Cryptosporidium sp.
1910 - first description of C. muris;
1912 - first description of C. parvum (in mice);
1955 - first description C. meleagridis (the cause of high death rate of turkeys);
1971 - C. parvum is the cause of diarrhoea in calves;
1976 - the first two incidents with infection of C. parvum in humans;
1983-1992 - increase of interest among doctors (detection of cryptosporidiosis is often in people with HIV or who have contact with calves);
1993 - the biggest outbreak connected with water (Milwaukee, USA). The sources of drinking water linked to this outbreak included surface water (lakes, rivers, streams), well water, spring water, 403 thousand people infected, more than 100 people died, and there were 150 mln $ losses.

Very good example of new pathogen which emerge once again and attacks new hosts. Genetic diversity of Cryptosporidium and its ability to break the biological barrier between many species makes this pathogen very universal and dangerous. Its adaptation abilities are its great weapon.

Occurance of Cryptosporidium in the environment
cryptosporidiosis is often all over the world in young ruminants (calf, lamb - high level of environmental pollution);
USA - cattle excrete 4.6 tons of oocysts per 1 year;
the cattle have a big role in spreading cryptosporidiosis;
amount of pollution produced by 10 thousand cattle units is equal to amount of pollution produced by 110 thousand people;
oocysts are very resistant for environmental factors like cold or heat and they are resistant for most of commercial anti-oocyst disinfection substances. They stay alive in droppings, sewers, until they get into water resources.

What contributes to biological pollution of environment
storeging and scattering of manure;
carrying off the agricultular and communal sewage;
pasturing animals near water resources;
sewage from slaughtehouse;
recreational horse riding.

Species of Cryptosporidium and their hosts
C. andersoni - cattle;
C. baileyi - chicken, man;
C. canis - dog, man;
C. felis - cat, man, cattle;
C. galli - birds;
C. hominis - man;
C. meleagridis - turkey, man;
C. molnari, C. nasorum - fish;
C. muris - rodents, man;
C. parvum - over 150 mammal species, man;
C. saurophilum, C. serpentis, C. varanii - reptiles;
C. wrairi - Guinea pig.

10. Cyclosporidiosis is caused by protozoan parasite Cyclospora
1881 - first description and creation of Cyclospora type;
1902 - next confirmations about presence of the parasite; later (early years of XX century) 6 species of Cyclospora in reptiles were discovered;
1979 - first cases with presence of a parasite in human.
Symptoms of cyclosporidiosis: sever diarrhea with frequent, sometimes explosive bowel movements, loss of appetite, loss of weight, muscle aches, vomiting, tiredness.
In 1996 raspberries, lettuce and basil were the source of the cyclosporidiosis outbreak in USA and Canada.
New emerging pathogen. The first human cases were reported in 1979, but cases began being reported more often in the mid-1980s.

11. Microsporidiosis is caused by microsporidia (Protozoa)
intracellular parasites which can infect broad range of vertebrates and invertebrates;
over 1000 species are known;
wasting, severe, chronical diarrhea, loss of weight, kidney disease, brain disease, lung inflammation;
very common in people with HIV and after transplantation, and among the people with other immune deficiency;
spores are released from gastrointestinal and urinary tracts of infected animals;
14 microsporidian species which infect people;
discovered 100 years ago, first case of human microsporidiosis reported in 1959, ten cases described until 1985;
pathogen which emerge once again and suits itself to „special” host (AIDS).

12. The reasons of drug resistance
genetic variability of pathogens;
variability in sensitivity for activity of many medicaments;
genetical, immunological, physiological factors of infected host;
often and common use of medicaments;
not following after doctors recommendations about how to use medicaments.

REMEMBER
DRUG RESISTANCE IS A CAUSE FOR APPEARING
OF MANY DISEASES ONCE AGAIN

 Author: Piotr Nowosad date: 2020-05-13  print    back  
 
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