Parasite effects on populations

1) Can Parasites wipe out entire populations?

- entire species

2) Can Parasites affect life cycles?

3) Mate selection?

4) Drive other mechanisms?

A. Bubonic Plague In Renaissance Europe

Bubonic plague (Yersinia pestis) had been absent from Western Europe for nearly a millenium when it appeared in 1348. Up to two thirds of the population of many of the major European cities succumbed to the plague in the first two years. Government, trade and commerce virtually came to a halt.

There was hardly a generation which did not experience a local, regional or pan-European epidemic for the next two hundred years. There was virtually no aspect of European society that was not affected by the coming of plague and by its duration.

At the most basic level, recurrent plague tended to skim off significant portions of the children born between infestations of plague, dampening economic and demographic growth in most parts of Europe until the late seventeenth century.

DISASTER STRIKES

Estimated population of Europe from 1000 to 1352.

1000 38 million 1100 48 million 1200 59 million 1300 70 million 1347 75 million 1352 50 million

25 million people died in just under five years between 1347 and 1352.

India: 1898-1908: > 500,000 died

What Conditions contributed to this situation

Large urban populations-Very congested housing conditions

Poor hygiene: water / garbage-Very high rat population

Bacteria entered susceptible rat population-Massive die off

Fleas abandoned ship-People in early stages moved away from area- took infection with them

Ring-a-ring-a-roses,A pocket full of posies;Ashes, Ashes, (A-tishoo, A-tishoo)We all fall down

Many have associated the poem with the Great Plague in England in 1665, or with earlier outbreaks of the Black Death in England. Interpreters of the rhyme before the Second World War make no mention of this.

By 1951, however, it seems to have become well established as an explanation for the form of the rhyme that had become standard in the United Kingdom. "The invariable sneezing and falling down in modern English versions have given would-be origin finders the opportunity to say that the rhyme dates back to the Great Plague. A rosy rash, they allege, was a symptom of the plague, posies of herbs were carried as protection and to ward off the smell of the disease.

Sneezing and coughing was a final fatal symptom, and 'all fall down' was exactly what happened." The line Ashes, Ashes in alternative versions of the rhyme is claimed to refer to cremation of the bodies, the burning of victims' houses, or blackening of their skin.

In its various forms, the interpretation has entered into popular culture and has been used elsewhere to make oblique reference to the plague.

For centuries, plague represented disaster for those living in Asia, Africa and Europe, where, it has been said, populations were so affected that sometimes there were not enough people left alive to bury the dead.

Because the cause of plague was unknown, outbreaks contributed to massive panic in cities and countries. The disease was believed to be delivered upon the people by the displeasure of the gods, by other supernatural powers or, by heavenly disturbance. Innocent groups of people were blamed for spreading plague and were persecuted by the panicked masses.

Could such a panic occur today?

1990s: A disease outbreak occurred in India. The rumour leaked out it was plague. Much movement of people away from the focus, and out of India. All international flights leaving India were met in N. America by health officials. In the US many people quarantined. Most international airports not equipped for these issues.

No imports or exports into the region, no tourism, no commerce.

Estimated cost $ 4-5 billion

How can we reduce parasite/disease problems in humans and animals?

Should we?

Can we?

Where are “new” diseases and Parasites coming from?

A detailed map highlighting the world's hotspots for emerging infectious diseases (EIDs) has been released. It uses data spanning 65 years and shows the majority of these new diseases come from wildlife. Conservation efforts that reduce conflicts between humans and animals could limit future outbreaks. 60% of EID events were caused by "non-human animal" sources, and 71% of these outbreaks were "caused by pathogens with a wildlife source".

PARASITE CONTROL

In the last 50 years the number of human cases of ascaris has gone up by 300 % from 400 million to 1200 million. The increase in hookworm disease has gone up 100 %, from 600 million in 1947 to 1200 million in 1997.

The other major change in parasitic disease in the last 50 years is an increase in opportunistic infections associated with immunosuppression and in particular AIDS, with parasites like Cryptosporidium, Toxoplasma, and Pneumocystis becoming life-threatening diseases

What do we do?

1) Nothing

2) Rational Intervention

3) Mass drug delivery

4) Vaccines

5) Take Bisc-318 and become paranoid

6) ????

Control Strategies

Ideally control methods should be integrated with knowledge of weak points of the parasites life cycle.

Intuitively it might seem that parasites with a direct life cycle might be easier to control than parasites with intermediate hosts, since only the definitive host and the external environment need to be considered. Safe sewage disposal will give satisfactory control of fecally transmitted parasites of man, e.g. Ascaris.

There are advantages with regard to control when dealing with one host life cycles, there is, however, an important disadvantage in that control of one host life cycles usually requires the co-operation of the infected individual or the co-operation of the owner of infected animals.

Co-operation from people even if they are likely to benefit directly can be difficult, so in practice parasites with heteroxenous life cycles may prove easier to control.

Who should do the controlling? Countries? UN?

Successful malaria control was done by professional spray teams who treated the inside of houses with DDT, without any direct involvement of the infected population.

Onchocerca control campaign in West Africa has been due to professional teams treating streams and rivers with insecticide to kill the vector.

Parasites with a direct life cycle usually have no capacity to multiply outside of their definitive host. Parasites with intermediate hosts often undergo asexual reproduction in the intermediate host, increasing biotic potential = difficult control

For the control of digeneans such as schistosomes, prevention of fecal contamination of snail habitats has to be almost perfect, since a single infected snail can shed thousands of cercariae.

Protozoa usually multiply within their definitive host, helminths do not. So low levels of helminth infection can be tolerated, but low levels of protozoan infections can build up to critical levels.

Prevention of Environmental Contamination

Antiparasite drugs are the most common method of parasite control and by reducing the number of adult parasites, this reduces environmental contamination.

Maximize benefits- prevent reinfection. This can be done by timing the treatment to coincide with a period when parasite transmission is low. Treatment can be followed by chemoprophylaxis to prevent reinfection if a suitable drug is available.

Sanitation has complemented drug treatment in almost all campaigns against fecally transmitted parasites. This is effective, provided the systems are maintained in working order.

Destruction of Free-Living Stages

Protozoan cysts, helminth eggs and infective larvae are often extremely resistant to toxic chemicals, so disinfecting areas is not very practical, unless you have animals in concrete pens which can be steam cleaned.

The destruction of nematode larvae on pasture is not very practicable, grazing with a non-host species helps i.e. alternating horses and sheep, liming fields will kill some larvae, the alternative is to plough up the field and start again.A broad range of microbial agents attack nematode eggs and larvae.

In biologically rich soils there are a variety of fungi that will attack parasite eggs. There are also a range of invertebrates which will eat and destroy parasite larvae, these include free-living nematodes, annelids and molluscs. Dung beetles that bury dung can also act as useful control agents. Anaerobic digestion kills eggs in sewage as does UV treatment.

Destruction of Intermediate Hosts and Vectors

This has often proved a very successful method of control, not least because it can be carried out by specialist teams and does not rely on public co-operation.

Environmental manipulation can eliminate habitats suitable for survival. Before the development of modern insecticides this was one of the major forms of control, for example, mosquito control. Remove breeding sites by drainage, land reclamation projects, removal of vegetation overhanging water, speeding up water flow in canals and periodic drainage and drying out of canals.

A variety of chemicals have been used to kill the molluscan host of schistosomiasis including CuSO4 and CaCN and more effective modern compounds such as niclosamide. Mollusciciding can be quite effective providing the water body is small.

Destruction of Reservoir Hosts

Most leishmania infections of man are zoonoses, i.e. they are caught from animals that are the natural hosts.

One approach to their control is destruction of the reservoir host. In the former USSR large scale destruction of gerbils has succeeded in providing control of Leishmania near towns and villages.

Destruction of free-ranging dogs is important in the control of leishmaniasis in China and also in the elimination of hydatid disease in Iceland. At one time the control of African trypanosomiasis was centred on the systematic destruction of wild reservoir hosts, particularly antelope. This did not work particularly well and was abandoned.

What about Foot and Mouth Disease in North America?

Prevention of InfectionSince parasite control is rarely 100% effective, prevention of infection represents an important tactic.

Many infective stages gain entry in drinking water, Cryptosporidium, Giardia, Dracunculus etc. These can be controlled by safe water supplies, the problem is that installation of water supplies is expensive and they have to be maintained.

Meat inspection of carcasses for cysticerci of Taenia solium and T. saginata is one of the oldest public health measures (dates back to 1400). In areas where infection is common carcasses are also inspected for Trichinella spiralis larvae. Thorough cooking or freezing will kill the infective stages of most parasites.

Wearing shoes, thus stopping the larvae burrowing through the skin can prevent hookworm infections.

Window screens, repellents and bed nets prevent mosquito bites. Ointments have been produced to try and prevent infection by hookworm larvae and by schistosome cercariae. Avoiding schistosome-contaminated water is another major factor as is education and a general increase in the standard of living.

Integrated Control

Integrated control is an overall approach, using a number of different tactics employed strategically based on a thorough knowledge of the life cycle and ecology of the parasite. It avoids over-dependence on a single method, and recognizes that no single method is likely to be 100 % effective, but in combination, complete control may be achieved.

Most control programmes are based on chemotherapy- drugs to rid the host of the infection or to prevent entry and establishment by parasite

Who pays to develop these drugs?

Is this drug development altruistic by drug companies?

Why is effective parasite chemotherapy so important ?

In absence of vaccines chemotherapy is the most cost-effective treatment method

1. Re-infection in endemic areas

Few drugs 100% effective

Drug Active against only a few stages

Parasite resistant to Drug

Drug cannot reach migrating parasite

2. Some drugs expensive

3. Serious side effects

4. Cannot be given orally

Potential Problems:

Drug treatment exerts selection pressure on Parasite population

Resistance due to:-

a) Presence/absence of single gene:

Result of high & frequent exposure to drug killing almost 100% of population

b) Polygenetic (combination of genes)

Drug treatments rarely 100% effectiveDrug treatment causes increase in frequency of resistant alleles in treated

population

Drug resistance: protozoa v helminths

Protozoa Long history of resistance Coccidiosis MalariaHelminths Overall less widespread resistance (intensive usage does lead to resistance)

Protozoa replicate more rapidly than parasitic worms

Anti-protozoan drugs used more extensively worldwide

 

Why develop parasite vaccines?

Part of a control programme

Advantages over drugs and disease prevention strategies

History of success in other diseases:

Diphtheria, Tetanus, Measles, Mumps, Rubella, Polio,

Hepatitis B, Yellow fever  

1. understand life–cycle of parasite → find best target stage 2. understand immune mechanisms stimulated by parasite

→ humoral /cellular response ?

3. Selected antigens must produce a protective response → not stimulate non-protective mechanisms Vaccine must stimulate a good response Good level of protection without boosting → using a simple delivery system

Currently very strong efforts to develop vaccines for the parasites that cause malaria (sporozoite, merozoite, gametocyte)Schistosomiasis, Hydatid disease, Leishmania

What do all these intervention strategies try to do?

RR00 represents the average number of secondary infections generated by one primary case in a susceptible population

Can be used to estimate the level of immunization or behavioural change required to control an epidemic

R0 = βH α + µ + b

β =transmission rate, H= number of hostsα = parasite induced host mortality (a measure of virulence)µ= parasite mortality rate within the host, b=natural host death

A detailed map highlighting the world's hotspots for emerging infectious diseases (EIDs) has been released. It uses data spanning 65 years and shows the majority of these new diseases come from wildlife. Conservation efforts that reduce conflicts between humans and animals could limit future outbreaks. 60% of EID events were caused by "non-human animal" sources, and 71% of these outbreaks were "caused by pathogens with a wildlife source".

What do we do with enzootics?

Bury or burn

Climate linked to plague increase

Up to 3,000 cases of plague are reported each year

Climatic changes could lead to more outbreaks of bubonic plague among human populations, a study suggests.

Nepal's government has been accused of "inaction and apathy" after it emerged that 10 out of 250 endangered elephants are suffering from tuberculosis (TB).

Malaysia mystery virus unmasked The killer virus which killed at least 100 people in Malaysia and led to the slaughter of thousands of pigs has been identified.

Malaysian medical authorities initially blamed a mosquito-borne disease called Japanese encephalitis for the deaths.

The Nipah virus was the cause of the mystery illness. It is thought to be a brand new disease that has crossed only recently from animals to people. In a separate report, doctors in Singapore say the Nipah virus was also responsible for an outbreak of fever and drowsiness among abattoir workers there

in March this year.

Blame game amid Rio dengue crisis

In one of Rio's poorest shanty towns, city fire officers make their way through narrow polluted lanes, in what is the front line of the fight against dengue.

Their job is to treat the stagnant water and cover exposed tanks that are a breeding ground for the mosquito that spreads potentially fatal dengue virus.

More than 60 people have died in the state of Rio de Janeiro so far this year, and more than 60 other deaths are being investigated. More than 40,000 people have been treated for dengue. For the people who live in the Community of Coroado, especially the children, the risks are all too obvious. A large container filled with rubbish sits by the road, while there are large pools of water, as well as exposed drains and sewage.

A detailed map highlighting the world's hotspots for emerging infectious diseases (EIDs) has been released. It uses data spanning 65 years and shows the majority of these new diseases come from wildlife. Conservation efforts that reduce conflicts between humans and animals could limit future outbreaks. 60% of EID events were caused by "non-human animal" sources, and 71% of these outbreaks were "caused by pathogens with a wildlife source".

Avian flu

SARS

Human flu

Swine flu

MERS

What is Next?

New death from SARS-like virus in Saudi: WHO 2013 GENEVA -- Another person suffering from a SARS-like virus has died in Saudi Arabia, the World Health Organization said Thursday, bringing the worldwide number of fatalities from the mystery illness to seven. The Saudi health ministry had informed the U.N.'s health body that the patient had been hospitalized on Jan. 29 and had died on Feb. 10, WHO said in a statement.

A laboratory had confirmed on Feb. 18 that the person had died from the so-called novel coronavirus, or NCoV, it added.

This brings to 13 the number of cases of the virus that have so far been reported to the WHO since it was first detected in the middle of last year, with six previous fatalities — three in Saudi Arabia, two in Jordan and one in Britain.

The news comes just days after a person suffering from the virus died in hospital in central England on Sunday.

That patient, who had a pre-existing health condition, was one of three people in the same family with the virus, which appeared to have been caught by one of the family members during a recent visit to the Middle East and Pakistan.

First known deaths from H7N9 bird flu in ChinaBEIJING – Two Shanghai men have died from a lesser-known type of bird flu in the first known human deaths from the strain, and Chinese authorities said it wasn’t clear how they were infected but there was no evidence of human-to-human transmission. A third person, a woman in the nearby province of Anhui, also contracted the H7N9 strain and was in critical condition.

H7N9 bird flu is considered a low pathogenic strain that cannot easily be contracted by humans. The overwhelming majority of human deaths from bird flu have been caused by the more virulent H5N1, which decimated poultry stocks across Asia in 2003.

The World Health Organization is “closely monitoring the situation. There is no evidence of human-to-human transmission, and transmission of the virus appears to be inefficient, therefore the risk to public health would appear to be low.

The 87-year-old victim became ill on Feb. 19 and died on Feb 27. The other man, 27, became ill on Feb. 27 and died on March 4. Scientists have been closely monitoring the H5N1 strain of the virus, fearing that it could mutate into a form that spreads easily among people, potentially sparking a pandemic. So far, most human cases have been connected to contact with infected birds.

SALMON, Idaho (Reuters) - A federal judge on Monday denied a request from environmentalists to halt the execution of buffalo at Yellowstone National Park, a ruling that clears the way for scores of buffalo to be shipped to slaughter.

More than 500 buffalo, or bison, have been corralled in recent weeks in the park after their search for food caused them to wander from the park into Montana, where ranchers fear the bison will transmit brucellosis to cows. The disease can cause cows to miscarry their young.

Federal and state agencies that oversee the nation's last purebred herd of wild bison planned to kill straying bison when conservation groups sued to stop the slaughter. Government officials have been testing the penned bison for exposure to brucellosis as they awaited the court's decision. By Friday, testing had revealed 137 of the 513 corralled buffalo had the antibodies for the bacterial disease. The park plans to kill the 137 and any other bison that have been exposed to brucellosis.

Environmental groups said Monday they plan to appeal the ruling by U.S. District Judge Charles C. Lovell. There are some 3,700 bison in Yellowstone.

What would you do?

How do you stop transmission from bison to cattle and vice versa?

Hoof and Mouth Disease

Duck Plague

Chronic Wasting Disease

Bovine tuberculosis

Avian malaria

Plague

Mad Cow disease

Avian Cholera

Amphibian decline and deformations

500 people are infected with Ebola virus in the Congo. What do you do?

50,000 people are infected with P. falciparum in Uganda in the midst of a civil war. What do you do?

50,000 people are disabled (physically and mentally) in BC. What do you do?

Populations are increasing everywhere, creating conditions in which disease can flourish. Should some groups not be able to have children? Should any regulations be in place to reduce family size?

Is any individual worth more than another?