Please, help with this question. I know that it can have few different answers, but, please, tru to answer it from your master-specailist point of view.

[RomanRodinskiy]

Analyse the strategies of exploitation of the host and ways of avoiding the immune response by parasites and suggest, in your opinion, the best parasite among the existing ones and ways of fighting against such "elusive Avenger"?

[mistermack]

3 hours ago, RomanRodinskiy said:

Analyse the strategies of exploitation of the host and ways of avoiding the immune response by parasites and suggest, in your opinion, the best parasite among the existing ones and ways of fighting against such "elusive Avenger"?

There is no good or bad. But if you take survival of a parasite's genes as their purpose, then the parasites that don't damage their hosts are the best. A lot of viruses eventually end up not damaging their hosts, and become part of their dna, so I guess those would qualify as being the 'best' parasites. 

[RomanRodinskiy]

It's not about which parasites are best for their master at all. The question means that the best parasite is the one that best avoids its host's immune system, which makes it invisible. And so the question needs to learn which parasites can boast such characteristics and what processes and mechanisms are responsible for it.

 

[mistermack]

5 hours ago, RomanRodinskiy said:

It's not about which parasites are best for their master at all.

It seems pretty obvious that parasites that damage or kill their hosts will eventually become less numerous, if they adversely affect the survival of the population of the host. Generally the ones that do the most damage are ones that jump from one species to another, like the covid virus did. You then get an evolutionary race of parasite vs immune system. In the end, the most successful parasites will be the ones that can evolve quickest, to keep ahead of the game. 

[TheVat]

Toxoplasmosis is a champ.  Half the world has it, and most never have symptoms, and it spreads from cat litter boxes.  

The parasite's survival is dependent on a balance between host survival and parasite proliferation. T. gondii achieves this balance by manipulating the host's immune response, reducing the host's immune response, and enhancing the parasite's reproductive advantage. Once it infects a normal host cell, it resists damage caused by the host's immune system, and changes the host's immune processes.  As it forces its way into the host cell, the parasite forms a parasitophorous vacuole (PV) membrane from the membrane of the host cell. The PV encapsulates the parasite, and is both resistant to the activity of the endolysosomal system, and can take control of the host's mitochondria and endoplasmic reticulum.

[NTuft]

On 3/14/2023 at 7:02 AM, TheVat said:

Toxoplasmosis is a champ.  Half the world has it, and most never have symptoms, and it spreads from cat litter boxes.  

The parasite's survival is dependent on a balance between host survival and parasite proliferation. T. gondii achieves this balance by manipulating the host's immune response, reducing the host's immune response, and enhancing the parasite's reproductive advantage. Once it infects a normal host cell, it resists damage caused by the host's immune system, and changes the host's immune processes.  As it forces its way into the host cell, the parasite forms a parasitophorous vacuole (PV) membrane from the membrane of the host cell. The PV encapsulates the parasite, and is both resistant to the activity of the endolysosomal system, and can take control of the host's mitochondria and endoplasmic reticulum.

Bravo, +1. T. gondii is also notable for changing behavior of the host. Infected mice will make themselves vulnerable to predation by cats. Infected humans have behavioral and psychological symptoms. And,  A brain parasite is making wolves into pack leaders, scientists say. 

 

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[...]the infected canids surveyed by the Yellowstone Wolf Project for the study appeared to be up to 46 times more likely to become pack leaders in the wake of infection. This may be because T. gondii has been shown in other mammals — including, in humans in particular — to increase testosterone levels, the research notes.

Cat Carrier

The wolves infected with the parasite were also, per the study, 11 times more likely to venture into new territory than their uninfected counterparts — a macho move if there ever was one, as this dangerous behavior tends to quite literally expand the pack's turf.

Effects of Toxoplasmosis on human behavior
 

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Abstract
Although latent infection with Toxoplasma gondii is among the most prevalent of human infections, it has been generally assumed that, except for congenital transmission, it is asymptomatic. The demonstration that latent Toxoplasma infections can alter behavior in rodents has led to a reconsideration of this assumption. When infected human adults were compared with uninfected adults on personality questionnaires or on a panel of behavioral tests, several differences were found. Other studies have demonstrated reduced psychomotor performance in affected individuals. Possible mechanisms by which T. gondii may affect human behavior include its effect on dopamine and on testosterone.

Toxoplasmosis and behavioural changes

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Abstract Nearly one-third of the planet's population is affected by Toxoplasma gondii infection. In ophthalmology, toxoplasmosis is even considered to be the most common cause of posterior uveitis of infectious origin. Humans are only an intermediate host and T. gondii needs to infect cats for its sexual reproduction. All the elements increasing the risk of predation by the definitive host are then favourable to the parasite. Numerous experimental animal model studies have shown that T. gondii infection is associated with predatory risk behaviours such as an attraction of infected mice to cat urine. Infection with the parasite is associated with a demethylation of the promoters of certain genes in the cerebral amygdala of the intermediate hosts, modifying dopaminergic circuits associated with fear. Similarly, T. gondii has been linked to behavioural changes in humans. Toxoplasma infection is classically associated with the frequency of schizophrenia, suicide attempts or "road rage". A more recent study shows that toxoplasma infection prevalence was a consistent, positive predictor of entrepreneurial activity. Fear of failure would be less important in infected individuals, who are more willing than others to start their own business. These elements shed interesting light on behaviours and their possible relationship with toxoplasmosis, which is generally considered benign in adults.

emphasis added

Though contact with an infected cat's feces is a risk factor, infection is more likely transmitted by consuming undercooked meat or soil exposure, according to this study:

Sources of toxoplasma infection in pregnant women: European multicentre case-control study

Quote

Results
Risk factors most strongly predictive of acute infection in pregnant women were eating undercooked lamb, beef, or game, contact with soil, and travel outside Europe and the United States and Canada. Contact with cats was not a risk factor. Between 30% and 63% of infections in different centres were attributed to consumption of undercooked or cured meat products and 6% to 17% to soil contact.

emphasis added