Diseases caused by protozoa Questions in English

(B) During the malaria infection,the Plasmodium parasite feeds on the haemoglobin present in the host's red blood cells.
As the parasite digests the globin protein,it releases the haem group.
The toxic haem is converted into a non-toxic crystalline pigment called haemozoin.
Therefore,haemozoin is derived from the haem part of haemoglobin.

(C) The life cycle of $Plasmodium$ involves an asexual phase in humans and a sexual phase in the mosquito.
In the human $RBCs$ (erythrocytes),the sporozoites transform into trophozoites.
The early trophozoite stage is characterized by a large central vacuole that pushes the nucleus to the periphery,giving it the appearance of a 'signet ring'.
This stage marks the beginning of the erythrocytic schizogony cycle within the $RBCs$.

(A) The incubation period is the time interval between the entry of the parasite into the human body through the bite of an infected female $Anopheles$ mosquito and the appearance of the first clinical symptoms (fever).
For $Plasmodium \ vivax$, the incubation period typically ranges from $10$ to $17$ days, with an average of about $14$ days.
Therefore, $14$ days is the most accurate option provided.

(A) $Entamoeba \ histolytica$ is a protozoan parasite that inhabits the human large intestine.
In the lumen of the colon,the parasite undergoes encystation to form cysts,which are then passed out in the feces.
However,when the parasite invades the intestinal wall and enters the bloodstream,it can reach extra-intestinal sites such as the liver,lungs,or brain.
In these extra-intestinal tissues,the parasite exists in the trophozoite form and does not undergo encystation.
Therefore,it does not form cysts in the liver.

(C) $Trypanosoma cruzi$ is a protozoan parasite that causes Chagas disease, also known as American trypanosomiasis.
It is primarily found in South and Central America.
Kala-azar is caused by $Leishmania donovani$, while African Sleeping Sickness is caused by $Trypanosoma brucei$.

(B) Malaria is caused by different species of the protozoan parasite $Plasmodium$.
In India,$Plasmodium \ vivax$ is the most common species responsible for malaria infections.
While $Plasmodium \ falciparum$ causes the most severe and malignant form of malaria,$P. \ vivax$ has the highest prevalence across the country.

(D) $Trypanosoma \text{ } gambiense$ is the causative agent of African sleeping sickness in humans.
It is a protozoan parasite that is transmitted to humans through the bite of the tsetse fly, specifically the species $Glossina \text{ } palpalis$.

(D) Rhoptries are specialized secretory organelles found in the apical complex of Apicomplexan parasites, including $Plasmodium$.
These organelles are essential for the invasion of host cells.
Both the $Merozoite$ and the $Sporozoite$ stages of $Plasmodium$ possess an apical complex containing rhoptries.
However, in the context of standard biological examinations, the $Sporozoite$ is the most commonly cited stage characterized by the presence of these organelles for the invasion of liver cells.

(A) $Entamoeba \text{ } histolytica$ is a protozoan parasite that causes amoebiasis in humans.
The life cycle involves two main stages: the cyst and the trophozoite.
The $Trophozoite$ stage is the active, motile, and feeding form of the parasite.
This stage invades the mucosa and submucosa of the large intestine, where it multiplies and causes tissue destruction, leading to the formation of characteristic flask-shaped intestinal ulcers.

(A) The incubation period is the time interval between the entry of the parasite into the human body and the appearance of the first clinical symptoms (fever).
- $P. falciparum$ has an incubation period of approximately $8-12$ days.
- $P. vivax$ has an incubation period of approximately $10-17$ days.
- $P. ovale$ has an incubation period of approximately $10-17$ days.
- $P. malariae$ has the longest incubation period among these,typically ranging from $18-40$ days or even longer.
Therefore,$P. malariae$ exhibits the highest incubation period.

(C) Black water fever is a severe complication of malaria characterized by massive hemolysis (destruction of red blood cells) and hemoglobinuria,which turns the urine dark or black.
This condition is primarily associated with infection by $Plasmodium \ falciparum$.

(D) The life cycle of $Plasmodium$ species (such as $Plasmodium$ $vivax$,which causes benign tertian malaria) involves multiple stages within the human host.
$1$. Pre-erythrocytic cycle: Occurs in the liver cells (hepatocytes) after the sporozoites are injected by the mosquito.
$2$. Erythrocytic cycle: Occurs in the red blood cells (RBCs) where the parasite multiplies,leading to the clinical symptoms of malaria.
$3$. Post-erythrocytic cycle: Refers to the secondary development in liver cells (exo-erythrocytic schizogony) that occurs in some species,contributing to relapses.
Therefore,all these cycles are part of the complex life cycle of the parasite.

(B) When a female $Anopheles$ mosquito bites an infected person,it ingests various stages of the malaria parasite $(Plasmodium)$ along with the blood.
In the mosquito's stomach,the digestive enzymes break down and digest most of these stages,such as $Sporozoites$,$Merozoites$,and $Erythrocytes$.
However,the $Gametocytes$ (male and female gametes) are resistant to these digestive enzymes and survive to undergo further development (fertilization) in the mosquito's gut.
Therefore,the correct answer is $Gametocytes$.

(B) The life cycle of $Plasmodium$ is digenetic,meaning it requires two hosts to complete its life cycle.
$1$. The primary host is the human,where the asexual cycle (schizogony) occurs.
$2$. The secondary or intermediate host is the female $Anopheles$ mosquito,where the sexual cycle (gametogony and sporogony) occurs.
In biological terminology,the host where the sexual phase occurs is often referred to as the definitive host,while the host where the asexual phase occurs is the intermediate host. In the context of the parasite's development outside the human body,the mosquito acts as the exogenous host.

(A) Maurer's dots are irregular,coarse,reddish-brown or green-stained structures observed in the cytoplasm of human $RBCs$ (erythrocytes) infected with $Plasmodium \ falciparum$.
These dots are a diagnostic feature of $P. \ falciparum$ infection during the erythrocytic cycle.

(C) The life cycle of $Plasmodium$ involves two hosts: the female $Anopheles$ mosquito and the human.
In the female $Anopheles$ mosquito,sexual reproduction occurs,and it acts as the definitive or primary host.
In humans,the asexual cycle (schizogony) occurs,and humans act as the intermediate host.

(A) In the life cycle of $Plasmodium$,the sexual phase occurs in the gut of the female $Anopheles$ mosquito.
When the mosquito ingests blood containing gametocytes,the $Microgametocytes$ (male gametocytes) undergo a process called exflagellation.
During this process,the nucleus of the $Microgametocyte$ divides,and the cytoplasm forms several long,flagellated structures called microgametes.
These microgametes then fertilize the $Macrogametocytes$ (female gametocytes) to form a zygote.

(D) The periodic appearance of malaria symptoms,known as paroxysm,is caused by the release of a toxic substance called haemozoin into the blood.
When the $Plasmodium$ parasite completes its erythrocytic cycle,the infected red blood cells rupture.
This rupture releases merozoites along with the toxic haemozoin and other metabolic waste products into the bloodstream.
The presence of these toxins triggers the immune system,leading to the characteristic chills and high fever associated with malaria.
Therefore,the periodic release of these substances into the blood corresponds to the periodic nature of the symptoms.

(B) The correct answer is $B$. The $Gametocyte$ stage of $Plasmodium$ is the infective stage for the female $Anopheles$ mosquito. When the mosquito bites an infected human,it ingests the gametocytes along with the blood. These gametocytes then undergo fertilization and development within the mosquito's gut,which provides the necessary environmental conditions for the parasite's life cycle to continue.

(D) The life cycle of $Plasmodium$ involves an exoerythrocytic phase in the liver.
After the initial infection,sporozoites enter liver cells to form cryptomerozoites (pre-erythrocytic schizogony).
Some of these cryptomerozoites re-enter fresh liver cells to undergo further asexual reproduction,resulting in the formation of metacryptomerozoites.
This secondary phase of development in the liver is known as exoerythrocytic schizogony.

(C) In the life cycle of $Plasmodium$,the gametocytes (male and female gametes) are formed within the human $R.B.Cs.$ during the erythrocytic schizogony cycle.
However,these gametocytes do not undergo further development or fertilization within the human body.
This is primarily due to the higher body temperature of humans $(37^{\circ}C)$,which is unsuitable for the further development of these gametocytes.
For the gametocytes to develop into gametes and undergo fertilization (syngamy),they require the lower temperature found in the gut of the female $Anopheles$ mosquito.

(B) The malarial parasite $(Plasmodium)$ undergoes schizogony in human red blood cells. When the schizonts rupture,they release merozoites and a toxic substance called haemozoin into the bloodstream. This release triggers the characteristic symptoms of malaria,specifically high fever accompanied by chills and rigors. Therefore,the concentration of parasites in the blood is highest and they are most easily detected when the patient experiences a sudden rise in temperature with rigors.

(A) Benign tertian malaria is caused by $Plasmodium \ vivax$.
In this type of malaria,the life cycle of the parasite in human red blood cells takes approximately $48$ hours to complete.
Upon the rupture of the infected red blood cells,a toxic substance called hemozoin is released,which is responsible for the characteristic chill and high fever that recurs every $48$ hours.

(C) In the life cycle of the malaria parasite $(Plasmodium)$,the shivering and high fever associated with malaria are caused by the release of a toxic substance called $hemozoin$.
This toxin is released into the bloodstream when the $R.B.Cs.$ (Red Blood Cells) rupture,releasing the $merozoites$ after the completion of the erythrocytic schizogony cycle.
Therefore,the correct answer is that shivering occurs when $merozoites$ are liberated from $R.B.Cs.$ along with the toxin.

(D) The organism likely to be destroyed is $Plasmodium$.
$Plasmodium$ is a protozoan parasite that requires a vector,specifically the female $Anopheles$ mosquito,to complete its life cycle.
The mosquito breeds in stagnant water bodies like ponds and puddles.
If these water bodies are destroyed,the breeding grounds of the mosquito are eliminated,which in turn disrupts the life cycle of $Plasmodium$,leading to its destruction.

(D) In the life cycle of the malarial parasite $(Plasmodium)$,the merozoites released from the liver cells enter the $RBCs$ (erythrocytes) of the human host.
Inside the $RBCs$,some merozoites differentiate into gametocytes (male microgametocytes and female macrogametocytes) instead of continuing the asexual erythrocytic cycle.
Therefore,gametocytes are formed from merozoites.

(B) The incubation period of malaria,which is the time between the infectious mosquito bite and the appearance of the first symptoms,typically ranges from $8$ to $10$ days. During this time,the $Plasmodium$ parasites multiply in the liver and subsequently infect the red blood cells.

(D) The zygote of $Plasmodium$ is formed in the gut of the female $Anopheles$ mosquito after fertilization.
This zygote is motile and elongated,and it is specifically known as an $ookinete$.
The $ookinete$ penetrates the gut wall of the mosquito to form an oocyst.

(C) The life cycle of $Plasmodium$ involves two hosts: humans and mosquitoes. In humans,the parasite undergoes asexual reproduction (schizogony) in two main stages:
$1$. Exo-erythrocytic cycle: This occurs in the liver cells,where the sporozoites transform into schizonts,which then rupture to release merozoites.
$2$. Erythrocytic cycle: The merozoites infect the $RBCs$ (red blood cells),where they again form schizonts,leading to the rupture of $RBCs$ and the release of more merozoites and toxins.
Therefore,the schizont stage is found in both liver cells and $RBCs$.

(C) The life cycle of the malaria parasite $(Plasmodium)$ begins when sporozoites are injected into the human bloodstream by an infected female $Anopheles$ mosquito.
These sporozoites first travel to the liver,where they undergo asexual reproduction (schizogony) within the liver cells (hepatocytes).
This phase is known as the pre-erythrocytic cycle or exo-erythrocytic cycle,which occurs before the parasite enters the red blood cells.
During this stage,the parasite consumes the cytoplasm of the liver cells,causing them to rupture and release merozoites into the blood,thereby harming the liver cells.

(C) $Phlebotomus$ $argentipes$,commonly known as the sandfly,acts as the biological vector for the protozoan parasite $Leishmania$ $donovani$.
This parasite is the causative agent of visceral leishmaniasis,also known as kala-azar or black fever.
The sandfly transmits the promastigote stage of the parasite to humans during its blood meal.

(B) The genus $Plasmodium$ (the causative agent of malaria) typically has a haploid chromosome number of $n = 14$. This means its diploid state $(2n)$ consists of $28$ chromosomes. Therefore,the correct option is $B$.

(B) The correct answer is $B$.
$Plasmodium$ $falciparum$ is responsible for causing malignant tertian malaria.
This type of malaria is also known as aestivo-autumnal,pernicious malaria,or black water fever.
It is considered the most dangerous form of malaria because it can lead to cerebral malaria,which is often fatal as it affects the brain.

(B) The correct answer is $B$.
Ronald Ross,a British scientist,in $1898$,demonstrated that the malarial parasite is transmitted by the $Anopheles$ mosquito.
He was awarded the Nobel Prize in $1902$ for this significant discovery.

(D) $Entamoeba$ $gingivalis$ is a commensal protozoan found in the human oral cavity, specifically in the gingival pockets and tartar of teeth.
It is primarily transmitted through direct contact, such as kissing, or through the sharing of contaminated utensils, food, or water (e.g., using the same bowl).
Therefore, both kissing and using the same bowl are modes of transmission for this organism.

(C) $Glossina \ palpalis$ (tse-tse fly) acts as a vector for the transmission of $Trypanosoma \ gambiense$.
$Trypanosoma \ gambiense$ is the causative agent of Gambian sleeping sickness,also known as Gambian fever.
Therefore,the correct option is $C$.

(A) The malarial parasite $(Plasmodium)$ undergoes asexual reproduction (schizogony) within the human red blood cells.
When the schizonts rupture,they release merozoites and toxic substances called hemozoin into the bloodstream,which triggers the characteristic chill and high fever (rigor).
Therefore,to observe the parasites in their active stages (such as ring stages or trophozoites) before they rupture the cells,blood samples should be collected approximately $1$ hour before the onset of the fever spike.

(A) Kala-azar (also known as visceral leishmaniasis) is caused by the protozoan parasite $Leishmania \ donovani$.
It is transmitted to humans through the bite of an infected female sand fly,specifically of the genus $Phlebotomus$.

(C) The Tse-tse fly ($Glossina$ $palpalis$) acts as a biological vector for the protozoan parasite $Trypanosoma$ $gambiense$.
This parasite is the causative agent of African sleeping sickness (African trypanosomiasis).
The fly transmits the infective stage of the parasite to humans through its bite.

(B) The correct answer is $B$.
$Plasmodium$ $malariae$ is the causative organism of quartan malaria.
This type of malaria is characterized by the recurrence of fever every fourth day.
This occurs because the duration of its erythrocytic cycle is $72$ hours.

(A) $Plasmodium \ vivax$ causes benign tertian malaria,which is characterized by the recurrence of fever every third day,i.e.,after $48$ hours.
This type of malaria is generally not fatal and is found worldwide,primarily in temperate regions.

(D) Quartan fever is a type of malaria caused by the parasite $Plasmodium$ $\text{malariae}$.
In this type of malaria, the fever cycle repeats every $72$ hours.
This occurs because the erythrocytic schizogony cycle of $Plasmodium$ $\text{malariae}$ takes approximately $72$ hours to complete, leading to the rupture of red blood cells and the release of pyrogens that trigger the fever spike.

(A) Schuffner's dots (or Schuffner's granules) are small,red,eosinophilic granules that appear in the cytoplasm of infected human red blood cells $(R.B.C.)$ during a malarial infection,specifically caused by $Plasmodium \ vivax$ or $Plasmodium \ ovale$.
These granules represent changes in the host cell membrane and cytoplasm due to the parasite's metabolic activity.
Therefore,they are associated with the $R.B.C.$ of man.

(B) 'Black water fever' is a severe and life-threatening complication associated with infection by $Plasmodium \ falciparum$.
It is characterized by massive hemolysis (destruction of red blood cells),which leads to hemoglobinuria (hemoglobin in the urine),causing the urine to appear dark or black.
$P. falciparum$ is also known for causing malignant tertian malaria or pernicious malaria,which can affect the brain (cerebral malaria) and is often fatal if not treated promptly.

(D) The malaria parasite,$Plasmodium$,requires two hosts to complete its life cycle.
$1$. The primary host (definitive host) is the female $Anopheles$ mosquito,where sexual reproduction occurs.
$2$. The secondary host (intermediate host) is the human,where asexual reproduction occurs.
However,in the context of transmission,the female $Anopheles$ mosquito acts as the vector. If the question asks for the host where the parasite undergoes sexual reproduction,it is the female $Anopheles$ mosquito. If it refers to the vector,it is also the female $Anopheles$ mosquito. Given the standard options provided,$D$ is the correct answer as the female $Anopheles$ mosquito is the definitive host.

(C) Enteritis refers to the inflammation of the small intestine. In the context of common water-borne and food-borne diseases in India, it is frequently caused by the protozoan parasite $Entamoeba$ $\text{histolytica}$, which causes amoebiasis.
This infection occurs primarily through the fecal-oral route, which involves the ingestion of cysts of the parasite present in contaminated food and water.
Therefore, the correct mode of transmission is the ingestion of cysts with food and drinks.

(A) Kala-azar,also known as visceral leishmaniasis,is a disease caused by the protozoan parasite $Leishmania$ $donovani$.
This parasite is transmitted to humans through the bite of an infected female sand fly,which belongs to the genus $Phlebotomus$.
Therefore,the causative agent is $Leishmania$ and the vector (transmitter) is $Phlebotomus$.

(C) Sleeping sickness, also known as African trypanosomiasis, is a parasitic disease caused by the protozoan $Trypanosoma$ $brucei$.
This parasite is transmitted to humans through the bite of an infected $Tse-tse$ $fly$ (genus $Glossina$).
Therefore, the $Tse-tse$ $fly$ acts as the biological vector for this disease.

(B) An endemic disease is one that is constantly maintained at a baseline level in a geographic area without external inputs.
Among the given options, $Amoebiasis$ (caused by $Entamoeba histolytica$) is considered endemic in many tropical and subtropical regions, including parts of India, due to poor sanitation and contaminated water supplies.
Common cold, influenza, and hepatitis often occur as epidemics or sporadic outbreaks rather than being strictly classified as endemic in the same context as $Amoebiasis$.