Kala-azar, also known as visceral leishmaniasis, is transmitted by (c) Anopheles fly. This disease is caused by the protozoan parasite Leishmania donovani, primarily transmitted to humans through the bite of infected female sandflies of the genus Phlebotomus (Old World) or Lutzomyia (New World). These sandflies typically thrive in rural areas with poor sanitation and are most active during dusk and dawn. When an infected sandfly bites a human, it injects the parasite into the bloodstream, leading to the development of kala-azar. Effective control measures, such as vector control and treatment of infected individuals, are essential to prevent the spread of this disease.

Malaria parasites that cause deadly malaria are (b) Plasmodium falciparum. This species is responsible for the majority of severe malaria cases and deaths globally, making it the deadliest of the malaria parasites. Plasmodium falciparum can lead to severe complications such as cerebral malaria, organ failure, and death, particularly in young children and pregnant women. While other species like Plasmodium vivax (c) and Plasmodium malariae (a) can cause malaria, they typically result in milder forms of the disease. Plasmodium ovale (d) is another species but is less common and usually causes less severe symptoms compared to P. falciparum.

Malaria being spread by female Anopheles mosquitoes was first discovered by (b) Ronald Ross. Ross, a British medical doctor, made this groundbreaking discovery in 1897 while working in India. Through his meticulous experiments, Ross demonstrated the link between Anopheles mosquitoes and malaria transmission. His discovery paved the way for understanding the complex lifecycle of the malaria parasite and revolutionized approaches to malaria control. Ronald Ross’s work earned him the Nobel Prize in Physiology or Medicine in 1902, making him the first British Nobel laureate in medicine. His contributions have had a profound impact on global efforts to combat malaria.

The BCG vaccine is typically given to newborns, so the correct answer is (c) Newborn. It is administered shortly after birth, usually within the first few days to weeks of life. This timing is optimal for providing protection against tuberculosis (TB) in infancy, as newborns are at increased risk of severe forms of TB if exposed to the bacterium. The BCG vaccine helps prevent severe forms of TB, such as TB meningitis and miliary TB, in young children. In some countries, the BCG vaccine may also be given to older children and adults at high risk of TB infection or complications.

Plague primarily spreads through (a) Bacteria. It is caused by the bacterium Yersinia pestis. Transmission occurs through the bite of infected fleas, primarily from rodents like rats, squirrels, and prairie dogs. Additionally, handling infected animals or inhaling respiratory droplets from infected individuals, particularly in cases of pneumonic plague, can also lead to transmission. Plague is not caused by protozoa (b) or viruses (c). While certain diseases caused by protozoa or viruses can spread similarly through vectors or respiratory droplets, plague specifically involves the bacterium Yersinia pestis as its causative agent.