In order to cause a disease, a pathogen must be able to:
· travel from one host to another
· get into the host tissues
· cause damage to the hosts tissues
Pathogenic organisms can be transmitted in a variety of ways. Once it reaches a new host, the pathogen will need to pass through the primary defences that the host has to prevent entry. Once inside the host, the pathogen must overcome any secondary defences or immune responses. Most pathogenic organisms are well adapted to overcoming these obstacles.
The most commons forms of transmission are:
· by means of a vector
· by physical contact
· by droplet infection
Transmission of malaria:
Malaria is caused by a eukaryotic organism from the genus Plasmodium. There are a number of different species. Plasmodium falciparum is the most widespread, but P. vivax, P. ovale, and P. malariae also caused malaria.
Malaria is spread by a vector. The female Anopheles mosquito carries the Plasmodium from an infected person to an uninfected person. Female Anopheles mosquitoes feed on blood. They have mouthparts that are adapted as a fine tube or proboscis. This is used to penetrate a blood vessel and withdraw blood. Malarial parasites live in the red blood cells of the human host and feed on the haemoglobin.
The parasites are transmitted in the following cycle:
· If the host already has malaria, the mosquito will **** the parasite gametes into its stomach.
· The gametes fuse and the zygotes develop in the mosquito’s stomach.
· Infective stages are formed and these move to the Mosquitoes salivary glands.
· When the mosquito bites another person, it injects a little saliva as an anticoagulant.
· This saliva contains the infective stage of the parasite.
· In the human host, the infective stages enter the livers where they multiply before passing into the human blood again.