Toxoids, antigen-based and other vaccine preparations

Toxoids, antigen-based and other vaccine preparations 

Diphtheria and tetanus vaeeine are two eommonly used toxoid-based vaccine preparations. The initial stages of diphtheria vaccine production entails the growth of Corynebacterium diphtheriae. The toxoid is then prepared by treating the active toxin produced with formaldehyde. The product is normally sold as a sterile aqueous preparation. Tetanus vaccine production follows a similar approach Clostridium tetani is cultured in appropriate media, the toxin is recovered and inactivated by formaldehyde treatment. Again, it is usually marketed as a sterile aqueous-based product. 

All of the vaccine preparations discussed thus far are bacterial or viral-based. Typhus vaccine, on the other hand, targets a parasitic disease. Typhus (spotted fever) refers to a group of infections caused by Rickettsia (small, non-motile parasites). The disease is characterized by severe rash and headache, high fever and delirium. The most common form is that of epidemic typhus ( classical or louse-borne typhus). This is associated particularly with crowded, unsanitary conditions. 

Without appropriate antibiotic treatment, fatality rates can approach 100%. The causative agent of epidemic typhus is Rickettsia prowazekii. Typhus vaccine consists of a sterile aqueous suspension of killed R. prowazekii which has been propagated in either yolk sacs of embryonated eggs, rodent lungs or the peritoneal cavity of gerbils. 

To date, no effective vaccine has been developed for many parasites, notably the malaria-causing parasitic protozoa Plasmodium. One of the major difficulties in such instances is that parasites go through a complex life cycle, often spanning at least two different hosts. 

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