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It is certainly a one-sided opinion—even though generally adopted at the moment—that all infectious agents which are still unknown must be bacteria. Why should not other microorganisms just as well be able to exist as parasites in the body of animals?


Almost any infection, especially if subacute or insidious in its onset, can be baffling and can belong to the ‘fever of undetermined origin’ group of infections. Syphilis and tuberculosis were the great mimics of the past. Now malaria and Epstein–Barr mononucleosis (EBM) can be regarded as important mimics. EBM (Epstein–Barr mononucleosis, infectious mononucleosis, glandular fever) can be a perennial baffler and can be confused with HIV infection in its primary clinical phase. Any of the febrile diseases can be confusing before declaring themselves with classic symptoms such as the jaundice of hepatitis or the rash of dengue fever, or before serological tests become positive.

Viral and protozoal infections that can present as masquerades include:

  • HIV infection (especially primary)

  • EBV

  • TORCH organisms: toxoplasmosis, rubella, CMV, HSV

  • hepatitis A, B, C, D, E

  • mosquito-borne infections: malaria, dengue fever, yellow fever/other haemorrhagic fevers, Japanese encephalitis, Ross River fever, West Nile fever

The TORCH organisms (TORCH being an acronym for toxoplasmosis, rubella, CMV and herpes) are well known for their adverse intra-uterine effects on the fetus. Three are viral (toxoplasmosis is a protozoan) and the first three of these fetal pathogens are acquired by passage across the placenta. Most of these organisms are noted for being opportunistic infections in immunocompromised patients, especially in later stage HIV infection.

The mosquito-borne infections causing encephalitis and haemorrhagic fevers are mainly viral, apart from the protozoan causing malaria, and are of particular significance in travellers returning from endemic areas (refer to CHAPTER 15).

The major protozoal diseases of humans are:

  • blood: malaria, trypanosomiasis

  • GIT: giardiasis, amoebiasis, cryptosporidium

  • tissues: toxoplasmosis, leishmaniasis, babesiosis

Most of the world’s serious protozoal infections—malaria, African trypanosomiasis, leishmaniasis, amoebiasis—occur in tropical areas and are listed and explained in CHAPTER 15.


Four infections—EBV, primary HIV, CMV and toxoplasmosis—produce almost identical clinical presentations and tend to be diagnosed as glandular fever or pseudoglandular fever. It is important for the first contact practitioner to consider all four possibilities, especially keeping in mind the possibility of HIV infection.

A worthwhile approach is to make a provisional diagnosis based on the clinical variations as presented in TABLE 28.1.

Table 28.1Clinical features differentiating HIV, EBV, CMV and toxoplasmosis infections (all can present with a similar illness)

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