Use of PCR for detection of subpatent infections of lizard malaria: implications for epizootiology

Abstract

The estimated prevalence of a malaria parasite, Plasmodium mexicanum, of western fence lizards, Sceloporus occidentalis, was compared using two techniques: microscopic examination of blood smears, and nested PCR amplification of the 18S small subunit rRNA gene. Two sites in northern California, USA were investigated, one with known long‐term high prevalence of the parasite (30% by blood smear scanning), and one with low prevalence (6%). The nested PCR readily detected very low‐level infections (< 1 parasite per 10 000 erythrocytes); such infections are often subpatent by normal microscopic examination. False negatives (scored as not infected after scanning the blood smear, but found infected via PCR) were rare at both sites (4% at the high‐prevalence site, 6% at the low‐prevalence site). However, a greater proportion of infections was detected only by PCR at the low‐prevalence site (50% vs. 9%). If 50% of the infections sustain very weak parasitaemia where lizards are rarely infected, this would accord with hypotheses that predict that parasites should reduce infection growth when transmission is uncommon. The study demonstrates that PCR is a powerful tool to detect very low‐level malarial infections in vertebrate hosts, including those with nucleated erythrocytes.

Occurrence of blood parasites and intensity of infection in Prunella modularis in the montane and subalpine zone in the Slovak Carpathians

“…Perkins et al 1998, Bensch et al 2000, Jarvi et al 2002, Križanauskienė et al 2006 (Dymowska and Żukowski 1968) and H. orizivorae (Peirce and Mead 1976), our findings are not morphologically identical with any of these species. Haemoproteus sp.…”

“…PCR analysis proved to be more sensitive in detecting blood parasites (e.g. Perkins et al 1998, Bensch et al 2000, Jarvi et al 2002, Križanauskienė et al 2006. Especially at early stages of infections parasites can be overlooked in blood smears (Jarvi et al 2003).…”

Avian Hemosporidian Parasites From Northern California Oak Woodland and Chaparral Habitats

“…Fully 39% of sampled birds were infected with parasites of one or more of the studied genera, with a total of 16 species of parasite. However, examination of single blood smears taken from individual birds presents an underestimate of true prevalence because some infections of these parasites remain at low levels in the blood, and are subpatent upon examination of microscope smears; this is demonstrated by using sensitive molecular assays, such as polymerase chain reaction (PCR) (Perkins et al, 1998). The recent development of molecular techniques to separate subpatent infections using genus-specific restriction enzymes may improve estimates of prevBirds family, common name, taxonomy n H .…”

Life history of a malaria parasite (Plasmodium mexicanum): independent traits and basis for variation

“…The recipients were collected from sites where malaria has been absent in the lizards over the past 20 years (Schall & Marghoob 1995). Examination of blood smears from these animals con¢rmed they were not already infected (extremely weak infections which are not detectable by such microscopic examination are rare at the HREC) (Perkins et al 1998). Asexual parasitaemia was determined in the donor infections by counting 1000 RBCs at £1000 magni¢cation (Giemsa-stained thin blood smears) (Schall & Bromwich 1994).…”