CLINICAL & BASIC RESEARCH

SQU Med J, August 2011, Vol. 11, Iss. 3, pp. 377-382, Epub. 15th Aug 11
Submitted 15th Jan 11
Revision ReQ. 4th May 11, Revision recd. 28th May 11
Accepted 4th Jun 11

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
200810


 60
 51.7% 35%
 16.7% 5%
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 66.6% 36.8%
 28% 2%



 –:مفتاح الكلمات

aBstract: Objectives: This study aimed to compare the clinical presentations and complications in patients having 
mixed malaria infection of Plasmodium falciparum and Plasmodium vivax with those of patients with malaria 
due to a P. falciparum mono-infection. Methods: The medical records of malaria patients admitted to Kasturba 
Medical College, Manipal, India, during the years 2008–10 were analysed. Inclusion criteria were patients in whom 
P. falciparum and P. vivax coinfection or P. falciparum mono-infection alone was confirmed on peripheral smear 
examination. Exclusion criteria were patients in whom P. vivax infection alone was diagnosed on peripheral smear 
examination. The sample size was twenty patients diagnosed with mixed infection of P. falciparum and P. vivax and 
60 patients diagnosed with P. falciparum mono-infection. Results: 35% of mixed infections had thrombocytopenia 
as compared to 51.7% of P. falciparum mono-infections. A total of 5% of the mixed infections had renal failure 
as compared to 16.7% of the falciparum mono-infections. Total bilirubin was raised in 15.8% of mixed infections 
and in 46.6% of falciparum mono-infections. Abnormal liver enzymes were seen in 36.8% of mixed infections and 
in 66.6% of falciparum mono-infections. None of the mixed infections had a parasite index over 2% while it was 
present in 28% of the falciparum mono-infections. Conclusion: Patients with mixed infections were found to have 
a lower incidence of severe complications such as anaemia, thrombocytopenia, liver and renal dysfunction and 
a lower parasite index. Thus mixed malaria tends to have a more benign course as compared to malaria due to 
P. falciparum mono-infection.

Keywords: Malaria, Falciparum; Epidemiology; Parasitology; Vivax; Host-Parasite interactions; India

Comparison of the Clinical Profile and
Complications of Mixed Malarial Infections 

of Plasmodium Falciparum and Plasmodium 
Vivax versus Plasmodium Falciparum 

Mono-infection
*Vivek Joseph,1 Muralidhar Varma,2 Sudha Vidhyasagar,2 Alvin Mathew1 

CLINICAL & BASIC RESEARCH

1Medical Students and 2Department of Medicine, Kasturba Medical College, Manipal, Karnataka, India.
*Corresponding Author email: vivek101@gmail.com



Comparison of the Clinical Profile andComplications of Mixed Malarial Infections of Plasmodium Falciparum and Plasmodium Vivax 
versus Plasmodium Falciparum Mono-infection

378 | SQU Medical Journal, August 2011, Volume 11, Issue 3

Malaria is a tropical disease caused by the protozoan parasite Plasmodium. It is one of leading causes of morbidity 
and mortality in the tropics affecting around  
190–311 million people worldwide and killing 7–10 
million people every year.1 The disease in humans 
is caused by the direct effects of red blood cell 
(RBC) invasion and destruction by the parasite 
and the host’s response. Splenic, immunologic and 
filtrative clearance is augmented and the removal 
of both parasitised and uninfected erythrocytes 
is accelerated. Parasitised cells escaping splenic 
removal are destroyed when the schizont ruptures; 
this in turn induces activation of macrophages and 
cytokines which cause fever and other pathological 
effects. The complications seen in malaria include 
severe anaemia, hypoglycaemia, coma, convulsions, 
renal failure, bleeding and shock.2 

Malaria in humans is caused by Plasmodium 
falciparum, P. vivax, P. ovale, P. malariae and 
the predominantly simian parasite P. knowlesi.3  
Of these, falciparum and vivax are the two most 
common infecting species. P. falciparum causes 
the most severe disease and almost all the fatalities, 
whereas P. vivax, although usually considered to 
be benign, causes repeated debilitating relapses, 
sometimes life-threatening complications, and 
intrauterine growth retardation. As several 
Plasmodium species may be present in a particular 
area, infections with more than one species of 
Plasmodium transmitted by the same vector at 
the same time are to be expected. Malaria is not 
unique in this regard, mixed infections with Lyme 
disease, human granulocytic ehrlichiosis and 
babesiosis, transmitted by Ixodes ticks occur in 
the Northeastern USA,4 and positive associations 
between geohelminths are common globally.5 
However, there are only sporadic reports on mixed 
malarial infections. This can be attributed to the 
fact that mixed infections are often difficult to 
diagnose on routine smear examination. This is 
due to a combination of observer error, difficulty 

in distinguishing between the ring forms of the 
various Plasmodium species, the undetectable 
presence of P. vivax and P. ovale liver hypnozoites, 
and low density infection below the threshold of 
detection by microscopy (<1 X 108 parasites in an 
adult). The relevance of interactions between the 
different Plasmodium species extends beyond mere 
academic curiosity.6,7 Studies report variable and 
sometimes even contradicting results on the effect 
of interactions in mixed malarial infections;8‒10 

therefore, we undertook this study to compare the 
clinical presentations and complications of mixed 
malarial infections of P. falciparum and P. vivax to 
those of malaria due to P. falciparum alone.

Methods
This retrospective observational study included all 
the malaria patients who were admitted to Kasturba 
Medical College, a tertiary teaching hospital in 
Karnataka, South India, during the period June 2008 
to July 2010. Malaria is an endemic disease in this 
part of India. There are 150–200 annual reported 
cases of malaria in our College. The majority of the 
complicated cases are due to P. falciparum infection. 
The patients included in the study were all over 18 
years of age and presented to the hospital on their 
own initiative with various complaints such as 
fever and were subsequently admitted. Only those 
in whom malaria was confirmed on peripheral 
smear examination were included in the study. 
On the basis of peripheral smear examination two 
groups were formed. Patients who showed both P. 
falciparum and P. vivax on their peripheral smear 
were allocated to Group 1, while those who showed 
only P. falciparum on peripheral smear examination 
were allocated to Group 2. Those patients who 
showed only P. vivax on the peripheral smear were 
excluded from the study. Due to the small number 
of mixed malaria cases (n = 20) it was decided to 
select all the patients from Group 1 (mixed infection 
of P. falciparum and P. vivax) for the study. Patients in 

Advances in Knowledge
1. The literature on the clinical outcome on mixed malarial infections is scanty. It is intuitive to think that mixed infections will add to 

morbidity, but our study in fact shows an improvement in the outcome.

Application to patient care
1. Our study throws light on the potential dangers of treatment and preventive measures that selectively suppress the less virulent 

Plasmodium vivax infection. This can have important clinical implications.



Vivek Joseph, Muralidhar Varma, Sudha Vidhyasagar, Alvin Mathew

Clinical and Basic Research | 379

Group 2 (P. falciparum mono-infection) who were 
age and sex matched to each of the 20 cases of 
mixed malarial infection were taken for the study. 
The total number of P. falciparum mono-infections 
selected was 60, thus giving a ratio of 1:3 (i.e. three 
P. falciparum mono-infections for every mixed 
malarial infection). Prior to the start of the study the 
following terms were defined. Anaemia was defined 
as haemoglobin less than 10g/dl; thrombocytopenia 
as platelets less than 100,000; raised bilirubin as total 
bilirubin greater than 2 g/dl; raised liver enzymes as 
serum aspartate transferase (AST)/ serum alanine 
transferase (ALT) greater than 4 times normal 
range; serum creatinine was defined as raised when 
serum levels were greater than 1.6 g/dl. The parasite 

index was defined as the number of infected RBCs 
seen on peripheral smear examination per 1,000 
RBCs expressed in percentage. 

The research was undertaken in the period 
March to December 2010. Prior approvals from 
the Ethical Committee of Kasturba Medical College 
and from the Superintendent of the Medical 
Records Department at Kasturba Medical College 
were taken before commencement of the study. All 
the relevant patient records were collected from the 
Medical Records Department and analysed. The 
data of the two groups were compared using the 
chi square test for each study parameter using the 
Statistical Package for the Social Sciences (SPSS, 
IBM, USA, Version 18). 

Table 1: Comparison of the incidence of the various study parameters among mixed malarial infection of P. falciparum 
and P. vivax to that of P. falciparum mono-infection along with their P values

Parameter Mixed Infections of P. falciparum 
and P. vivax

                   P. falciparum mono-infection P value

Number Percentage Number Percentage

Anaemia 3 15 17 28.3 0.233

Splenomegaly 6 30 42 70 0.0015

Thrombocytopenia 7 35 31 51.4 0.196

Raised bilirubin 3 15.8 28 46.6 0.0118

Raised liver enzymes 7 36.6 32 66.6 0.155

Serum creatinine 1 5 10 16.7 0.189

Parasite index >2% 0 0 16 28 0.009

0%

15%

28.30%
30%

70%

35%

36.60%

5%

28%

16.70%

0%

66.60%

15.80%

46.60%

51.40%

10%

20%

30%

40%

50%

60%

70%

80%

Ana
em

ia

Spl
eno

me
galy

Thr
om

boc
ytop

enia

Rai
sed

 Bil
iubi

n

Rai
sed

 Liv
er E

nzy
me

s

Ser
um

n C
rea

tine

Par
asit

e in
dex

 >2
%

Mixed infection P Falciparum mono-infection

Figure 1: The incidence of complications in mixed malarial infection of P. falciparum and P. vivax compared to that of P. 
falcipaum mono-infection.



Comparison of the Clinical Profile andComplications of Mixed Malarial Infections of Plasmodium Falciparum and Plasmodium Vivax 
versus Plasmodium Falciparum Mono-infection

380 | SQU Medical Journal, August 2011, Volume 11, Issue 3

Results
The study consisted of data on 80 subjects collected 
over a period of 2 years. It consisted of 20 cases 
of mixed malarial infection of P. falciparum and P. 
vivax and 60 cases of P. falciparum mono-infection. 
The cases of mixed infections consisted of 14 
males (70%) and 6 females (30%). The P. falciparum 
mono-infection consisted of 45 males (75%) and 15 
females (25%). The mean age of both the groups was 
35 years. All patients in both the groups recovered 
from the disease. 

Table 1 shows a comparison of the results for 
each parameter along with their P values. Figure 
1 gives a pictorial representation comparing the 
incidence of complications in mixed malarial 
infection of P. falciparum and P. vivax to that of P. 
falciparum mono-infection. Patients with mixed 
malarial infections of P. falciparum and P. vivax were 
found to have a lower incidence of all the study 
parameters as compared to P. falciparum mono-
infection. For example splenomegaly was found in 
30% of mixed malaria infections as compared to 
70% of P. falciparum mono-infections. Similarly only 
35% of mixed infections had thrombocytopenia 
as compared to 51.7% of P. falciparum mono-
infections. Raised serum creatinine was seen in 
5% of the mixed infections as compared to 16.7% 
of the falciparum mono-infections. Total bilirubin 
was raised in only 15.8% of mixed infections while it 
was raised in 46.6% of falciparum mono-infections. 
A parasite index of more than 2% was not seen in 
any mixed infections but it was seen in 28% of P. 
falciparum mono-infections.

Discussion
Mixed-malarial (falciparum and vivax) infections 
very often go unrecognised, or are underestimated. 
In our study, only 20 patients (2.9%) with mixed 
malaria infection, on peripheral smear examination, 
were identified out of a total of 689 cases admitted 
to Kasturba Medical College as malaria cases during 
the study period of 2 years. This is consistent with 
surveys done in Thailand, which report that mixed 
infections constitute less than 2% of all malaria 
cases. However, studies using sensitive polymerase 
chain reaction (PCR) methods in the same 
region as the survey put the incidence of mixed 
infections at around 30% of all malarial infections.11 

Thus mixed malarial infections are often under  
estimated and can have a significant impact on 
patient management.   

In our study anaemia was seen only in 15% 
of mixed malarial infections of P. falciparum and  
P. vivax as compared to 36.6% of P. falciparum mono-
infections. These findings correlated with studies 
conducted in Thailand where they found that 
likelihood of developing anaemia was 1.8 times 
less in mixed malaria as compared to falciparum 
malaria.12 Similarly, in our study, 30% of patients 
with mixed malaria infections had splenomegaly 
as compared to 70% of patients with P. falciparum 
mono-infection. Thus splenomegaly is significantly 
(P = 0.0015) more common in P. falciparum mono-
infection as compared to mixed malarial infection. 
A study done in Punjab, India, found that the 
presence of splenomegaly is three times more 
common in P. falciparum infection compared to 
other forms of malaria.13 Thrombocytopenia, one 
of the severe complications of malaria is attributed 
to reduced platelet life span and splenic pooling.14,15 
Macrophage activation and hyperplasia, especially 
in the spleen, may also play a role. Our study 
noted that thrombocytopenia was more common 
in falciparum mono-infections as compared to 
mixed infections of both falciparum and vivax. 
Thrombocytopenia was seen in 51% of falciparum 
malaria cases as compared to 35% of mixed malarial 
infections; however, this finding is not statistically 
significant. It is interesting to notes that a study 
done in Kuwait showed a higher prevalence of 
thrombocytopenia in mixed and P. vivax mono-
infections infections.8  

Our study showed a higher incidence of renal 
failure in patients with falciparum mono-infection 
(17%) as compared to mixed malarial infections 
(5%). Studies have shown that there is a lower 
incidence and better prognosis for renal failure in 
patients with vivax malaria;16 however, no similar 
studies on renal failure in patients with mixed 
malarial infection have been seen. The precise 
mechanism of renal failure in malaria is not clearly 
known. Cytoadherence of P. falciparum infected 
red blood cells to the vascular endothelial cells of 
different host organs along with rosette formation 
is considered as the most important mechanism of 
severe malaria.16,17 Another complication of malaria 
is liver dysfunction which, when accompanied 
by other vital organ dysfunction (often renal 



Vivek Joseph, Muralidhar Varma, Sudha Vidhyasagar, Alvin Mathew

Clinical and Basic Research | 381

impairment), often carries a poor prognosis. 
Hepatic dysfunction contributes to the severe 
complications of malaria such as hypoglycaemia, 
lactic acidosis, and impaired drug metabolism.2 
In our study, it was seen that the signs of liver 
failure such as raised bilirubin levels and deranged 
liver enzymes were seen more commonly in P. 
falciparum mono-infection as compared to mixed 
infections of P. falciparum and P. vivax. The P value 
for the association of raised bilirubin with mixed 
and falciparum mono-infections was found to be 
significant (P = 0.0118) while the P value for raised 
liver function tests was not found to be significant 
(P = 0.155). Mixed infections of P. falciparum and P. 
vivax were associated a with statistically significant 
(P = 0.009) lower parasite index as compared to 
P. falciparum mono-infection. None of the mixed 
infections had a parasite index of more than 2%, 
while 28% of cases in falciparum mono-infection 
had a parasite index of more than 2%. Similar studies 
done in Tanzania arrived at the same findings.18

Immunity to malaria in humans is poorly 
understood, but it is thought to be both species 
and genotype specific. Our study suggests that a 
coinfection of P. vivax protects against the severe 
complications of P. falciparum; however, this 
protective phenomenon of mixed malaria has 
proved to be controversial, as some workers have 
suggested that mixed infections are beneficial, 
whereas others have suggested that they are 
detrimental to the host. For example, in the 
1930s, the classical clinical studies of human 
malariotherapy for neurosyphilis demonstrated that 
P. falciparum suppressed P. vivax parasitaemia when 
both species were inoculated simultaneously.19 In 
another more recent study done in Thailand, it was 
seen that naturally acquired mixed infections with 
other less severe malaria species appear to attenuate 
the severity of P. falciparum infection.20 On the Thai-
Burmese border, pregnant women whose first 
attack of malaria during pregnancy was caused by 
P. vivax had a significantly lower risk of developing 
P. falciparum later in the pregnancy.9 However, there 
are also several conflicting reports in the literature; 
for example, Gopinathan and Subramanian’s 
study in 1986 found that mixed infections with P. 
falciparum and P. vivax were associated with an 
increased incidence of complications like cerebral 
malaria.10 

A major limiting factor in our study was the 

very small sample size of only 20 mixed malarial 
infections of P. falciparum and P. vivax over a period 
of 2 years. However, as mentioned earlier, we 
believe that mixed malarial infections are very 
often underestimated and only by using newer, 
more sensitive investigations such as PCR can 
we determine the true extent of mixed malarial 
infections. If further studies confirm our hypothesis 
that P. vivax co-infection indeed has a beneficial 
disease-modifying effect on the more severe P. 
falciparum infection, it would then be legitimate 
to speculate whether therapeutic suppression of 
the more benign P. vivax species in the population 
would cause P. falciparum malaria to become an even 
more serious public health problem. This scenario 
may explain why there is an increase in mortality 
resulting from the continued use of chloroquine as a 
first line treatment in Africa in the face of mounting 
resistance to this drug by P. falciparum, but not by 
the other parasite species.6,7 Thus we believe that we 
have to ask ourselves whether two mosquito bites 
are better than one.

Conclusion
In this study, it was seen that patients with mixed 
malarial infections of P. falciparum and P. vivax 
were found to have a lower incidence of severe 
complications such as anaemia, thrombocytopenia, 
liver failure and renal failure that are often associated 
with P. falciparum mono-infections. It was also seen 
that mixed malarial infections had a lower parasite 
index as compared to P. falciparum mono-infections. 
From the above findings, we conclude that the P. 
vivax infection has a beneficial disease modifying 
effect on the more severe P. falciparum malaria. 
We believe that further studies are required to 
fully address this complex, but often understudied 
aspect of malaria.

c o n f l i c t o f i n t e r e s t
The authors reported no conflict of interest.

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