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Malaria would have been a simple problem if not for its habit of
recurring again and again and again. I have seen patients who have had malarial attacks
35-40 times in 3-4 years period. It is this problem which also keeps the disease alive in
a community and makes its control quite difficult.
Why does malaria recur?
Following are the reasons for recurrence
of malarial attacks:
1. Absence of effective immune
response: Immune response against malarial infection is very poor and it does not
protect against re-infections. Acquired immunity develops after several attacks of malaria
over several years. This immunity is stage specific, species specific and 'strain'
specific. It does not have any sterilizing effect on the parasitemia and immune adults are
still re-infected. However, the clinical signs and symptoms are reduced with development
of clinical immunity.
Various explanations have been offered
for these observations. Generalised immunosuppression by the parasite; presence of T-cell
independent antigens which fail to induce immune response; inhibition of B-cell
proliferation; and extreme polymorphism or clonal variation of immunologically relevant
antigens could be the causes for the poor immune response in malaria.
2. Exposure to repeated mosquito bites
and re-infection: The commonest cause for recurrence of malaria is re-infection. The
patient is exposed to fresh mosquito bites soon after completing the anti malarial
treatment. On the one hand he has no immunity from the past infection and on the other,
the antimalarials do not prevent establishment of the fresh infection. Therefore, unless
the patient observes stringent anti mosquito measures, re-infection is inevitable in an
endemic area.
3. Incomplete treatment: All blood
schizonticidal drugs suppress the erythrocytic schizogony and give symptomatic relief. The
patient may stop the drugs due to various reasons like vomiting, ignorance and financial
constraints. This results in recrudescence within a short period. Also, if the patient
does not take the complete course of primaquine, relapses can occur from re-activation of
hypnozoites in the liver.
Proper patient education regarding the
complete course of anti malarials is very important.
4. Relapse: In cases of P.
vivax and P. ovale infections, recurrent attacks could be due to
re-activation of hypnozoites in the liver. This can occur any time after 30-180 days of
the primary attack. The relapses have the characteristic symptoms of malaria. Splenomegaly
may be a prominent feature in these patients.
Such long-term relapses commonly occur in
patients who have either not taken primaquine or taken incomplete treatment.
5. Recrudescence:
In P. falciparum and P. malariae infections, the parasites can remain in
the blood for months or even years and cause recurrent symptoms from time to time. In
falciparum malaria, such recrudescence can occur within 28 days of the primary attack and
may indicate partial resistance to chloroquine. However, treating every case of recurrent P.
falciparum as resistant malaria is unjustified. One should consider the possibility
of re-infection in most of these cases. Orht et al have studied the recrudescent isolates
by PCR genotyping and have concluded that PCR genotyping could be a practical method of
distinguishing recrudescence from re-infection.
It is a common observation
that in a household, only some members get recurrent attacks of malaria while the others
escape the infection. In such cases, it is important to find the cause for this
phenomenon. The person may be getting bitten by the mosquitoes elsewhere, may be at
his/her workplace. The resting and sleeping habits of such individual may be facilitating
mosquito bites. Or else, any of the causes listed above may also be playing a role.
Clinical approach
to cases of recurrent malaria
Table below shows the
causes for recurrence of malaria at different intervals
Recurrence |
Within 8-10 days |
After 2 weeks |
After 2 months |
1st possibility |
?P. falciparum |
?Re-infection |
?Re-infection |
2nd possibility |
?Compliance |
?P. falciparum |
?Relapse |
Interpretation of
repeat MP test reports in cases of recurrent malaria
| Recurrence interval |
Initial infection |
Repeat MP Test |
Interpretation |
Treatment |
Within 8-10 days of initial attack |
P. vivax |
Same,
P. vivax |
Incomplete
or inadequate treatment; poor compliance; vomiting |
Re-treat
with chloroquine + Primaquine |
| P. falciparum |
? drug
resistant infection |
Treat with
second line drugs + Primaquine |
| P. falciparum |
Rings of P. falciparum |
? Drug
resistant P. falciparum |
Treat with
second line drugs + Primaquine |
Recurrence between
2 weeks and
2 months |
P. vivax |
Same,
P. vivax |
?
Re-infection |
Re-treat |
| P. vivax/mixed |
Only rings of P. falciparum |
Most
likely a re-infection; persisting P. falciparum infection will generally show
gametocytemia by 8-10 days. |
Re-treat |
| P. vivax/mixed |
Rings and gametocytes of P. falciparum |
Could be a
re-infection; consider a possibility of recrudescence of chloroquine resistant P.
falciparum |
Consider
second line drugs |
| P. falciparum |
P. vivax/mixed |
Re-infection |
Re-treat |
| P. falciparum |
Only rings of P. falciparum |
Likely to
be re-infection |
Re-treat |
| P. falciparum |
Rings and gametocytes of P. falciparum |
Most
likely re-infection; also consider recrudescence |
Re-treat;
consider second line drugs |
Recurrence after
2 months |
P. vivax/mixed |
P. vivax |
Re-infection
or relapse; larger spleen may indicate relapse |
Re-treat;
ensure 14 days of Primaquine |
| P. falciparum |
Any type |
Re-infection |
Re-treat;
advise on mosquito control |
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