Page 122 - parasitology for medical and clinical laboratoryprofessionals

102 CHAPTER 4

fatal inflammation of the brain called encephalitis. In this
Source: Centers for Disease Control and Prevention (CDC) tions are merely nuisances, and may include dizziness,
case, fever is followed by headache and confusion, then
stupor, and ensuing coma caused when massive numbers
of larvae and parasites die. Other common drug reac-

weakness, and nausea.
For medications that cause the wholesale death of
the parasites, symptoms may include fever, headache,
muscle pain, abdominal pain, nausea and vomiting,
weakness, dizziness, lethargy, and even asthma. Reac-
tions usually begin within two days of starting treatment
and may last between two and four days. No treatment
can reverse elephantiasis and surgery may be required to
FIGURE 4-19 Microfilarial pathogen Onchocerca
remove surplus tissue and to provide a way to drain the
volvulus in its larval form, causative agent for river fluid from the damaged lymphatic system. Surgery may
blindness
also be used to ease massive enlargement of the scrotum.
Elephantiasis of the legs may also be aided by elevating
diagnosis may be difficult because, in the first stages, the the legs to lower the circulation of blood to the lower
disease mimics other bacterial skin infections. To make limbs and by providing support with elastic bandages.
an accurate diagnosis, the physician looks for a pattern The prognosis for patients in the early stages or in mild
of inflammation and signs of lymphatic obstruction, to- cases is quite good, especially if the victim can avoid re-
gether with the patient’s possible exposure in an area infection. The disease is rarely fatal, and with continued
where filariasis is common. The larvae (microfilariae) can WHO medical intervention, with a goal of eliminating
also be found in the blood, but mosquitoes which spread the disease by 2020, even gross elephantiasis is seldom
the disease are active at night, facilitating the spread seen even in the developing countries of the world.
of the disease because the larvae are usually only found
in the blood between about 10 pm and 2 am.
IDENTIFICATION OF MAJOR
Treatment and Prevention MICROFILARIAL ORGANISMS
Several different medications and methods are used to The three major species of causative organisms of filariasis
treat a filariasis infection: eliminating the larvae by im- listed earlier in humans occupy certain niches, which lead
pairing the adult worms’ ability to reproduce, and by to their discovery and initial attempts at identification.
actually killing adult worms. Unfortunately, much of the Table 4-1 shows the general division of the organisms
tissue damage that occurs in the condition of elephan- based on the issue types each of the species typically in-
tiasis may not be reversible. The medication is started vade. Organisms infect humans and other vertebrates
at low doses to prevent immune reactions caused by through the bites of mosquitoes, gnats, and flies, depend-
large numbers of dying parasites. Although effective, ing upon the location. Human filarial nematode worms
medications used in treatment can cause severe side ef- have a complicated life cycle, which primarily consists of
fects in as many as 70 percent of patients as a result of five stages. After the male and female worm mate, the fe-
either the drug itself or the massive death of parasites in male gives birth to live microfilariae by the thousands. The
the blood. Diethylcarbamazine is implicated in causing microfilariae are taken up by the vector insect (intermedi-
severe allergic reactions and the formation of pus-filled ate host) during a blood meal. In the intermediate host, the
sores (abscesses). These side effects can be controlled by microfilariae molt and develop into third-stage (infective)
using antihistamines and anti-inflammatory drugs such larvae. Upon taking another blood meal the vector insect
as steroidal preparations called corticosteroids. In rare injects the infectious larvae into the dermis layer of our
cases, treatment with diethylcarbamazine in someone skin. After approximately one year the larvae molt through
with very high levels of parasitic infection may lead to a two more stages, maturing into the adult worm.