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213Introduction to Microbiology
Epidemiological determinants:
Agent factors:
1. The immediate source of infection is the feces
containing the cysts.
2. Period of communicability: As long as the feces contain
cysts.
Host factors:
1. Age and sex: It occurs in people of all ages of both sexes.
2. Immunity: The disease does not confer life-long
immunity.
Environmental factors:
1. Amoebiasis does not show a seasonal trend and
infection rates are higher during the rainy season.
2. Contaminated water and food increase the trans-
mission of disease.
Mode of transmission: The infection can spread when
infected people do not dispose of their feces in a sanitary
manner or do not wash their hands properly after going to the
toilet. Contaminated hands can then spread the parasites to
food that may be eaten by other people and surfaces that may
be touched by other people. Hands can also get contaminated
when changing the nappies of an infected infant. Amoebiasis
can also be spread by:
1. Drinking water contaminated with stools.
2. Eating contaminated raw vegetables and fruit.
3. Unprotected oral-anal sexual contact.
4. Poor sanitation and inadequate hygiene.
5. Through fertilizer made of human waste.
Clinical features:
1. Diarrhoea (which may contain blood).
2. Stomach cramps.
3. Fever.
4. Nausea.
5. Weight loss.
6. Stomach tenderness.
214 Social Pharmacy
Prevention and control:
1. Wash hands thoroughly with soap and water after
using the toilet.
2. Wash hands thoroughly with soap and water before
touching food.
3. Frequently clean bathrooms and toilets.
4. Wash raw vegetables before cooking.
5. Avoid eating uncooked foods while traveling.
Treatment: Metronidazole and tinidazole are used to treat
amoebiasis.
e. Food Poisoning
Food poisoning is an acute gastro-enteritis acquired through
ingestion of contaminated and injurious food or drinks.
Poisoning may occur due to living bacteria or their toxins or
inorganic chemical substances, and poisons derived from plants
and animals. It is characterized by a history of ingestion of
common food, attack of many persons at the same time, and
similarity of symptoms and signs in the majority of cases.
Causative agent: Bacterial food poisoning is caused by the
ingestion of foods contaminated by living bacteria or their
toxins.
Non-bacterial food poisoning is caused by chemicals such
as arsenic, tin, copper sulfate, fluorides, pesticides, fertilizers,
injurious preservatives, additives, and adulterants. The use of
cheap enamel-ware in which acidic foods dissolve antimony is
usually responsible for food poisoning.
1. Salmonellosis is caused by Salmonella typhimurium,
Salmonella enteritidis and Salmonella cholersuis. The
infection spreads through contaminated meat, milk and
milk products, sausages, custards, eggs, and egg
products. Infected rats and mice may also contaminate
foodstuffs with their feces and urine.
The incubation period: 10 to 24 hours.
The causative organism multiplies in the intestine
causing acute enteritis and colitis. The onset is sudden
with chills, fever, nausea, vomiting, and a profuse
watery diarrhea lasting for 2–3 days.
215Introduction to Microbiology
2. Staphylococcal food poisoning is caused by entero-
toxins of Staphylococcus aureus. Salads, custards, milk,
and milk products contaminated with Staphylococcus
are responsible for poisoning.
Incubation period: 1 to 6 hours. Poisoning occurs from
the ingestion of toxins by bacteria in the contaminated
food. The toxins act directly on the intestine and CNS.
Fever is rare.
3. Botulism is caused by exotoxin of Clostridium botulinum
usually found in under-processed foods. The organism
is widely distributed in soil, dust, and the intestinal
tract of animals. It enters the food as spores. Home-
preserved foods, smoked or pickled fish, homemade
cheese, and similar low-acid foods are chief sources of
botulism.
Incubation period:12 to 36 hours.
Botulism is characterized by dyspepsia, diplopia, ptosis,
dysarthria, blurring of vision, muscle weakness, etc. Fever is
generally absent. The toxin being thermolabile, food can be
rendered safe by heating at 100ºC for a few minutes before
use. Antitoxin acts as a prophylactic against botulism. Active
immunization with botulism toxoid is a preventive measure.
Guanidine HCl, 15 to 40 mg/kg body weight can be given
orally. Clostridium welchi, an anaerobic organism also causes
mild symptoms.
Prevention and control: Prevention of bacterial and chemical
contamination of foods is most important. This can be achieved
through hygienic food handling and the use of clean utensils.
Refrigeration of raw and processed food is also useful. Foods
should be prepared at adequate temperatures in clean utensils.
It should be kept covered to avoid access to rats, mice, flies,
and dust. Contaminated meat is a source of infection, the food
animals must be free from infection. The examination of animals
before and after slaughter by veterinary staff is yet another
preventive measure. Strict supervision of restaurants, canteens,
messes, etc. in respect of food quality and hygienic cooking
methods must be practiced. Over and above these measures,
216 Social Pharmacy
health education particularly for food handlers and their
hygiene is necessary for effective control of food poisoning.
f. Hookworm Infestation
A hookworm is a nematode, which lives in the small intestine
as a parasite. The eggs are excreted in the stools and develop
into larvae in warm moist soil. Whenever in contact with
human skin they penetrate it and are carried to the lungs, go
up the air passages and windpipe, and are finally swallowed.
Further development takes place in the small intestine. Two
species of hookworms, i.e. Ancylostoma duodenale and Necator
americanus commonly infect humans. The infection of A.
duodenale is common in Europe, Egypt, and India (Assam,
West Bengal, Bihar, Odisha, Andhra Pradesh, Tamil Nadu,
Karnataka, Kerala, and Maharashtra) whereas N. americanus
predominates in America, Sub-Saharan Africa, Southeast Asia,
Indonesia and China. Hookworms are thought to infect more
than 600 million people in the world including 45 million
Indians. Hookworm infestation causes severe anemia, joint
pain, dyspepsia, edema, and eosinophilia. This results in
lowered body resistance, retarded development in children,
mental retardation, and loss of efficiency in infested persons.
Causative agent: Ancyclostoma duodenale.
Incubation period: Eggs appear in the stools about 6 weeks
after penetration of the skin by larvae.
Mode of transmission: The infection is acquired through the
skin. When a person walks about barefoot in soil contaminated
with the stools of a hookworm patient, the infective larvae
penetrate through the skin of the feet.
Prevention and control: The affected persons must be treated
with Alcopar (bephenium hydroxy naphthoate) and Tetra-
chloroethylene. Proper disposal of excreta by the construction
and use of sanitary latrines is essential to prevent the pollution
of soil due to eggs excreted in the stools of the patients. Health
education of the people emphasizing the importance of wearing
shoes and not walking barefoot is recommended as a personal
217Introduction to Microbiology
preventive measure. Fresh stool should not be used as manure
rather it should be composted.
Treatment:
1. Benzimidazoles (albendazole and mebendazole) are the
most common treatment for hookworm infestation.
2. In certain circumstances, levamisole and pyrantel
pamoate may be used.
3. WHO also recommends anthelmintic treatment in
pregnant women after the first trimester. It is
recommended that if the patient also suffers from
anemia then Ferrous sulfate (200 mg) be administered
t.i.d at the same time as anthelmintic treatment; this
should be continued until hemoglobin values return to
normal, which could take up to 3 months.
C. Arthropod Borne Infections
a. Dengue
Dengue is a mosquito-borne viral disease. The infection causes
dengue fever (DF), which is a severe flu-like illness, and
sometimes develops into a potentially lethal complication called
dengue hemorrhagic fever (DHF).
Causative agent: Dengue is caused by a dengue Flavivirus
that has four distinct serotypes (DEN-1, DEN-2, DEN-3, and
DEN-4), belonging to the family Flaviviridae.
Incubation period: 3–14 days (usually 4–7 days).
Epidemiology: The disease, also called ‘break-bone’ fever
affects infants, children, and adults alike and could be fatal.
The global incidence of dengue has increased dramatically in
recent decades. An estimated 50–100 million dengue infections
occur annually mainly in urban and semi-urban areas in
tropical and subtropical countries.
The countries of South-East Asia region are divided into
3 categories:
a. Hyperendemic: India, Bangladesh.
b. Uncertain endemicity: Bhutan, Nepal
c. Non-endemic: Democratic Peoples Republic (DPR) of
Korea.
218 Social Pharmacy
Local variations in risk are influenced by rainfall,
temperature, and unplanned rapid urbanization. People who
have had a dengue infection before are likely to develop severe
dengue. Infants and pregnant women are at increased risk for
developing severe dengue.
Epidemiological determinants:
Agent factor:
1. The dengue virus has four serotypes, which are
designated DENV-1, DENV-2, DENV-3, and DENV-4.
2. Infection with any one serotype confers life-long
immunity to that virus serotype only.
Vector:
1. Aedes aegypti and aedes Albopictus are the two most
important vectors of dengue.
2. Aedes aegypti is a pure anthropophilic, nervous feeder
(i.e. it bites more than one host to complete one blood
meal) and is a discordant species (i.e. it needs more
than one feed for the completion of the gonadotropic
cycle).
3. Aedes albopictus is an aggressive feeder and concordant
species, i.e. the species can complete its blood meal in
one go on one person and also does not require an extra
feed for the completion of the gonotrophic cycle.
Environmental factors: The Aedes species survive best between
16°C–30°C and a relative humidity of 60–80 percent.
Mode of transmission:
1. Through mosquito bites: Dengue viruses spread to
people through the bites of infected Aedes species
mosquitoes (Ae. aegypti or Ae. albopictus).
2. A pregnant woman already infected with dengue can
pass the virus to her fetus during pregnancy or around
the time of birth.
3. Dengue can also spread through blood transfusion,
organ transplant, or through a needle stick injury.
Clinical features: A person infected by the dengue virus
develops severe flu-like symptoms. The clinical features of
dengue fever (DF) are:
219Introduction to Microbiology
1. High fever (40°C/104°F).
2. Muscle and joint pain.
3. Headache.
4. Nausea/vomiting.
5. Rashes.
6. Swollen glands.
7. Hemorrhagic manifestations.
8. Shock.
9. Respiratory distress.
10. Internal bleeding.
11. Organ impairment in serious cases.
Prevention and control:
1. Removal of natural and artificial habitats that support
the breeding of the mosquitoes.
2. Proper disposal of solid waste.
3. Use of clean domestic water storage containers.
4. Use of window screens, long-sleeved clothes, repel-
lents, insecticide treated materials, coils, and vaporizers.
5. Use of creams, lotions, or sprays containing mosquito
repellents.
6. Careful clinical detection and management of dengue
patients.
Treatment: There is no specific treatment for dengue fever.
Patients should take rest and drink plenty of fluids such as
water or drinks with added electrolytes. Paracetamol can be
taken to bring down fever and reduce joint pains.
b. Malaria
Malaria is a protozoal infection. It is one of the most important
health problems in India.
Causative organism: It is caused by the malarial parasites
(Plasmodium) viz. Plasmodium vivax, P. falciparum, P. malariae,
and P. ovale.
Incubation period: 10 to 30 days.
Epidemiology: The entire population is deemed to be under
malarial risk. People of all ages and both sexes are affected by
220 Social Pharmacy
malaria. There is no natural immunity and practically all races
are susceptible except the Negroes who are immune.
Epidemiological determinants:
a) Agent factors:
1. Malaria in man is caused by four distinct species of the
malaria parasite—P. vivax, P. falciparum, P. malariae, and
P. ovale. In India, maximum cases of infections are due
to P. falciparum
2. Reservoir of infection: The main reservoirs of malarial
parasites are humans, apes, and monkeys.
3. Period of communicability: Humans remain infective
as long as mature, viable gametocytes exist in the
circulating blood in sufficient density to infect vector
mosquitoes.
Host factors:
1. Age: Malaria affects all ages. Newborn infants have
considerable resistance to infection with P. falciparum.
2. Sex: Males are more frequently exposed to the risk of
acquiring malaria than females.
3. Race: Individuals with sickle-cell trait have a milder
illness with falciparum infection. Persons whose red
blood cells are “Duffy negative” (a genetic trait) are
resistant to P. vivax infection.
4. Pregnancy: Pregnancy increases the risk of malaria in
women.
5. Housing: Poor ventilated and poorly lighted houses
provide ideal indoor resting places for mosquitoes.
Environmental factors: India’s geographic position and
climatic conditions had been, for a long, favorable to the
transmission of malaria.
1. Season: Malaria is a seasonal disease. The maximum
prevalence is from July to November.
2. Temperature: The optimum temperature for the
development of malaria parasites is 16 to 30°C.
3. Humidity: When relative humidity is between 60–75%,
mosquitoes are more active and feet more voraciously.
221Introduction to Microbiology
4. Altitude: Mosquitoes or not available at high altitudes
(greater than 2000 to 2500 meters).
Mode of transmission:
1. Malaria is mainly transmitted through the bite of
infected female Anopheles mosquitoes. Mosquitoes
become infected after feeding on a person harboring
malarial parasites in the blood. The sexual cycle of the
parasite takes place in the mosquito and the parasite
develops into the infective stages (sporozoites) within
2–3 weeks. The sporozoites are injected into the new
susceptible host when the mosquito feeds on him. After
circulating for a short time in the blood of the human
being, the parasites enter the liver and develop into
form, which can invade the red blood cells and develop
into gametes. This completes the asexual cycle of the
parasite. The mosquito feeding on the man sucks the
gametes and thus the cycle of transmission continues.
2. Sometimes malaria is also transmitted through
transfusion of blood containing malarial parasites.
3. Congenital malaria (infection of the newborn from an
infected mother) is relatively rare.
Clinical features: Malaria is characterized by:
1. Cold stage: There is the sudden onset of fever with the
sensation of extreme cold, lasting for 15 to 60 minutes.
The person is very weak with a weak pulse.
2. Hot stage: In this skin, the patient is very hot and the
fever shoots up to 104ºC. The patient has a burning hot
and intense headache and feels uncomfortable. This
stage lasts for 2–6 hours.
3. Sweating stage: In this stage profuse sweating and fall in
temperature take place. This stage lasts for 2 to 5 hours.
Complications of malaria:
1. Anemia.
2. Direct organ damage: Hepatomegaly, splenomegaly,
renal failure, meningitis, encephalopathy.
3. Febrile herpes.
222 Social Pharmacy
Prevention and control: WHO has recommended the
following anti-malarial measures:
1. Prevention of man/vector contact using mosquito
repellants, protective clothing, bed nets, and screening
of houses.
2. Destruction of adult mosquitoes through the use of
insecticidal sprays including aerosols.
3. Effective sanitation, water management, and filling of
small-scale drains
4. Chemoprophylaxis and chemotherapy against the
malaria parasite.
Treatment:
1. Chloroquine is often used as an anti-malarial medi-
cation, though chloroquine-resistant infections are
common in some parts of the world.
2. Chloroquine-resistant infections are treated by
following drugs:
a. the combination of quinidine or quinine + doxy-
cycline/tetracycline/clindamycin.
b. Atovaquone plus proguanil (Malarone).
c. Mefloquine or artesunate.
d. the combination of pyrimethamine + sulfadoxine
(Fansidar).
3. Administration of intravenous fluids and respiratory
support may be needed.
c. Filariasis
It is a major public health problem in India. Filariasis is not
fatal but it disables and deforms a person especially due to
swelling of the legs and the external genitalia, a condition called
elephantitis.
Causative organism: Filariasis is caused by two nematode
worms: Wuchereria bancrofti and Wuchereria malayi.
Incubation period: 6 months–1 year.
Epidemiology: Filariasis is endemic all over India except in
Jammu and Kashmir. It is a communicable disease transmitted
through mosquito bites. Filariasis mainly affects the lymphatic