Epidemiology of Communicable Diseases: Vector-borne Diseases (Leishmaniasis, Malaria, Onchocerciasis)

Leishmaniasis

Causative Organism

Leishmaniasis is caused by Leishmania parasites. Different species are associated with different diseases:

• L. donovani complex, L. infantum, L. chagasi: Visceral leishmaniasis (Kala Azar)
• L. tropica, L. major, L. aethiopica, L. infantum: Cutaneous leishmaniasis
• L. mexicana complexes, L. braziliensis complex, L. amazonensis: Muco-cutaneous leishmaniasis

Endemicity

The distribution of cutaneous and visceral leishmaniasis worldwide is shown in maps from 2016, highlighting the number of new cases reported in various countries.

Transmission

Leishmaniasis is transmitted through the bite of phlebotomine sandflies. The transmission cycle involves:

1. Sandflies taking a blood meal from infected humans or animals.
2. The protozoan Leishmania parasite being transmitted to humans.

Vectors

• Sandflies are the primary vector for Leishmania parasites.

Reservoirs

• Humans
• Wild rodents
• Domestic dogs

Transmission Details

1. Natural transmission occurs from man to man via the bite of infected female sandflies.
2. Vertical transmission (mother to fetus), blood transfusion, and accidental lab inoculation are other transmission routes.
3. In zoonotic areas, transmission occurs from animal reservoirs through the bite of infective female sandflies.

Incubation Period

• Visceral leishmaniasis: Generally 2–6 months, but can range from 10 days to years.
• Cutaneous leishmaniasis: At least a week, up to many months.

Clinical Disease: Visceral Leishmaniasis

Symptoms

• Enlargement of the spleen and liver
• Night sweats
• Severe or irregular fever lasting weeks
• Bleeding
• Blackening of the skin
• Scaly, dark, or ashen skin
• Cough
• Weakness
• Substantial weight loss
• Thinning of hair
• Anemia

Clinical Disease: Cutaneous Leishmaniasis

Symptoms

• Breathing difficulty
• Skin sores that may become slow-healing ulcers
• Stuffy, runny nose and nosebleeds
• Swallowing difficulty
• Ulcers and erosion in the mouth, tongue, gums, lips, nose, and inner nose

Clinical Disease: Mucocutaneous Leishmaniasis

Symptoms

• Affects skin and mucous membranes, mainly of the mouth, throat, and nose
• Skin lesions (due to Cutaneous Leishmaniasis)
• Stuffy nose and breathing difficulties
• Nosebleeds
• Formation of multiple ulcers that spread across the mouth and nose, leading to disfigurement

Diagnosis

1. Microscopic identification of the nonmotile, intracellular amastigote form in stained specimens.
2. Culture using NNN (Novy-MacNeal-Nicolle) medium.
3. Serological testing:
   • Direct agglutination test (DAT)
   • Complement fixation test (CFT)
   • Indirect immunofluorescence (IIF)
   • Enzyme-linked immunosorbent assay (ELISA)

Treatment: Visceral Leishmaniasis

• Visceral disease always requires treatment.
• Medications like Pentastam (Sodium Stibogluconate Injection) are available.

Treatment: Cutaneous Leishmaniasis

• Cutaneous ulcers may heal without treatment.
• Treatment can:
  • Speed healing
  • Reduce scarring
  • Decrease risk of further disease
• Plastic surgery may be required for disfigurement.

Treatment: Mucocutaneous Leishmaniasis

• These lesions do not heal naturally and always require treatment.

Prevention

• Currently, no vaccine is available.

1. Health Education: Making the public aware of how the disease is caused and controlled.
2. Vector control:
   • Reducing the sandfly population by insecticidal spraying.
   • Environmental management.
   • Measures for reducing man-fly contact, such as mesh doors and repellents.
3. Control of parasite:
   • Diagnosis of infected individuals.
   • Administering complete treatment.
   • Controlling the reservoir.

Control Measures

• Control of cases:
  • Diagnosis
  • Notification
  • Treatment
• Control of contacts: Investigation of contacts, source of infection, local transmission cycle.

Malaria

Causative Organism

Malaria is caused by Plasmodium parasites. Different species cause different types of malaria:

• Plasmodium vivax: Causes tertian malaria
• Plasmodium malariae: Causes quartan malaria
• Plasmodium falciparum: Causes malignant malaria
• Plasmodium ovale: Causes ovale malaria

Global Status

The slides show countries with indigenous cases in 2000 and their status by 2017. Countries with zero indigenous cases for at least three consecutive years are considered malaria-free.

Transmission

Malaria is primarily vector-borne but can also be transmitted through other means:

• Vector-borne: via mosquitoes
• In utero transmission

Transmission Cycle

1. Initial human host gets infected.
2. Plasmodium sporozoites infect the liver.
3. The parasite infects the blood.
4. The next human host gets infected via a vector.

Vector

• Mosquitoes (specifically, female Anopheles mosquitoes)

Transmission Details

1. Bite of an infective female Anopheles mosquito.
2. Injection or transfusion of infected blood, or use of contaminated needles and syringes.
3. Congenital transmission occurs rarely.

Incubation Period

• Depending on parasite species, it ranges between 9 to 40 days.

Reservoir

• Humans are the primary reservoir, except for P. malariae, which is common to humans, African apes, and some South American monkeys.

Clinical Features

• Fever
• Chills
• Sweats
• Anorexia
• Nausea
• Lassitude
• Headache
• Muscle and joint pain
• Cough
• Diarrhea
• Anemia and/or splenomegaly often develop after some days.
• If untreated, the disease may progress to severe malaria.

Complications: Benign Malaria

• Anemia
• Splenomegaly
• Hepatomegaly
• Herpes labialis
• Renal complications

Complications: Malignant Malaria

• Cerebral malaria
• Acute renal failure
• Liver damage
• Dehydration
• Gastrointestinal symptoms
• Collapse
• Severe anemia
• Blackwater fever
• Hyperpyrexia
• Pulmonary oedema
• Hypoglycemia

Malaria in Pregnant Women

• Pregnant women are more vulnerable to falciparum malaria.
• Causes low birth-weight, anemia, severe complications, abortion, and premature delivery.

Diagnosis

1. Peripheral blood film of malaria:
   • Thin smear
   • Thick smear
2. Serological tests such as ICT.

Treatment

Uncomplicated falciparum malaria:

• First-line Treatment: Artesunate (AS) + Sulfadoxine Pyrimethamine (SP)

  Dosage based on age and weight

• In addition, a single dose of primaquine (0.25 mg base/kg bw, maximum dose 15 mg) should be added on the first day of treatment to ACT for uncomplicated falciparum malaria as a gametocytocidal medicine.

• Second-line Treatment: Artemether (20mg) + Lumefantrine (120mg)

Malaria caused by P. vivax, P. ovale and P. malariae:

• Chloroquine 25mg base / kg divided over three (3) days. (Chloroquine 4 tablets day 1, 4 tablets day 2, 2 tablets day 3) combined with Primaquine 0.25 mg/kg bw taken daily with food for 14 days for vivax and ovale

Severe Malaria

• First option: Artesunate I.V/I.M
• Second option: Artemether I.M
• Third option: Quinine I.V

Malaria in Pregnancy

• Malaria in pregnancy should be considered severe and treated in hospital
• Uncomplicated malaria in 1st trimester: Quinine + Clindamycine
• Uncomplicated malaria in 2nd & 3rd trimester: First option: (AS + SP), Second option: Quinine + Clindamycine
• Severe malaria: Artesunate Or Quinine + Clindamycine

Prevention

1. Vector control by:
   • Using long-lasting insecticidal nets (LLINs).
   • Indoor residual spraying with insecticides (IRS).
   • Control of larval stages by elimination of mosquito breeding sites.
2. Intermittent preventive treatment for pregnant women and infants and seasonal chemoprophylaxis for children 1-5 years of age.

Control Measures

• Control of cases: Diagnosis, Notification, Treatment
• Vector control: Physical, Biological, Chemical
• Susceptible people:
  • Personal protection (bed net, repellent .. etc)
  • Chemoprophylaxis
  • Health education

Onchocerciasis (River Blindness)

Causative Organism

• Onchocerca volvulus (also called as Filaria volvulus, Onchocerca caecutiens) - a filarial worm belonging to the class Nematoda

Distribution

The slide shows the distribution of onchocerciasis and the status of preventive chemotherapy (PC) in endemic countries in 2017.

Transmission

• Only through the bite of infected female blackflies of the genus Simulium

Transmission Cycle

1. Blackflies ingest microfilariae in the skin.
2. Microfilariae penetrate the stomach wall.
3. They migrate to the head and proboscis.
4. O. volvulus enters the skin through the fly bite.
5. They migrate to subcutaneous tissue.
6. They mate and produce microfilariae.

Reservoir

• Humans
• Chimpanzees and Gorillas. Onchocerca species found in animals cannot infect humans but may occur together with O. volvulus in the insect vector.

Clinical Features

• The adult worms are relatively non-pathogenic, and microfilarae are the main cause of the disease.
• In heavily infected individuals, the microfilarae are found in the skin, eyes, lymph nodes, and various internal organs of the body.
• Itching and scratching with secondary infection
• Severe dermatitis known as Sowda
• Hanging groin due to loss of elastic fibres in the skin
• Subcutaneous nodules known as onchocercomata
• Death of adult worm in lesion may lead to formation of abscess.
• Atrophy of skin giving premature aged appearance
• Dwarfism (shortness)
• Optic atrophy and blindness

Diagnosis

• Finding of adult worms:
  • Adult worms can be detected in the biopsy material of subcutaneous nodules.
• Finding of microfilaria:
  • Examination of skin snip from the area of maximum microfilarial density
  • Microfillaria can also be found in urine, sputum, blood, CSF, or lymph.

Prevention

1. Avoid bites of Simulium flies by:
   • wearing protective clothing
   • use of an insect repellent
2. Vectors control
3. Provide facilities for diagnosis and treatment.

Control Measures

1. Cases reported
2. Investigation of contacts and source of infection
3. Specific treatment: Ivermectin