(a) What do you mean by infectious and communicable diseases? Mention the causative agent and means of spread of filaria. Also…

Infectious and Communicable Diseases: Lymphatic Filariasis

An infectious disease is caused by the invasion and multiplication of pathogenic biological agents (bacteria, viruses, fungi, protozoa, or helminths) within a host tissue, regardless of transmission mode (e.g., tetanus). A communicable disease is a sub-class of infectious disease capable of being directly or indirectly transmitted from an infected host or reservoir to a susceptible individual (e.g., filariasis, tuberculosis).

Lymphatic filariasis is caused by thread-like tissue nematodes, predominantly Wuchereria bancrofti (responsible for 90% of global cases), Brugia malayi, and Brugia timori. The parasite is transmitted through the bite of infected female mosquito vectors, chiefly Culex quinquefasciatus in urban/semi-urban regions, Anopheles species in rural zones, and Mansonia species for Brugia. The infective third-stage larvae (L3) enter the human body via the bite puncture and migrate to the lymphatic system, maturing into adult worms.

Clinical manifestation occurs across three stages:

1. Asymptomatic microfilaraemia, where individuals harbor microfilariae without outward symptoms but exhibit subclinical lymphatic and renal damage.
2. Acute manifestations, including filarial fever, acute adenolymphangitis (ADL), and dermatolymphangioadenitis.
3. Chronic pathology, marked by irreversible lymphoedema, hydrocele, chyluria, and severe elephantiasis of limbs or genitalia due to lymphatic obstruction and secondary bacterial infections.

Diagnosis relies on peripheral blood examination by thick blood smear collected at night (10 PM–2 AM) to match nocturnal microfilarial periodicity; Immunochromatographic Card Tests (ICT) and Filariasis Test Strips (FTS) for circulating filarial antigen (CFA); and high-frequency ultrasonography (USG) to visualize live adult worms ("filarial dance sign") in scrotal or breast lymphatics.

Treatment and control utilize anti-helminthics: Diethylcarbamazine (DEC), Albendazole, and Ivermectin (triple-drug therapy, IDA). Preventive measures operate under the National Vector Borne Disease Control Programme (NVBDCP) through Mass Drug Administration (MDA), vector management via indoor residual spraying, integrated drainage sanitation, and adopting a One Health surveillance framework.

Carbon Cycle and Biotic-Abiotic Fluxes

The global carbon cycle operates through interconnected geological, oceanic, atmospheric, and terrestrial pools. Atmospheric carbon dioxide (~870 GtC) is fixed into organic matter via terrestrial and marine photosynthesis (~120 GtC/year terrestrially; ~50 GtC/year marine). Autotrophic and heterotrophic respiration, alongside microbial decomposition of detritus, return CO2 to the atmosphere.

`` [ Atmospheric CO2 Pool (~870 GtC) ] ^ | ^ ^ Respiration | | Photosyn. | Respiration & Combustion | v | | +-------------+-- [Terrestrial]---+ | Marine | [Biomass & Soil] | Biol. Pump | | v [Fossil Fuels] <--------+ [Oceanic Reservoir] (Combustion) (Dissolved CO2, HCO3-, Sedimentary Carbonates) ``

In oceans (~38,000 GtC pool), carbon is regulated by physical solubility and the "biological pump," where phytoplankton sequester carbon that eventually precipitates as carbonate sediments on the seafloor. Anthropogenic perturbations—primarily fossil fuel combustion and land-use changes—release ~10 GtC/year, exceeding natural sink capacities, emphasizing biological carbon sequestration as an imperative for climate mitigation policy.

Sexual Conflict and Selfishness in Animal Behaviour

Sexual conflict arises from evolutionary disagreements between sexes over reproductive investments, optimal mating rates, and parental care. It operates at two levels: intralocus conflict, where the same genetic locus under sexually antagonistic selection pulls traits away from sex-specific optima, and interlocus conflict, involving interactions between different loci expressed in males and females.

Selfish genetic elements exacerbate conflict through segregation distorters and meiotic drive systems (such as the *t*-haplotype in mice or SD locus in Drosophila), which bias transmission in their favour despite imposing host fitness costs.

Interlocus conflict drives chase-away sexual selection and morphological arms races:

1. Drosophila melanogaster: Male seminal fluid contains accessory gland proteins (Acps, e.g., sex peptide) that enhance male sperm competitiveness and stimulate female egg laying, but reduce female longevity and remating propensity.
2. Gerris (water striders): Males possess grasping abdominal claspers for coercive mating, against which females evolve anti-grasping spines and abdominal modifications to resist energetically costly surplus matings.
3. Cimex lectularius (bedbugs): Males bypass the reproductive tract via traumatic insemination through the female abdominal wall; females evolve the spermalege to minimize physiological damage and immune pathogen risk.
4. Stalk-eyed flies (Cyrtodiopsis): Male eye-span acts as an indicator of resistance to selfish X-linked meiotic drive genes, driving female preference.

Females resolve male coercive strategies via cryptic female choice and post-copulatory physiological filtering. Understanding sexual conflict is critical in evolutionary biology and conservation breeding, where captive pair-bonding mismatches can trigger severe reproductive depression.